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SUCCESSIONAL DEVELOPMENT OF FORESTED WETLANDS ON RECLAIMED
PHOSPHATE MINED LANDS IN FLORIDA
FINAL REPORT
VOLUME II
Mark T. Brown, Principal Investigator
and
Susan M. Carstenn, Project Manager
with
John Baker, B.J. Bukata, Tim Gysan, Kristina Jackson,
Kelly Chinners Reiss, and Melini Sloan,
Graduate Research Assistants
UNIVERSITY OF FLORIDA CENTER FOR WETLANDS
Department of Environmental Engineering Sciences
Gainesville, Florida 32611
Prepared for
FLORIDA INSTITUTE OF PHOSPHATE RESEARCH
1855 West Main Street
Bartow, Florida 33830 USA
Contact Manager: Steven G. Richardson
FIPR Project Numbers: 95-03-117R and 98-03-131
August 2002
DISCLAIMER
The contents of this report are reproduced herein as received from the contractor. The
report may have been edited as to format in conformance with the FIPR Style Manual.
The opinions, findings and conclusions expressed herein are not necessarily those of the
Florida Institute of Phosphate Research, nor does mention of company names or products
constitute endorsement by the Florida Institute of Phosphate Research.
PERSPECTIVE
The FIPR research program has considered several issues related to wetland
reconstruction on phosphate mined lands, including:
How should we rebuild and manage wetlands, and what can Nature do on its own?
How can we tell when wetlands are successfully restored?
To what extent do we need to manage nuisance species, such as primrose willow,
cattail and vines?
This research examined several factors that affect the development of forested
wetlands on reclaimed phosphate mined lands. Part of the research was based on the
premise that certain plants, e.g. primrose willow (Ludwigia peruviana) and cattail (Typha
spp.), that have been designated as "nuisance" species by the Florida Department of
Environmental Protection are really just early successional species that will be displaced by
trees as the forest canopy develops. The project examined the effects of shade (shade cloth
on frames to simulate a forest canopy) on primrose willow and cattail in the field, plus
greenhouse work on the effects of nutrients and shade on competition of these species with
sapling trees. Simultaneously, FIPR also conducted field experiments examining the effects
of actual forest canopy on primrose willow (see Richardson and Kluson 1999, listed below).
UF also studied the impact of vines on forested wetland development and looked at the
importance of microtopographic relief (e.g. small mounds and depressions) on tree growth
and understory species diversity in wetlands. The research also further documents the trends
in development of various indicators of wetland functions in reclaimed forested wetland
sites of various ages.
The reader is referred to the following related reports and papers:
Brown, M.T. and R.E. Tighe (eds.). 1991. Techniques and guidelines for reclamation of
phosphate mined lands. FIPR Publication No. 03-044-095.
Crisman, T.L., W.J. Streever, J.H. Kiefer and D.L. Evans. 1997. An evaluation of plant
community structure, fish and benthic meio- and macrofauna as success criteria for
reclaimed wetlands. FIPR Publication No. 03-086-135.
Erwin, K.L., S.J. Doherty, M.T. Brown and G.R. Best. 1997. Evaluation of constructed
wetlands on phosphate mined lands in Florida. FIPR Publication No. 03-103-139, Vols.
I, II, I .
Richardson, S.G. and R.A. Kluson. 1999. Managing nuisance plant species in forested
wetlands on reclaimed phosphate mined-lands in Florida. Proceedings of the 26th Annual
Conference on Ecosystem Restoration and Creation, p. 104-118. Tampa, Florida, May
1999.
Steven G. Richardson
FIPR Reclamation Research Director
ABSTRACT
Studies of wetlands developing on phosphate mined lands and under controlled
greenhouse conditions were conducted to evaluate the role of early successional species
in ecosystem development. Persistence under reduced light, nutrient cycling, and nutrient
sequestration were studied, as well as their role in developing and altering the physical
environment (microtopography). Finally, measurable wetland attributes showing
directional change with time were identified, and models of successional trajectories were
established from attribute data.
These studies suggested that early successional species may facilitate ecosystem
development and are not persistent within the developed wetland ecosystem. After three
years under low light levels mimicking canopy closure (30% of available sunlight),
primrose willow and cattails decreased in abundance and vigor. Cattail (Typha spp.) and
primrose willow (Ludwigia peruviana) contributed greater nutrient sequestration than
other common herbaceous species. Constructed wetlands dominated by primrose willow
and by Carolina willow (Salix caroliniana) had higher microtopographic relief than
systems where these species were not present. Native vines showed similar successional
trends and may contribute rather than detract from ecosystem development.
Several wetland attributes exhibited sufficient directional change with time so that
their trajectories show promise as a means of evaluating success. These include
trajectories for tree height, dbh, canopy cover, soil organic matter content, and bulk
density.
TABLE OF CONTENTS
VOLUME 2
CHAPTER 5 CHARACTERISTICS OF CONSTRUCTED HUMMOCKS IN
CREATED WETLANDS by E.T. Gysan, S.M. Carstenn, and
J. Baker .................................................................................................... 5-1
INTRODUCTION ............................................................................................... 5-1
Historical Perspective .............................................................................. 5-1
Site Inform ation ....................................................................................... 5-2
Purpose..................................................................................................... 5-6
M ETHODOLOGY .............................................................................................. 5-9
Humm ock Elevation M easurem ent.......................................................... 5-9
Establishm ent of Benchm arks...................................................... 5-9
Elevation M easurem ents............................................................ 5-9
Change in Area ........................................................................ 5-11
Water Level Measurement...................................... 5-11
Soil M oisture M easurem ent................................................................. 5-12
Tree M easurem ent ................................................................................ 5-12
Vegetation M easurem ent ..................................................................... 5-13
Photographic Record............... ................................................................ 5-14
RESULTS .......................................................................................................... 5-15
Humm ock-to-Hum m ock Comparison ................................................... 5-15
Change in Cross-Sectional Area .............................................. 5-15
Species Diversity ..................................................................... 5-15
Tree Growth ............................................................................. 5-20
Volum etric W ater Content....................................................... 5-23
Hummock-to-Off-Hummock Comparison........................................... 5-23
Species Diversity ..................................................................... 5-23
Tree Growth ............................................................................... 5-40
DISCU SSION .................................................................................................... 5-43
General ................................................................................................... 5-43
Agrifos ............................................................................................ 5-43
Cargill ........................................................................................ 5-47
TABLE OF CONTENTS (CONT.)
VOLUME 2
Chapter 5 (Cont.)
W etland Comparison ............................................................................. 5-48
Value of Hummocks in Wetlands.......................................................... 5-50
CON CLU SION S.......................................................................................... 5-53
R EFER EN CES ........................................................................................... 5-55
APPENDIX
5-A ELEVATION ALONG MAJOR AND MINOR
TRAN SECTS ...................................................................... 5A-1
5-B VOLUMETRIC WATER CONTENT AT ILUKA
RESOURCES WETLAND............................................5B-1
CHAPTER 6 THE ROLE OF VINES IN THE SUCCESSIONAL DEVELOPMENT
OF RECLAIMED FORESTED WETLANDS by K. Reiss .............. 6-1
IN TR O D U C TIO N ............................................................................................... 6-1
Statem ent of Problem ............................................................................... 6-1
Review of the Literature ................................... ............................... 6-2
V ines and Lianas ........................................................................ 6-2
Beneficial and Detrimental Roles of Vines ................... 6-2
Successional Trends of Vines .................................... 6-4
Edaphic Conditions Favoring Vine Growth .................. 6-5
Common Vines Occurring in Florida ............................ 6-5
Ecosystem Succession ............................................................... 6-7
W wetlands in Florida.............................................................. .. 6-10
Systems Modeling................................... 6-11
Plan of Study .......................................................................................... 6-12
M ETH O D S ............................................................................. .. 6-15
Description of Study Sites ..................................... ......... .. 6-15
Chronosequence Sampling Design ................................... ....... 6-19
TABLE OF CONTENTS (CONT.)
VOLUME 2
Chapter 6 (Cont.)
Site Selection ............................................................................. 6-19
Elongated Quadrat Establishment.............................................. 6-20
Vegetative Data Collection....................................................... 6-20
Vine Species Identification............................................ 6-20
Soil Characteristics ...................................................... 6-55
Intensive Sampling Design .................................................................. 6-69
Vegetative Data.......................................................................... 6-69
Abiotic Data ............................................................................. 6-76
Sunlight Transmittance ................................................ 6-76
W ater Depth................................................................. 6-76
Soil Characteristics ...................................................... 6-76
Simulation M odeling ............................................................... 6-83
DISCUSSION .................................................................................................... 6-99
Research Summary ................................................................................ 6-99
The Occurrence of Vines ................................................................... 6-100
The Roles of Vines in Succession....................................................... 6-103
Environmental Conditions Favorable to Vine Growth.................... 6-105
Limitations and Suggestions for Further Research............................ 6-107
Chronosequence Field Design ............................................... 6-107
Intensive Field Design ........................................................... 6-107
Further Research.................................................................... 6-107
CONCLUSIONS........................................................................................ 6-109
REFERENCES ................................................................................................ 6-111
APPENDIX
6-A LITERATURE REVIEW PERTAINING TO WETLAND
CONSTRUCTION .............................................................. 6A-1
6-B SYSTEM S ECOLOGY SYMBOLS......................................... 6B-1
TABLE OF CONTENTS (CONT.)
VOLUME 2
Chapter 6 (Cont.)
APPENDIX
6-C KRUSKAL-WALLIS TEST FOR VINES BASAL
DIAMETER ...................................................................6C-1
6-D MANN-WHITNEY TEST RESULTS FOR DBH OF
TREES NOT HOSTING AND HOSTING VINES............ 6D-1
6-E SOIL MOISTURE GRADIENTS ALONG WETLAND
TRAN SECTS ....................................................................... 6E-1
6-F ABOVE-GROUND VINE BIOMASS IN THE LAND-
SC A P E .................................................................................... 6F -1
CHAPTER 7 SELF-ORGANIZATION AND SUCCESSIONAL TRAJECTORIES
OF CONSTRUCTED FORESTED WETLANDS
by S.M C arstenn...................................................................................... 7-1
IN TR O D U CTIO N ............................................................................................... 7-1
Statem ent of Problem ............................................................................... 7-1
Review of Literature .............................................................................. 7-2
Successional Theory as a Basis for Ecosystem Construction
and Management................................................................... 7-2
Competing Views of Ecological Succession ............................. 7-5
Systems Perspective of Succession............................................ 7-7
W wetlands Succession............. ........................................................ 7-7
Soil Succession ............................................................................ 7-8
P lan of Study .......................................................................................... 7-10
M E TH O D S ........................................................................................................ 7-11
Site Selection and Description............................................................. 7-11
CF Industries SP1 ................................................................... 7-11
IMC-Agrico Clear Springs....................................................... 7-11
IMC-Agrico Parcel B............................................................... 7-11
Agrifos Consent Order 7984................................................... 7-15
M obil Sink Branch................................................................... 7-15
Cargill HP5 Phase 3 ................................................................. 7-15
IMC-Agrico FGGSB 2............................................................. 7-16
Cargill LP2 Phase 1 ................................................................. 7-16
C argill SP 6 ............................................................................... 7-16
1
TABLE OF CONTENTS (CONT.)
VOLUME 2
Chapter 7 (Cont.)
IM C-Agrico Cateye ................................................................. 7-16
Cargill SP11.......................................... .................................. 7-17
Guy Branch ......... .......... .......................................................... 7-17
IM C-Agrico M orrow Swam p .................................................... 7-17
Data Collection ...................................................................................... 7-17
Vegetation ................................................................................. 7-17
Canopy Photographs ................................................................ 7-20
Light Transm ittance............ .................................................... 7-22
Soil ............................................................................................. 7-22
Data Analysis ......................................................................................... 7-23
Vegetation ................................................................................. 7-23
Successional Trajectories of W wetlands ......................................7-25
RESULTS .......................................................................................................... 7-27
Chronosequence of W wetlands .............................................................. 7-27
Canopy Tree Species................................................................. 7-27
Subcanopy Tree Species .......................................................... 7-36
Shrub Species............................................................................. 7-36
Understory Species .................................................................. 7-39
Frequency of Occurrence of Species in the Understory ......... 7-48
Soil Developm ent...................................................................... 7-58
Successional Trajectories of Constructed Forested Wetlands ........... 7-72
Canopy Trajectories................................................................. 7-72
Subcanopy Trajectories.............................................................. 7-72
Shrub Trajectories.................................................................... 7-75
Understory Trajectories ........................................................... 7-75
Soil Trajectories ....................................................................... 7-75
DISCUSSION .................................................................................................... 7-81
Chronosequence of Constructed Forested Wetlands ........................... 7-81
xi
TABLE OF CONTENTS (CONT.)
VOLUME 2
Chapter 7 (Cont.)
Canopy Tree Species.................................................................. 7-81
Subcanopy Tree Species .......................................................... 7-86
Shrub Species............................................................................. 7-87
Understory Species .................................................................. 7-87
Soil Development...................................................................... 7-88
Successional Trajectories of Single Parameters .................................. 7-91
Canopy Trajectories................................................................. 7-96
Subcanopy Trajectories.............................................................. 7-97
Shrub Trajectories.................................................................... 7-97
Understory Trajectories ........................................................... 7-97
Soil Trajectories....................................................................... 7-97
Successional Trajectories of Emerging Properties .............................. 7-98
CONCLUSIONS........................................................................................ 7-113
REFERENCES ................................................................................................ 7-115
VOLUME 1
CHAPTER 1 EXECUTIVE SUMMARY by M.T. Brown & S.M. Carstenn............1-1
CHAPTER 2
CHAPTER 3
CHAPTER 4
EFFECTS OF SHADING ON NUISANCE SPECIES IN
CONSTRUCTED FORESTED WETLANDS ON PHOSPHATE-
M INED LAND by S.M Carstenn........................................................... 2-1
COMPETITION AND CONTRIBUTIONS OF PIONEER PLANTS
IN FORESTED WETLAND SUCCESSION AFTER PHOSPHATE
M INING by K.M Jackson...................................................................... 3-1
THE DEVELOPMENT AND ROLE OF MICROTOPOGRAPHY
IN NATURAL AND CONSTRUCTED FORESTED WETLANDS
by B.J. Bukata and M Sloan................................................................... 4-1
1
LIST OF FIGURES
VOLUME 2
Figure Page
Chapter 5
5.1 Constructed W etland Site Locations............................................................. 5-3
5.2 Agrifos Wetland As-Built Construction Plan with Location and Layout
of the Constructed Hummocks.................................................................. 5-4
5.3 Cargill Fertilizer, Inc. Phase 7 Wetland Map Showing Hummock
Location and Layout ................................................................................ 5-5
5.4 Iluka Resources Site 7 Wetland Map with Hummock Location and
Layout Show n ..................................................................................... 5-7
5.5 A Typical Hummock with Major and Minor Transects Shown as
Flagged Sampling Points. Major Transects Cover the Length of
the Hummock. Minor Transects Cover the Width of the Hummock..... 5-10
5.6 Changes in Cross-Sectional Areas for (a) Major and (b) Minor Transects
in the Agrifos Wetland. Standard Error Bars Are Calculated Using
the Excel 97 Chart W izard.................................................................... 5-16
5.7 Changes in Cross-Sectional Areas for (a) Major and (b) Minor Transects
in the Cargill Wetland. Standard Error Bars Are Calculated Using
the Excel 97 Chart W izard...................................................................... 5-17
5.8 Changes in Cross-Sectional Areas for (a) Major and (b) Minor Transects
in the Iluka Resources Wetland. Standard Error Bars Are Calculated
Using the Excel 97 Chart W izard ......................................................... 5-18
5.9 Percentage of Trees Surviving After One Growing Season in the Agrifos
Wetland. Six Trees of Each Species Were Originally Planted for
Each Hummock Soil Type .................................................................... 5-21
5.10 Changes in Tree Height and Basal Diameter for (a) Fraxinus caroliniana
and (b) Magnolia virginiana. Measured on the Hummocks at the
Beginning and End of the Growing Season in the Agrifos Wetland...... 5-22
5.11 Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on April 23, 1999, in the Agrifos Wetland. Water
Level Measured at 96.94 Ft. MSL ........................................................ 5-24
5.12 Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on May 19, 1999, in the Agrifos Wetland. Water
Level Measured at 97.28 Ft. MSL ........................................................ 5-25
5.13 Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on August 5, 1999, in the Agrifos Wetland. Water
Level M measured at 97.33 Ft. M SL ........................................................ 5-26
5.14 Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on October 13, 1999, in the Agrifos Wetland. Water
Level M measured at 97.42 Ft. M SL ........................................................ 5-27
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 5 (Cont.)
5.15 Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point During Summer 2000 in the Agrifos Wetland. Water
Level Measured at 97.52 and 98.15 Ft. MSL ....................................... 5-28
5.16 Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on September 13, 1999, in the Cargill Wetland.
Water Level Measured at 125.15 Ft. MSL ............................................. 5-29
5.17 Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on November 1, 1999, in the Cargill Wetland.
Water Level Measured at 125.88 Ft. MSL ............................................. 5-30
5.18 Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on June 2000 in the Cargill Wetland. Water Level
M measured at 125.62 Ft. M SL ................................................................ 5-31
5.19 Values for Average Volumetric Water Content Plotted with Minimum
and Maximum Values for Each Hummock in the Agrifos Wetland
on A pril 23, 1999 .................................................................................... 5-32
5.20 Values for Average Volumetric Water Content Plotted with Minimum
and Maximum Values for Each Hummock in the Agrifos Wetland
on M ay 19, 1999 ..................................................................................... 5-33
5.21 Values for Average Volumetric Water Content Plotted with Minimum
and Maximum Values for Each Hummock in the Agrifos Wetland
on A ugust 5, 1999................................................................................... 5-34
5.22 Values for Average Volumetric Water Content Plotted with Minimum
and Maximum Values for Each Hummock in the Agrifos Wetland
on October 13, 1999 .............................................................................. 5-35
5.23 Values for Average Volumetric Water Content Plotted with Minimum
and Maximum Values for Each Hummock in the Agrifos Wetland
in Sum m er 2000...................................................................................... 5-36
5.24 Values for Average Volumetric Water Content Plotted with Minimum
and Maximum Values for Each Hummock in the Cargill Wetland
on Septem ber 13, 1999 ......................................................................... 5-37
5.25 Values for Average Volumetric Water Content Plotted with Minimum
and Maximum Values for Each Hummock in the Cargill Wetland
on N ovem ber 1, 1999.............................................................................. 5-38
5.26 Values for Average Volumetric Water Content Plotted with Minimum
and Maximum Values for Each Hummock in the Cargill Wetland
on June 2, 2000 ....................................................................................... 5-39
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 6
6.1 Energy Systems Diagram Showing Characteristics of Reclaimed
Forested Wetlands, Highlighting Interactions Between Both
Herbaceous and Woody Vines and Other Components within
the W etland Systems Boundary............................................................ 6-13
6.2 Locator Map of the Central Florida Phosphate District. Each Study Site
Is Located According to Phosphate Mine Location (FIPR 1997)........... 6-16
6.3 Chronosequence Field Layout and Sampling Design. (a) Elongated
Quadrats Were Placed Perpendicular to the Hydrologic Gradient;
(b) A Square Meter Quadrat Was Placed Randomly Within Each
10 Meter Segment of the Elongated Quadrat. Each Elongated
Quadrat Was Extended Three Meters Wide on Each Side to Sample
Vine Cover on Trees ............................................................................. 6-21
6.4 The Volume Used Within the Square Meter Quadrats Begins at the
Forest Floor and Extends Beyond the Tree Canopy............................. 6-22
6.5 Energy Systems Diagram Showing Successional Changes in Herbaceous
Vine Biomass, Woody Vine Biomass, and Tree Biomass for
Constructed Forested W etlands........................................................... 6-30
6.6 Energy Systems Diagram Showing Each Coefficient Assigned in the
Model of the Role of Vines in Forested Wetland Succession ............... 6-34
6.7 Vine Distribution Over Time on the Chronosequence Sites. (a) Mean
Number of Rooted Vines; (b) Mean Dry Weight Vine Biomass; and
(c) Mean Vine Basal Diameter at Each Site ......................................... 6-39
6.8 Vine Presence on the Chronosequence Sites. (a) Vine Species Richness
Increases with Increasing Site Age; (b) Vines Representing 18
Genera Were Identified throughout the Nine Chronosequence Sites..... 6-41
6.9 Presence of Vines in Relation to Understory Herbaceous Cover on the
Chronosequence Sites. (a) Rooted Vines; (b) Vine Biomass .............. 6-45
6.10 Percent of Quadrats Containing Vine Increases in Relation to Increasing
Site Age Along the Chronosequence of Sites. It Is Possible that the
Total Frequency of Herbaceous Vines and Woody Vines Exceed 100%
Because Both Herbaceous and Woody Vines Could Be Recorded in
the Sam e Quadrat.................................................................................... 6-46
6.11 The Percent Cover of Vines on Trees. When a Tree Has Some Amount
of Vine Biomass Growing on It, (a) Shows the Affinity for Each
Host Tree Species To Be Covered in Vines, and (b) Shows the
Probability of Vine Cover for a Tree at a Given Age. Data Were
Not Available for Sink Branch ............................................................. 6-49
6.12 Mean DBH for Trees Hosting Vines and Trees Not Hosting Vines............ 6-52
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 6 (Cont.)
6.13 Vine Presence According to Sunlight Transmittance (%) on the
Chronosequence Sites. (a) Compares the Rooted Vines (#/m2) and
(b) the W eight of Vine Biomass (g/m2) ................................................ 6-53
6.14 Vine Distribution in the Landscape According to the Soil Moisture
Correlating with Tree Basal Area. (c) Shows the Correlation Between
Increased Basal Area and Decreased Sunlight Transmittance.............. 6-54
6.15 Vine Distribution in the Landscape According to the Soil Moisture
on the Chronosequence Sites. (a) Compares the Rooted Vines
(#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)....................... 6-58
6.16 The Number of Rooted Vines Relating to Soil Moisture on Gradients
Through the Wetland. Hydric Hammock is a Fringing Wetland.
(a) Shows the 40 Meter Long Transect 1; (b) Shows the 30 Meter
Long Transect 2; (c) Shows the 30 Meter Long Transect 3 ................. 6-59
6.17 The Number of Rooted Vines Relating to Soil Moisture on Gradients
Through the Wetland. Sink Branch Borders Two Stream Channels.
(a) Shows the 40 Meter Long Transect 1; (b) Shows the 40 Meter
Long Transect 2; (c) Shows the 60 Meter Long Transect 3 ................. 6-60
6.18 Vine Distribution in the Landscape According to the Dry Soil Bulk
Density on the Chronosequence Sites. (a) Compares the Rooted
Vines (#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)............... 6-61
6.19 Vine Distribution in the Landscape According to the Soil Organic
Matter Content on the Chronosequence Sites. (a) Compares the
Rooted Vines (#/m2) and (b) the Dry Weight of Vine Biomass (g/m2).. 6-63
6.20 Vine Distribution in the Landscape According to the Soil Calcium
Concentrations on the Chronosequence Sites. (a) Shows the Rooted
Vines (#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)....................... 6-65
6.21 Vine Distribution in the Landscape According to the Soil Magnesium
Concentrations on the Chronosequence Sites. (a) Shows the Rooted
Vines (#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)............... 6-66
6.22 Vine Distribution in the Landscape According to the Soil Potassium
Concentrations on the Chronosequence Sites. (a) Shows the Rooted
Vines (#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)............... 6-67
6.23 Vine Distribution in the Landscape According to the Soil Phosphorus
Concentrations on the Chronosequence Sites. (a) Shows the Rooted
Vines (#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)............. 6-68
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 6 (Cont.)
6.24 Vine Distribution in the Landscape According to the Soil Iron Concen-
trations on the Chronosequence Sites. (a) Shows the Rooted Vines
and (b) the Dry Weight of Vine Biomass ............................................... 6-70
6.25 Vine Distribution in the Landscape According to the Soil Ammonium
(NH4-N) Concentrations on the Chronosequence Sites. (a) Shows the
Rooted Vines (#/m2) and (b) the Dry Weight of Vine Biomass (g/m2) ..6-71
6.26 Vine Distribution in the Landscape According to the Soil Nitrate (NO3-N)
Concentrations on the Chronosequence Sites. (a) Shows the Rooted
Vines (#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)............... 6-72
6.27 Vine Distribution on the Intensive Sites. (a) Shows the Mean Number
of Rooted Vines; (b) Shows the Mean Dry Weight Vine Biomass;
(a) Shows the Mean Vine Basal Diameter at Each Site........................ 6-73
6.28 Vine Presence According to the Understory Herbaceous Cover on the
Intensive Sites. (a) Represents Quadrats with No Rooted Vines,
Rooted Herbaceous Vines, and Rooted Woody Vines; (b) Shows
Quadrats with No Harvested Vine Biomass, Herbaceous Vine
Biomass, and W oody Vine Biomass.................................................. 6-74
6.29 The Mean Vine Leaf Area (# of Leaves/m2) According to (a) Site Age
(Years) and (b) the Braun-Blanquet Cover Abundance on the
Intensive Sites. 1 (< 10% Cover), 2 (0-25% Cover), 3 (25-50%
Cover), 4 (50-75% Cover) and 5 (75-100% Cover) ............................. 6-75
6.30 Vine Presence According to Sunlight Transmittance (%) on the Intensive
Sites. (a) Compares the Rooted Vines (#/m2) and (b) the Dry Weight
of Vine Biom ass (g/m2) ....................................................................... 6-77
6.31 Vine Presence in Relation to Water Depth (cm) Within Each Square
Meter Quadrat. (a) Rooted Vines (#/m2) and (b) Vine Biomass (g/m2).
Only the Herbaceous Vine Mikania scandens (Climbing Hemp Vine)
Was Found Rooted in Standing Water.................................................. 6-78
6.32 Vines Occur in Various Ranges of Soil Moisture on the Intensive Sites.
(a) Shows the Mean Soil Moisture in Quadrats with No Rooted
Vines, Rooted Herbaceous Vines, and Rooted Woody Vines; (b)
Shows the Mean Soil Moisture in Quadrats Where No Vine
Biomass, Herbaceous Vine Biomass, and Woody Vine Biomass
W ere H arvested....................................................................................... 6-79
xvii
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 6 (Cont.)
6.33 Vines Occur in Various Ranges of Soil Bulk Density (g/cm3) on the
Intensive Sites. (a) Shows the Mean Bulk Density in Quadrats with
No Rooted Vines, Rooted Herbaceous Vines, and Rooted Woody
Vines; (a) Shows the Mean Bulk Density in Quadrats Where No
Vine Biomass, Herbaceous Vine Biomass, and Woody Vine Biomass
W ere H arvested................................................................................. 6-80
6.34 Vines Occur in Various Ranges of Soil Organic Matter (%) on the
Intensive Sites. (a) Shows the Mean Soil Moisture in Quadrats with
No Rooted Vines, Rooted Herbaceous Vines, and Rooted Woody
Vines; (b) Shows the Mean Soil Moisture in Quadrats Where No
Vine Biomass, Herbaceous Vine Biomass, and Woody Vine Biomass
W ere H arvested............................... ..................................................... 6-81
6.35 The Relationship Between Soil Moisture, Bulk Density, and Organic
M atter Content........................................................................................ 6-83
6.36 Vine Distribution in the Landscape According to the Soil Calcium
Concentrations on the Intensive Sites. (a) Shows the Rooted Vines
(#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)....................... 6-85
6.37 Vine Distribution in the Landscape According to the Soil Magnesium
Concentrations on the Intensive Sites. (a) Shows the Rooted Vines
(#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)........................ 6-86
6.38 Vine Distribution in the Landscape According to the Soil Potassium
Concentrations on the Intensive Sites. (a) Shows the Rooted Vines
(#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)....................... 6-87
6.39 Vine Distribution in the Landscape According to the Soil Phosphorus
Concentrations on the Intensive Sites. (a) Shows the Rooted Vines
(#/m2) and (b) the Dry Weight of Vine Biomass (g/m2)....................... 6-88
6.40 Vine Distribution in the Landscape According to the Soil Iron Concen-
trations on the Intensive Sites. (a) Shows the Rooted Vines (#/m2)
and (b) the Dry Weight of Vine Biomass (g/m2) .................................. 6-89
6.41 Vines Occur in Various Ranges of Soil Nitrogen (g NH4-N/m3) on the
Intensive Sites. (a) Shows the Mean Soil Moisture in Quadrats with
No Rooted Vines, Rooted Herbaceous Vines, and Rooted Woody
Vines; (b) Shows the Mean Soil Moisture in Quadrats Where No
Vine Biomass, Herbaceous Vine Biomass, and Woody Vine Biomass
W ere H arvested.............................................................. ........... 6-90
xviii
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 6 (Cont.)
6.42 Vines Occur in Various Ranges of Soil Nitrogen (g NO3-N/m3) on the
Intensive Sites. (a) Shows the Mean Soil Moisture in Quadrats with
No Rooted Vines, Rooted Herbaceous Vines, and Rooted Woody
Vines; (b) Shows the Mean Soil Moisture in Quadrats Where No
Vine Biomass, Herbaceous Vine Biomass, and Woody Vine Biomass
W ere H arvested....................................................................................... 6-91
6.43 Initial Start-Up Conditions for the Computer Simulation Model of the
Role of Vines in Succession ................................................................. 6-94
6.44 Simulation Showing Forested Wetland Succession in the Absence of
V ines ....................................................................................................... 6-94
6.45 In This Simulation, Vine Management in the Form of Herbicide and
Manual Removal of Vine Biomass Has Occurred in Year 7, Mimicking
Common Practices by Reclamation Companies................................... 6-95
6.46 Simulation with Vine Management in the Form of Herbicide and
Manual Removal of Vine Biomass Whenever the Storage of Herba-
ceous Vine Exceeds 20% of Storage .................................................... 6-97
Chapter 7
7.1 A Successional Trajectory. Dotted Line Represents the Actual Para-
meter of Interest Could It Be Known. The Solid Black Line
Represents the Parameter as Measured in the Field. The Area
Between the Two Gray Lines Represents an Acceptable Range of
Variation Around the Measured Parameter. Above and Below This
Area Represents a Region of Unrealistic Expectations and a Region
of Concern, Respectively ........................................................................ 7-4
7.2 Research Sites for the Investigation of Successional Trajectories of
Constructed Forested W wetlands ............................................................ 7-12
7.3 Wetland Transects of Varying Length (a) Were Established in Con-
structed Wetlands Beginning at the Wetland Edge and Extending
Downslope. Transects Were Divided into 10 Meter Segments (b)
Canopy and Subcanopy Trees Were Sampled Within 3 Meters of
Each Side of the Transect. Canopy Height Was Estimated at One
Random Point (H). A Nested 9 m2 Quadrat and a 1 m2 Quadrat
Were Randomly Located Within Each 10 m Segment (c) for Identifying
Shrubs and Herbaceous Vegetation, Respectively. Location of Canopy
Photos (P), Light Measurements (L) and Soil Samples (S) Are as
Indicated W within Each Quadrat.............................................................. 7-19
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 7 (Cont.)
7.4 Canopy Cover Analysis (a) Canopy Photograph and (b) High-Contrast
Black and White Image After Computer Enhancement. This is an
Example of 75% Cover ........................................................................... 7-21
7.5 Frequency Distribution of Tree Diameter at Breast Height from the
Chronosequence of Constructed Forested Wetlands. (Size Class Bins:
0-5 cm, 5.1-10 cm, 10.1-15 cm, 15.1-20 cm, 20.1-25 cm...) Sites
Appear in Chronological Order ..........................................7-31, 7-32, 7-33
7.6 Diameter at Breast Height Size Class Frequency Distributions by
Species .................................................................................... 7-34, 7-35
7.7 Understory Plant Community Status for the Chrono-Sequence of
Wetlands Graphed Against Age. Line Represents the Mean Under-
story Plant Community Status for All Sites............................................ 7-50
7.8 Number of Plant Species of Each Wetland Status Found in the Understory.
One Sampling Quadrat Was Randomly Located in Each 10-Meter
Transect Section: (a) FGGSB-2 Transect 1, (b) FGGSB-2 Transect 2,
(c) East Lobe Transect 1 and (d) East Lobe Transect 2............... 7-51, 7-52
7.9 The Frequency of Occurrence of Understory Species (< Im in Height)
Under Varying Light Transmittance Classes. Those Species
Occurring at a Minimum of Ten Sampling Points Throughout the
Chronosequence of Wetlands Are Presented. The X-Axis Is in
Reverse Order So That Species Occurring Under Low Light
Transmittance Levels Occur on the Right ................ 7-53, 7-54, 7-55, 7-56
7.10 On the Left, Available Nutrients on a Mass Basis (mg Nutrient g'1 Soil)
and an Areal Basis (g Nutrient m-2 to a Depth of 20 cm, on the Right).
Ca (a,b), Mg (c,d), K (e,f), P (g,h) and Fe (i,j) ...................7-60, 7-61, 7-62
7.11 Average KCI Extractable NO3-N, NH4-N and Combined NO3-N and
NH4-N at Each Site. In Graphs (a), (c), and (e) Nutrient Values Are
Expressed in Milligrams Nutrient Per Gram of Soil. In Graphs (b),
(d), and (f), Nutrient Values Are Expressed in Grams of Nutrient per
Square M eter to a Depth of 20 cm ..................................................... 7-63
7.12 Three Relationships Among Soil Parameters Are Graphed: (a) Soil
Water Content vs. Bulk Density, (b) Soil Organic Matter vs. Bulk
Density and (c) Soil Water Content vs. Organic Matter....................... 7-64
7.13 The Relationship Between Soil Water Content and Bulk Density in a
Chronosequence of Constructed Forested Wetlands. Sites Are
Presented in Chronological Order.......................................7-65, 7-66, 7-67
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 7 (Cont.)
7.14 The Relationship Between Soil Organic Matter and Bulk Density in a
Chronosequence of Constructed Forested Wetlands. Sites Are
Presented in Chronological Order................................................7-68, 7-69
7.15 The Relationship Between Soil Water Content and Organic Matter
in a Chronosequence of Constructed Forested Wetlands. Sites Are
Presented in Chronological Order.......................................7-70, 7-71, 7-72
7.16 Canopy Tree Trajectories in Constructed Forested Wetlands: (a) Power
Regression on Tree Height, (b) Power Regression on Tree Diameter,
and (c) Logarithmic Regression on Canopy Cover............................... 7-73
7.17 Subcanopy Tree Trajectories in a Chronosequence of Constructed
Forested Wetlands: (a) Species Richness Including Early and Late
Successional Species, (b) Subcanopy Species Stem Density, (c) Sub-
canopy Stem D iam eter............................................................................ 7-74
7.18 Shrub Trajectories in Constructed Forested Wetlands: (a) Shrub Species
Richness, (b) Shrub Stem Density, and (c) Stem Diameter.................. 7-76
7.19 Understory Trajectories in Constructed Forested Wetlands: (a) Herba-
ceous Species Richness, (b) Species Richness of All Herbaceous and
Woody Species, (c) Species Diversity, and (d) Cover Abundance......... 7-77
7.20 Understory Trajectories in Constructed Forested Wetlands (a) Canopy
Tree Species Richness, (b) Subcanopy Tree Species Richness,
(c) Shrub Species Richness, and (d) Vine Species Richness Plotted
A against Site A ge ..................................................................................... 7-78
7.21 Frequency of Occurrence of(a) Canopy Tree Seedlings, (b) Vines,
(c) Subcanopy Species, and (d) Shrub Species in the Understory of
Constructed Forested W wetlands ............................................................ 7-79
7.22 Average (a) Soil Organic Matter and (b) Bulk Density Plotted by
Site A ge................................................................................................... 7-80
7.23 Frequency of Occurrence of Canopy Tree Species in Florida's Wetland
Communities: (a) All Dominant Species (from Davis and others 1991)
and (b) Only Those Species Occurring in Both Natural and Constructed
Communities. See Table 17 for Species Code..................................... 7-83
7.24 Relative Frequency of Canopy Tree Species in Constructed Forested
Wetlands. The Graph Includes Only Those Species Found in Natural
and Constructed W wetlands .................................................................... 7-85
7.25 Frequency of Occurrence of(a) Canopy, (b) Subcanopy and (c) Shrub
Species in the Understory of Constructed Forested Wetlands.............. 7-89
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 7 (Cont.)
7.26 Frequency of Occurrence of Parthenocissus quinquefolia, Smilax sp.,
Toxicodendron radicans and Vitas rotundifolia in (a) Natural Com-
munities in Florida and (b) Constructed Forested Wetlands; and (c)
Frequency of Occurrence of Other Vines Species in Constructed
Forested W etlands................................................................................... 7-90
7.27 Available Soil Nutrient Signatures in Florida's Natural Communities:
(a) Xeric Pine, (b) Mesic Hardwood, (c) Flatwoods, (d) Lake Fringe,
(e) Marsh, (f) Bayhead, (g) Cypress Dome, and (h) Hardwood Swamp
(from Davis and others 1991) ...................................................... 7-92, 7-93
7.28 Available Soil Nutrient Signatures for Constructed Forested Wet-
lands......................................................................................7-94, 7-95, 7-96
7.29 The Successional Trajectories of Organic Matter and Bulk Density in
Those Sites That Were Identified as Better Than Average Wetlands
Using the Understory Community Wetland Status............................... 7-99
7.30 Hypothetical Community Basal Area Trajectories Based on (a) Exponential
Regression of Mean Community Basal Area of Research Sites and (b)
Exponential Curve Modified to a Logistic Growth Curve. Horizontal
Dotted Line Represents the Community Basal Area of a Natural Mixed
Hardwood Swamp........ ... ..................................................................... 7-100
7.31 Three Relationships Between Soil Parameters: (a) Soil Moisture vs. Bulk
Density, (b) Soil Organic Matter vs. Bulk Density and (c) Soil Water
Content vs. Soil Organic Matter. Data Used to Construct the Relation-
ships Were from Those Sites Falling Below the Average for Plant
Community Wetland Status in Figure 13. The Gray Line Represents
the Regression for All Subsamples. Those Samples Falling in the
Unshaded Region Above the Gray Line Have Exceeded the Mean for
That Relationship ................................................................................. 7-103
7.32 Ninety-Five Percent Confidence Intervals for Relationships Between
(a) Soil Water Content and Bulk Density, (b) Soil Organic Matter
and Bulk Density, and (c) Soil Water Content and Soil Organic Matter.
Gray Lines Represent the Upper and Lower Bounds of a 95%
Confidence Interval................................ ............................................ 7-105
7.33 Soil Relationships at LP2 Phase 1, a One-Half-Year Old Constructed
Forested Wetland. Gray Line Represents the Composite Value for
All Sites. Circles and Black Line Are from LP2 Phase 1 Only.......... 7-106
xxii
LIST OF FIGURES (CONT.)
VOLUME 2
Figure Page
Chapter 7 (Cont.)
7.34 Soil Relationships at CO7984, a Five-Year-Old Constructed Forested
Wetland. Gray Line Represents the Composite Value for All Sites.
Circles and Black Line Are from CO7984 Only ................................ 7-107
7.35 Soil Relationships at East Lobe, a Ten-Year-Old Constructed Forested
Wetland. Gray Line Represents the Composite Value for All Sites.
Circles and Black Line Are from East Lobe Only.............................. 7-108
7.36 Soil Relationships at Guy Branch, a Fifteen-Year-Old Constructed
Forested Wetland. Gray Line Represents the Composite Value for
All Sites. Circles and Black Line Are from Guy Branch Only............ 7-109
7.37 Soil Relationships at Parcel B, a Nineteen-Year-Old Constructed
Forested Wetland. Gray Line Represents the Composite Value for
All Sites. Circles and Black Line Are from Parcel B Only ............... 7-110
xxiii
LIST OF TABLES
VOLUME 2
Table Page
Chapter 5
5.1 Hummock Comparison Based on Species Diversity Indices for Agrifos,
Cargill, and Iluka W wetlands ............................................................... 5-19
5.2 Hummock and Off-Hummock Species Diversity Comparison for
Agrifos, Cargill, and Iluka W etlands.................................................... 5-41
5.3 Community Similarity Between Hummock and Off-Hummock Species.... 5-42
5.4 Average Values for Tree Parameters On and Off the Hummocks in the
Agrifos and Iluka W wetlands .................................................................. 5-43
Chapter 6
6.1 Site Descriptions of Research Sites, Including Company Ownership,
Mine Location, Year Planted, Age at Sampling, Area, Hydrology,
Soils, Mulched, Understory Plantings, and Nuisance Species
C control .................................................................................................... 6-17
6.2 Mathematical Equations Used in the Model of the Role of Vines in
Forested W etland Succession ...................................................... 6-32, 6-33
6.3 Steady-State Values Used in the Model of the Role of Vines in
Forested W etland Succession ............................................................... 6-35
6.4 Vine Species Found Growing on the Chronosequence Sites..................... 6-38
6.5 Frequency of Occurrence for the Vines Present in the Square Meter
Quadrats Sampled on the Chronosequence Sites.................................. 6-42
6.6 The Climbing Mechanisms of Vines Found on Reclaimed Forested
W wetlands ................................................................................................. 6-43
6.7 Summary Table for Tree Parameters on the Chronosequence Sites............ 6-47
6.8 Tree Genera Found Distributed Throughout the Chronosequence Sites..... 6-48
6.9 Percent of Trees Throughout the Landscape Hosting Vines. Dashed
Lines Signify that the Particular Tree Did Not Occur Within the
Particular Elongated Quadrat................................................................ 6-51
6.10 Summary Soil Data for the Chrono-Sequence Sites, Including Soil
Moisture (%), Dry Bulk Density (g/cm3), and Soil Organic Matter (%).
Values Represent the Mean Value 1 Standard Deviation.......... 6-56, 6-57
6.11 Summary of the Soil Nutrient Data for the Chrono-Sequence Sites.
Values in g/cm3 Represent the Mean Value 1 Standard Deviation..... 6-64
6.12 Summary Soil Data for Intensive Sites, Including Soil Moisture (%),
Dry Bulk Density (g/cm3), and Soil Organic Matter (%). Values
Represent the Mean Value 1 Standard Deviation................................ 6-79
xxV
LIST OF TABLES (CONT.)
VOLUME 2
Table Page
Chapter 6 (Cont.)
6.13 Summary of the Soil Nutrient Data for Intensive Sites. Values in g/m3
Represent the Mean Value 1 Standard Deviation................................ 6-84
Chapter 7
7.1 Individual Parameters and Emerging Properties Established for Vegetation
Structural Categories and Soils.............................................................. 7-3
7.2 Summary of Research Sites ...................................... 7-13, 7-14
7.3 Frequency of Occurrence of Canopy, Subcanopy and Shrub Species Found
in Constructed Forested Wetlands ........................................7-28, 7-29
7.4 Canopy Tree Data Collected from a Chronosequence of Constructed
Forested W etlands................ .................. 7-30
7.5 Subcanopy Tree Data Collected in a Chronosequence of Constructed
Forested W etlands....................... ............................... ...................... ....... 7-37
7.6 Shrub Data Collected from a Chronosequence of Constructed Forested
W wetlands ....................................... ...................................................7-38
7.7 Frequency of Occurrence (No. of Quadrats Present/Total No. of
Quadrats Sampled) of Canopy, Subcanopy, Shrub and Vine Species
(< 1 m in Height) Found in the Understory of Constructed
Forested W etlands............................................. ............................7-40, 7-41
7.8 Frequency of Occurrence of Herbaceous Species Found in the Understory
of Constructed Forested Wetlands.....................7-42, 7-43, 7-44, 7-45, 7-46
7.9 Understory Species Cover, Richness and Diversity of Vegetation Less
Than 1 Meter in Height................................. ........... 7-47
7.10 Probability of Sampling Plants of Each Wetland Status on a Scale from
0 to 1 ......................................................................... 7-49
7.11 Frequency of Occurrence of Vegetative Structural Categories (Canopy,
Subcanopy, Shrub and Vine Species) in the Understory of Constructed
Forested W etlands.................................... 7-57
7.12 Soil Characteristics of Constructed Forested Wetlands, Including Mehlich I
Extractable N utrients .............. ............................. ............. ............... 7-59
7.13 Available (KC1 Extractable) NO3-N and NH4-N in Constructed Forested
W wetlands ............................................................... ...........................7-62
7.14 Species Codes for Canopy and Subcanopy Species Found in Natural
Wetland Communities in Florida...................................... .... 7-82
7.15 A Comparison of Chronological Age and Forest Successional Status in
Constructed Forested Wetlands ...................................... 7-101
xxvi
CHAPTER 5
CHARACTERISTICS OF CONSTRUCTED HUMMOCKS
IN CREATED WETLANDS
E. Tim Gysan, Susan Carstenn and John Baker
INTRODUCTION
HISTORICAL PERSPECTIVE
Microtopographic relief plays an important role in many wetland ecosystems.
Microtopographic land surface variation causes conditions not found in flat landscapes,
including variable hydrology, soil conditions, and wildlife habitats. Hummocks are one
type of microtopography caused by natural events in wetlands. Hummocks form from
organic matter accumulation around standing trees, brush, and wind-thrown trees (Hardin
and Wistendahl 1983). Wetlands in the Canadian north contain hummocks formed by
differential erosion (Munro and Shaw 1997), soil uplift by pressure created by the
migration of the freezing interface towards permafrost inside mounds (Crampton 1977),
and the upward displacement of soil caused by freeze-thaw of ice lenses (Mackay 1980).
Hummocks can form by channel erosion and soil deposition in rivers and river deltas.
One example of this phenomenon is the collection of large hummocks at Otter Island in
St. Helena sound along the coast of South Carolina (South Carolina DNR and others
1996).
Wetland hydrologic conditions are the major influence on freshwater wetland
structure and function. Hydrology directly affects biota through hydroperiod and depth of
inundation. Hydrology indirectly affects biota by changing soil conditions such as
nutrient availability, oxygen content, and pH. Wetlands are the transition between
terrestrial and open water ecosystems and thus contain many species found in both
systems. Small changes in hydrology can have great influence on the vegetation found in
the wetland (Mitsch and Gosselink 1993). Conner and others (1981) suggest that flooding
regime is an important controlling factor on vegetation, based on work in swamps in
Louisiana. Joseph Hmielski (1994) found that in the hummocky transition and forest
zones of flat transects occupying low elevations along brackish marsh-upland continue at
the Virginia Coast Reserve/LTER, hummocks appear to allow glycophytic vegetation to
colonize closer to the tidal creek thus increasing the width of transition zones. The effect
is caused by the control of topographic variation, in the form of land slope and
hummocks, on the position of vegetation zones through its effect on physiochemical
variables.
The unique conditions found on hummocks can increase diversity within other
natural wetlands (Vivian-Smith 1997). Hummocks favor seed germination and
establishment of diverse vegetation including tree species (Titus 1990). Huenneke and
Sharitz (1986) found that tree seedlings in natural and disturbed swamps were more
likely to occur in areas of stabile substrate where they were able to escape inundation.
Seedlings were much less dense in areas of unconsolidated soils with complete
inundation during the growing season. Kozlowski (1984) showed that tree species are
much more sensitive to environmental variations (such as water level fluctuations) as
seedlings than they are as adults. Water most likely becomes a limiting factor in
bottomland tree survivorship only on sites continuously flooded for long periods of time
during the growing season (Hosner 1960). Lowry (1994) found that in swamps with
flooding during more than 35% of the growing season, woody plants are restricted to
mounds (hummocks). These studies have shown that varying hydrology and unique soil
conditions created by microtopographic variations are valuable within a forested wetland.
SITE INFORMATION
The initial goal of this project was to incorporate microtopography, in the form of
hummocks, into one or more constructed wetlands and to study the change in the
hummocks over time, soils, vegetation, and hydrology to assess the effects on the
wetland. Two reclamation projects were found and hummocks incorporated into their
design. A final mature site, with constructed hummocks, served as a comparison to the
immature sites. Figure 5.1 shows the location of the sites.
Agrifos L.L.C. and Janine Callahan, the reclamation coordinator for Agrifos,
incorporated microtopography into the design of a current reclamation project. Eighteen
hummocks were constructed; nine hummocks approximately 4m x 2m x 0.6m (length,
width, and height) and nine hummocks approximately 4m x 2m x 0.9m. Hummocks
were placed in-groups of three, with each group having one hummock constructed from
each soil type. Soil materials used were sand tailings, mine overburden, and organic
compost made from recycled yard waste in Sarasota. One pop ash (Fraxinus caroliniana)
and one sweet bay (Magnolia virginiana) were planted on each hummock. No other
vegetation was planted on the hummocks. Monitoring began after the site construction
was completed in late March 1999 to establish baseline data for each hummock. Further
monitoring took place bi-monthly. The site plan for the Agrifos wetland, including the
hummock location and the hummock layout as constructed in the wetland, is shown in
Figure 5.2.
Cargill Fertilizer, Inc. and reclamation coordinator Rosemarie Garcia also
incorporated hummocks into a constructed wetland. Twelve hummocks were built in the
wetland, half using mine overburden and half using harvested muck. Hummocks are
approximately 6m x 6m x 0.9m. Sand tailings were not used in this project. Construction
was completed in September 1999. One green ash (Fraxinus caroliniana), one sweet bay
(Persia borbonia), and one bald cypress (Taxodium distichum) were planted on each
hummock. No other vegetation was planted on the hummocks. Monitoring began in
September 1999 and took place bi-monthly. The site plan for the Cargill Phase 7
reclamation is shown in Figure 5.3 along with the hummock placement and layout.
tI am
"A l 5p mngs
,- eus1AP-
W .NJWIn Is --. a ~ I n R 1*-
l e .S.prne l. r P.. ay
Holidev -- 23r"
Irnm H-h-' e la d" I.nsr y D
G1 La an -" "-" :
ad. l t rlnff I P4 'D wa 3 n'',
Treasure Isian i St Pete urg 1 de --s
PMt.r C e Y on Pm
01909 MapQustoomn. Inc- Laieo
Figure 5.1. Constructed Wetland Site Locations.
Figure 5.2. Agrifos Wetland As-Built Construction Plan with Location and Layout
of the Constructed Hummocks.
5-4
Tvoical Hummock
#
- hummock number
= hummock soil type
n quadrat number
Soil Types
0 = overburden
M muck
/
12 10
.8
12 10 8 6
M 0 .9 M .7 0
11 9 7
0 M 0
4
.6 M .3
5 3
M .5 0
PASIURELAND (210) 90 oc.
OEN WATER (520) 177 ac.
wIXE mnfo AND FOREST (630) 25 oc.
IHFRIACErIS Al1 AND (640) = _i 9u .
TOTAL ACRES J41 oc.
IIICIt WAIER = 126,5 ngvd
NORMAL WAIER 125.5 ngvd
lOW WA 'ER )24.5 ngvd
Bare Rool BuWler ac.
~,w/ J emoni fr 200 I*/o r)
thctllr Ulk tud Items ..9 tsc.
(po eveme. A, 100 tm lm/aI
Figure 5.3. Cargill Fertilizer, Inc. Phase 7 Wetland Map Showing Hummock
Location and Layout.
2 .2
O
0
M
N.T.S.
Ted Goodman at Iluka Resources in Green Cove Springs allowed hummock
studies done in a reclaimed titanium mine site. The site was reclaimed in May 1993 and
contains constructed hummocks made by topsoil replacement. The hummocks are not
uniform in size.
The five hummocks randomly selected for the study range in size from 4m x 3m x
0.6m to 6.5m x 4m x 0.6m. The site has been deemed successful and released by the
United States Army Corps of Engineers and the Florida Department of Environmental
Protection. Cypress trees (Taxodium distichum) from the company's nursery were planted
on each hummock. The site has a high density of herbaceous understory vegetation on the
hummocks. The Site 7 wetland is shown in Figure 5.4 along with the study hummock
location.
PURPOSE
Previous projects conducted on behalf of the Florida Institute of Phosphate
Research by Mellini Sloan (1998) and Benjamin Bukata (1999) studied microtopographic
relief in natural wetlands and its development in reclaimed wetlands. The preliminary
work on the development of microtopography in the previous projects suggests that
construction of hummocks may significantly increase tree growth and understory
vegetation. The next step is to evaluate the design of relief and the contributions that
relief can have in constructed forested wetlands. That evaluation was the purpose of this
project.
Ultimately, the goal of this research was to understand the both methods of
incorporating hummocks into constructed wetlands and the role they have in the
enhancement of vegetation growth, vegetation survival and vegetation diversity, as well
as hydrologic function.
Construction of hummocks in created wetlands requires consideration of the soils
to be used, the size and shape of the hummock, and the height of the hummock peak
above the water table. In this study, to understand structural characteristics of hummocks
of varying sizes and soil composition, soil moisture and surface elevation were measured
on each hummock. This study was set up to find trends between soil moisture conditions,
changes in the hummock structure over time, facilitation of tree establishment and
growth, and richness of species colonizing each hummock.
To determine the effects of standing water on hummock conditions, water level
was correlated with soil moisture. To show the species richness each hummock type can
support; species colonization was recorded. To document the role of hummocks in tree
growth and survival, tree saplings were monitored to track establishment and growth both
on and off the hummocks.
Lc
4I
Center Stake
t12
3
sITE 7
TOPOGRAPMC CONTOUr
INUNDATION ZONE
NORTH
ii a-Sj
Figure 5.4. Iluka Resources Site 7 Wetland Map with Hummock Location and
Layout Shown.
METHODOLOGY
HUMMOCK ELEVATION MEASUREMENT
Establishment of Benchmarks
A benchmark was established in the Agrifos site by driving a 5-foot long (1.5m),
/4-inch (0.64 cm) steel rebar into the ground at a central point between the hummocks
after construction. Four-foot (1.2m) lengths of -inch (0.64cm) steel rebar were driven
into the center of each hummock leaving a six-inch section above ground. Elevations,
based on a surveyors benchmark elevation, were taken at the top of each rebar by
surveyors during the as-built site survey. Benchmarks were established in the Cargill site
using 5-foot (1.5m) lengths of -inch (0.64cm) steel rebar. Rebar was driven into the
center of each hummock leaving 1-foot (30.5cm) of rebar exposed above ground.
Elevations were taken at the top of each rebar relative to the surveyors' benchmark. No
benchmark was established in the Iluka site, as survey information was not available.
Elevation Measurements
A tape measure was stretched across the length and width of each hummock
horizontally from the center rebar to establish major and minor transects along the
centerline. A typical hummock with transects is shown in Figure 5.5. Stake flags were
placed at 30.5cm intervals to serve as permanent sampling locations in the Agrifos and
Iluka wetlands. Permanent sampling locations were set up at 61cm intervals in the Cargill
wetland because of larger hummock sizes. Heights were taken with a laser level placed at
the benchmark point between the hummocks. The readings were given in feet and inches
to the nearest tenth of an inch. Height measurements were taken at each sampling point.
Height was also taken at the top of each rebar to provide a relationship with the
benchmark elevation relative to mean sea level (MSL).
The top of the rebar was considered the zero point. Each hummock height was
subtracted from the height at the top of that hummock's rebar to give a difference in
height in feet at each point. The difference in height was subtracted from the known
elevation at the top of the rebar to get the elevation above sea level. Elevation versus
distance was then plotted using the Excel 97 spreadsheet.
Cross sectional areas along the major and minor transects were generated for each
hummock (Figures A1-A35) by using multiple applications of Simpson's 1/3 Rule and
Simpson's 3/8 Rule (Chapra and Canale 1988).
Tree
Off-Hummock Quadrat
Location
Sampling Point
Figure 5.5. A Typical Hummock with Major and Minor Transects Shown as
Flagged Sampling Points. Major Transects Cover the Length of
the Hummock. Minor Transects Cover the Width of the Hummock.
5-10
Simpson's 1/3 Rule -
I = (b-a)[(f(xo) + 4Xf(xi) +2Ef(x2)+f(xn))/3n] [1]
I = area under the cross section curve
a = length at x = 0, tip of hummock
b = length at x = n, end of hummock
f(xo,1,2,n) = value on y-axis, height of hummock
xl = the odd number points
x2 = even number points up to but excluding xn
n = number of points
Simpson's 3/8 Rule
I = (b-a)[(f(xo) + 3f(xi) +3f(x2)+f(x3))/8] [2]
I = area under the curve
a = length value at x = 0, tip of hummock
b = length value at x = n, end of hummock
f(x0,1,2,3) = value on y-axis, height of hummock
The change in area during each measurement period was used to calculate the
percent change in hummock elevation. Percent change in area was determined by
subtracting the new area from the original area and dividing the result by the original
area.
Change in Area
% Change = (Ao -A1)/Ao [3]
Ao = original area
Ai = new area
Cross sectional areas calculated for each hummock were compared to the original
value to find changes over time. The changes indicate the amount of degradation in the
hummock surface.
WATER LEVEL MEASUREMENT
Water level was recorded to relate the soil moisture in each hummock with the
height of the water relative to each hummock. Stevens Type F water-level recorders
Model 68 were installed in the Agrifos and the Cargill wetlands. Data were not collected
during the first growing season however, because the recorders were not installed until
mid-October. Water levels were determined by taking height readings at multiple points
along the edge of the standing water. Elevations of the water surface were then
determined using the same process as for hummock elevations.
5-11
SOIL MOISTURE MEASUREMENT
Soil moisture readings were taken using a TH20 soil moisture meter. Readings of
soil moisture were taken at each sampling point along the major and minor transects.
Three outputs are possible with the TH20 meter: direct output voltage, organic moisture,
and mineral moisture. Direct probe output was used because of greater ease of calibration
for specific soils.
Calibration curves for specific soils are based on the relationship between the
dielectric constant (s) sensed by the probe and the water content (0). Specific calibration
curves for each hummock soil type can be created. Soil moisture was calculated from the
voltage read by the probe. Voltage (V) was related to s by the following equation:
'ls = 1.07 + 6.4V 6.4V2 + 4.7V3 [4]
&s = square root of dielectric constant
V = voltage
The actual soil moisture was then calculated from the following equation
(coefficients described in user manual):
0 = [Is ao] / al [5]
0 = volumetric water content (m3/m3)
ao = dry soil coefficient
a, = wet soil coefficient
A generalized curve for 0 versus V is provided in the user manual and provides a
typical error of 0.05 m3/m3. The coefficients for wet and dry soil are based on these
curves. Perfect calibration decreases error to 0.02 m3/m3. Calibration was not done for
this project because the trends seen in water content are more important to the hummock
comparison than true values. The tendency of soils to compact and shift in the new
wetlands changing the pore spaces prohibits accurate calibration. Water contents were
taken on a bi-monthly basis throughout the growing season.
TREE MEASUREMENT
Tree heights were measured with a standard tape measure. Heights were taken
from the base of the tree to the highest point of the tallest branch. Heights were taken to
the nearest 0.3cm. Basal diameter was measured using standard calipers. Diameters were
taken to the nearest millimeter. Tree measurements were taken for 18 trees of each type
planted on the hummocks in the Agrifos wetland. Nine trees of the same species off the
hummock were originally supposed to be sampled to compare growth and survivorship
with on hummock trees. However, only five ash trees were ever found off the hummocks,
and no sweet bay trees were ever seen. These trees were measured at the beginning and
end of the growing season. Due to the late construction of the Cargill wetland, only initial
5-12
measurements were made of the 12 trees of each species on the hummock. Two ash, five
bay, and five cypress trees were found off the hummocks. Tree measurements at the Iluka
site were limited to diameter at breast height due to the extreme height of the trees.
Height was not estimated for these trees.
VEGETATION MEASUREMENT
No species were initially planted on the Agrifos or Cargill hummocks to observe
colonization. Plants were identified, and a percent cover for each species within a 0.25m2
circular quadrat was given. Four quadrats on each hummock were counted during each
sampling period. Two quadrats were placed along the top of the hummock in lower
moisture condition, and two were placed along the slope of the hummock at the soil/
water interface. Quadrats were placed in similar places on each hummock. Quadrats were
placed at 18 points off the hummocks in the Agrifos wetland, 12 points in the Cargill
wetland, and five points in the Iluka wetland to compare vegetation in differing growing
conditions. Off hummock quadrats were randomly located. Quadrat sampling points were
marked with 30.5cm sections of PVC pipe on the hummocks and with 90cm sections of
PVC off the hummocks. The numbers of species (s) were counted as a simple diversity
measurement. The percent cover (Ci) for each species (Brower and others 1990) within
the quadrat was determined.
Percent Cover- Ci = ai / A 100 [6]
ai = total area covered by a species
A = total area sampled
The richness and relative coverage was correlated to show the value of each species in
the hummock community. The Shannon diversity index (Brower and others 1990) was
used to determine diversity as each quadrat is considered a random sample of the entire
community.
Shannon Diversity Index- H' = -Zpi*logio (pi) [7]
H' = Shannon diversity
pi = n/N
N = number of individuals total
ni = number of individuals in a given species
Because understory vegetation was not sampled by individual, relative coverage was used
to determine pi by calculating the probability a species would be sampled in a quadrat.
Weighted Probability pi = P/ P [8]
where P = ni/n
P = probability a species will be sampled
n = total number of quadrats
ni = number of times a species is sampled
5-13
An evenness index was also calculated to provide a truer idea of the vegetation found on
each hummock.
Shannon Evenness J' = H'/H'max [9]
where H'max = log s
H'max = maximum Shannon diversity
J' = evenness of species distribution
s = number of species
Community similarities were calculated for habitat on and off the hummocks. The
Sorensen coefficient of community similarity (CCs) was used for comparison because of
interest in only the presence or absence of species (Brower and others 1990).
Sorensen Coefficient CCs = 2c/(si + s2) [10]
c = number of species similar to both communities
sl = number of species in community 1
S2 = number of species in community 2
PHOTOGRAPHIC RECORD
A photographic record has been kept of the Agrifos wetland system starting at
construction. Bi-monthly pictures were taken from permanent photo stations marked in
the wetland. A 1.5m section of PVC pipe was placed in the wetland next to the
benchmark point and at similar position between the last 9 hummocks. All photos from
within the wetland were taken from that five-foot height. Photos include images of each
group of three hummocks and from a point elevated above the wetland. Similar
photographic records were kept for the Cargill and Iluka sites.
5-14
RESULTS
HUMMOCK-TO-HUMMOCK COMPARISON
Change in Cross-Sectional Area
The change in cross-sectional area of each hummock measured along the major
and minor transects was intended to show the amount of erosion or settling in each soil
type used in hummock construction. Figure 5.6 shows the percent change in cross-
sectional area for the hummocks in the Agrifos wetland. The changes shown are averages
for each hummock type. A decrease in percent change from the first sampling period to
the last sampling period indicates a continued soil shifting throughout the first growing
season after construction. The hummocks constructed from organic matter show the
largest decrease in cross-sectional area along both the major and minor transects. By the
last sampling period (1999), the organic hummocks showed a change around -6.00%
from the original height. Overburden hummocks were next, with a change of around -
4.00%. Sand hummocks showed the least amount of change with a shift of -2.50%.
Sampling during the summer of 2000 revealed continued decreases in cross-sectional
area. Organic hummocks still showed the greatest decrease at -16.0%. Sand hummocks
showed an average decrease of slightly greater than 6.0%. Although still decreasing in
cross-sectional area, the magnitude of the change decreased in overburden hummocks
(less than -2.0%).
Figure 5.7 shows the percent change in cross-sectional area for the Cargill
wetland. After the first season, there was little difference between organic and
overburden hummocks. After the second season, there appears to be larger decreases in
overburden hummocks than organic hummocks. This is particularly apparent along the
minor transect.
Figure 5.8 shows percent change in cross-sectional area for the Iluka Resources
wetland. This mature site has hummocks constructed only from overburden. These
appear to show a slight increase in area by the end of the growing season. Along the
major transect, the increase is about 1.00%. Along the minor transect, the increase is
around 4.00%. The purpose of this figure is to that show after the initial negative shifting
of the hummock soil seen in above figures, a growth or stability of the hummock occurs.
Species Diversity
Species diversity indices were intended to show the differences in the ability of
hummocks to support understory vegetation. Table 5.1 shows the species diversity as a
simple species count and as a Shannon index for each hummock type and each sampling
period. Included is a percent cover of vegetation on the hummocks. In the Agrifos
wetland, the overburden hummocks have the highest number of species during the first
5-15
10%
8%
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
-12%
-14%
-16%
-18%
-20%
Sand Tailings Organic
Hummock Type
Overburden
o Major 4/23 M Major 5/19 E Major 8/5 I Major 10/13 E Major Sum 2000
(b)
m 5%
.2
0 -5%
_c
c -10%
.,
u
S-15%
0)
-20%
Sand Tailings Organic Overburden
Hummock Type
O Minor 4/23 M Minor 5/19 B Minor 8/5 B Minor 10/13 0 Minor Sum 2000
Figure 5.6. Changes in Cross-Sectional Areas for (a) Major and (b) Minor Transects
in the Agrifos Wetland. Standard Error Bars Are Calculated Using the
Excel 97 Chart Wizard.
5-16
10%
8%
6%
4%
2%
0% -
-2%
-4%
-6%-
-8% -
-10%
Organic Overburden
SMajor 11/1 Major 6/2/00
(b)
10%
8%
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
Organic
Overburden
0 Minor 11/1 [ Minor 6/2/00
Figure 5.7. Changes in Cross-Sectional Areas for (a) Major and (b) Minor Transects
in the Cargill Wetland. Standard Error Bars Are Calculated Using the
Excel 97 Chart Wizard.
5-17
r--^-----------
10%
8%
6%
4%
2%
0%
-2%
-4%
-6%
-8%
-10%
Top Soil
O Major 8/31 I Major 10/20
(b)
10%
8%
6%
4%
0%
-2%
-4%
-6%
-8%
-10%
Top Soil
O Minor 8/31 E Minor 10/20
Figure 5.8. Changes in Cross-Sectional Areas for (a) Major and (b) Minor Transects
in the Iluka Resources Wetland. Standard Error Bars Are Calculated
Using the Excel 97 Chart Wizard.
5-18
N-I (D I It 'o r- Tn wo rN
N- C4 0,) MN C44 In'" (N M r r-- 'Ia-
,-. 00 oo C o o o o 0
00 N 00 00 O ON C 00 O N 00
'-16 66666666666
Co0 0 'o 0 oIn 0 W M D n
o0 -------- -
~466 0 0 0 ~ 6
004o N r- o .0 O\ ON 0 r'm Wi 0
.-l ~ r ,l t -l Nl -^ M
N- "T rif 1o .o o
00 00 0 C4
0000 N 000 oa o
0 0 0 'N .0
wodome
enC en
m o m^ord
00 C A C 00 00
S5 B 58 a
00,i0)i00ci0 000000
o\ C\
a\ o\
- -
ON -
C) *C)
cO co
C. Cu
5-19
00 ,n 'V 0
ONOO
oo o\ o\
00 ON ON
o o
m-
[-.. -.. ..
two sampling periods with 17 and 19 species recorded. The overburden hummocks also
have the highest Shannon diversity and evenness during the first two sampling periods
with 1.06 (0.86) and 1.15 (0.90). The organic hummocks have the lowest number of
species and the lowest Shannon indices for the first two sampling periods. At the last
sampling period of 1999, the sand hummocks have the highest number of species (19)
and highest Shannon index (1.17). While organic hummocks generally had lower
diversities, they had the highest percent cover during the last two periods with 90% and
56% cover. Overburden hummocks had higher percent cover than sand hummocks in
each sampling-period of 1999. High diversity with low percent cover indicates that, while
a soil type may have conditions suitable for many different plants, not many are actually
growing. The Cargill wetland has a higher number of species growing on the organic
hummocks (13 and 19) than on the overburden hummocks (10 and 13). The organic
hummocks also show a higher Shannon diversities during both sampling periods and
have higher percent covers. The mature Iluka site, having topsoil hummocks, has the
highest overall number of species (21) and the highest Shannon diversity (1.19). The
Iluka hummocks had a percent cover above 35% for each sampling period.
Species richness was greater on overburden and sand hummocks than on organic
hummocks. Both, diversity and evenness were greater on the sand and hummocks than
on organic hummocks. However, percent cover was greatest on organic hummocks.
Tree Growth
Tree growth and survivorship provides an indication of the potential for
hummocks to be used as planting sites for tree seedlings within a wetland. Figure 5.9
shows the survivorship of tree seedlings within the Agrifos wetland. Every tree seedling
survived the first growing season on the overburden hummocks. Only one tree died on
the sand hummocks, a Magnolia virginiana. The organic hummocks had the lowest
survivorship, with only one Fraxinus caroliniana and two M. virginiana living the entire
growing season.
Figure 5.10 shows the changes in height and basal diameter for the trees planted
on hummocks in the Agrifos wetland. Among the F. caroliniana, trees planted on the
sand hummocks had the highest growth for both height (5% increase) and basal diameter
(28% increase). Overburden hummocks had the next highest growth with height increase
of 5% average and diameter increase of 21%. Sand hummocks, again, had a higher
increase in basal diameter for M. virginiana with growth of 6%. Overburden hummocks
had the highest increase in tree height at 5%.
Tree growth data from the 2000 field sampling season is not included because tree
survival was minimal in the Agrifos wetland with only one tree surviving. This is
attributed to severe drought conditions. In the Cargill wetland, more trees were found on
the hummocks in 2000 than were planted in 1999. None of the trees was small enough to
suggest natural recruitment. With no record of their planting, it was impossible to
analyze tree growth at this wetland.
5-20
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
sand organic overburden
0% Ash 0% Bay
Figure 5.9. Percentage of Trees Surviving After One Growing Season in the Agrifos
Wetland. Six Trees of Each Species Were Originally Planted for Each
Hummock Soil Type.
5-21
_ ___I
Sand
Organic
Hummock soil type
SHeight EDiameter
(b)
Overburden
Sand Organic Overburden
Hummock soil type
OHeight Diameter
Figure 5.10. Changes in Tree Height and Basal Diameter for (a) Fraxinus caroliniana
and (b) Magnolia virginiana. Measured on the Hummocks at the
Beginning and End of the Growing Season in the Agrifos Wetland.
5-22
30%
25%
20%
15%
10%
5%
0%
-5%
-10%
I
30%
25%
20%
15%
10%
5%
0%
-5%
-10%
7-
LNW"9
I
I
I
Volumetric Water Content
Volumetric water contents (one expression of soil moisture) of hummock soils
can be used as an indication of the available microhabitats for vegetation growth. Figures
5.11-5.15 have the volumetric water content plotted against hummock elevation for each
soil type in the Agrifos wetland for each sampling period. A best-fit line has been drawn
through each group of points, and an r2 value determined. A steeper slope of the best-fit
line indicates a higher range of moisture values from the highest elevation to the lowest.
In each sampling period, the organic soils have the steepest slope and therefore the
highest range of moisture from the lowest to highest elevation. Overburden hummocks
appear to have the shallowest slopes, indicating a more even distribution of moisture
from lowest to highest elevation. From the first to the last sampling period, the r2 values
steadily increase for each soil type throughout 1999. Organic soil values increase from
0.58 to 0.87. Sandy soil values increase from 0.37 to 0.88. Overburden soil values
increase from 0.33 to 0.92.
Figures 5.16, 5.17 and 5.18 show the volumetric water contents plotted against
elevation for the hummocks in the Cargill wetland. The organic soils and overburden
soils have similar slopes, indicating close ranges in moisture values. The increasing r2
values are again seen for these soil types in 1999. The organic values increase from 0.35
to 0.75, and the overburden values increase from 0.47 to 0.81.
Figures 5.19-5.23 show the average volumetric water content for each hummock
in the Agrifos wetland. The maximum and minimum values for volumetric water content
are also plotted to show the range of micro-sites. A line has been drawn connecting the
average values to show the trend for each soil type. Figure 5.19 presents data from the
first sampling period. The organic hummocks, plotted in the middle of the graph, have
higher averages and wider ranges of water contents than overburden and sand hummocks.
Overburden hummocks have higher averages than the sand hummocks. The overburden
hummocks also appear to have a similar width of ranges as the sand hummocks, but with
higher minimum and maximum values. The same trend appears in each of the next three
figures, which contain data for the other sampling periods.
Figures 5.24. 5.25 and 5.26 show similar data from the Cargill wetland. Again,
the trend shows organic hummocks to have higher average volumetric water content than
the overburden hummocks. Organic soils also have a wider range of values than the
overburden soil, indicating more available micro-sites for vegetation.
HUMMOCK TO OFF-HUMMOCK COMPARISON
Species Diversity
The ability of hummocks to provide microhabitat for vegetation growth not found
in other areas of a wetland would be a major attraction of incorporating hummocks into
5-23
Sand Hummocks
2 = 0.37
r =0.37
97 97.5 98 98.5 99 99.5
Organic Hummocks
97 97.5 98 98.5 99 99.5 100
2
r =0.59
100.5
r = 0.34
Overburden Hummocks
97 97.5
98 98.5
99 99.5
100 100.5
Elevation (ft. MSL)
Figure 5.11. Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on April 23, 1999, in the Agrifos Wetland.
Water Level Measured at 96.94 Ft. MSL.
5-24
O
0~I )
Sand Hummocks
0 l~,
~C- -
T -I
97.5
Organic Hummocks
0+
. 0
gO Ss:.
97 97.5
98 98.5
99 99.5
Overburden Hummocks
97 97.5
98 98.5
99 99.5
100 100.5
Elevation (ft. MSL)
Figure 5.12. Volumetric Water Content Graphed Versus Elevation for Each Sampling
Point on May 19, 1999, in the Agrifos Wetland. Water Level Measured at
97.28 Ft. MSL.
5-25
99.5
2= 0.59
r = 0.59
100.5
r2 = 0.34
0.4
0.3 -
0.2 -
0.1
0
S.. 7 ~ *
0, 2
r2 = 0.37
Sand Hummocks
r2 = 0.86
A*. %g
S:i-
S~
99.5
, Organic Hummocks
*0
S
0
* -
97.5 98 98.5 99
Overburden Hummocks
97 97.5
98 98.5
99 99.5
Elevation (ft MSL)
Figure 5.13.
Volumetric Water Content Graphed Versus Elevation for Each Sampling
Point on August 5, 1999, in the Agrifos Wetland. Water Level Measured
at 97.33 Ft. MSL.
5-26
0.6
0.5
0.4
, 0.3
0.2
0.1
4
97.5
0.6
0.5
0.2
0.1
0
* *
2
r =0.81
99.5
r = 0.75
0.7 -
* 0.6
o 0.5-
|ti0.4-
S0.3 -
| 0.2
> 0.1
>
100.5
(a)
Sand Hummocks
97.5 98 98.5 99
r = 0.87
0 *
* Se
* 0
97.5 98
(c)
Overburden Hummocks
S.*
S i
97.5 98
Elevation (ft MSL)
Figure 5.14. Volumetric Water Content Graphed Versus Elevation for Each Sampling
Point on October 13, 1999, in the Agrifos Wetland. Water Level
Measured at 97.42 Ft. MSL.
5-27
0
0
S0.89
r = 0.89
0
U
8 E
B
>
98.5
I 0.6-
0
1 0.5-
I-
S0.4
0.3 -
0.2-
o
> n -
2= 0.92
r = 0.92
I I I I I I
* -. >-
^ .....
2
r = 0.80
0 *
Og I -u
0. pg0.
6)1
o
S0.5
S0.4-
O 0.3
0.2
0.1
o 0
97
"S 0.8
- 0.7
S 0.6
o 0.5
0.4
S0.3
0.2
'* 0.1
| 0
> 96
97.4 97.6 97.8 98 98.2 98.4 98.6 98.8 99
(b)
r = 0.55
*0
* -,** *.
? %-I -
97 97.5 98
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
97 97.5
r2 = 0.80
0
** *
* *
98 98.5
99 99.5
Elevation (ft MSL)
Figure 5.15. Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point During Summer 2000 in the Agrifos Wetland.
Water Level Measured at 97.52 and 98.15 Ft. MSL.
5-28
1.2
so*
5.5
100.5
(a)
Organic Hummocks
0.7
0.6
-
0.5
S0.4 -
60.3
|o.3-
0,1
I 0.1 -
0
0 ~
Og 0 *
0
0
0.
0
* **
SI I I I I
126 126.5
127 127.5
Elevation (ft MSL)
(b)
Overburden Hummocks
* ** *
*
"* /^^-o.- ** ,*
*:. **
0 :0.0,.
125.5 126 126.5
127.5 128
Elevation (ft MSL)
Figure 5.16. Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on September 13, 1999, in the Cargill Wetland.
Water Level Measured at 125.15 Ft. MSL.
5-29
2= 0.35
r = 0.35
0 0
0 *0
0
0 .0
124.5
125.5
0.7
-0.6
00.5
60.4
P0.3
'0O.2
00.1
2
r =0.47
124.5
I
+ 4
(a)
Organic Hummocks
0.7 -
0.6-
-
0.5
i -5
0.4 -
0.3-
0.2-
> 0.1-
126 126.5 127
Elevation (ft MSL)
(b)
127.5 128
2= 0.82
r = 0.82
125 125.5 126 126.5
127 127.5 128
Elevation (ft MSL)
Figure 5.17. Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on November 1, 1999, in the Cargill Wetland.
Water Level Measured at 125.88 Ft. MSL.
5-30
*~
S4
0
2 = 0.75
r = 0.75
S
0
0
0
* *
125.5
124.5
0.7
S0.6
0.5
S0.4
S0.3
u 0.2
S0.1
04--
124.5
I ( I I I 7 _
Organic Hummocks
*
<* 0
0 *s* '&e *
~ 0
S 0
06*
oil 0
*
* .
125 125.5 126 126.5 127
127.5 128
Elevation (ft MSL)
(b)
Overburden Hummocks
0 0
S
0
. ** .*o
o# *
124.5
125 125.5 126 126.5 127 127.5
Elevation (ft MSL)
Figure 5.18. Volumetric Water Content Graphed Versus Elevation for Each
Sampling Point on June 2000 in the Cargill Wetland.
Water Level Measured at 125.62 Ft. MSL.
5-31
2
r =0.73
124.5
2
r =0.68
0.7 -
0.6-
0.5
S0.4-
e
0.3
-5
" 0.2
S0.1-
4
% N< .a
Ooqb r
..
U./
0.6
0.5
0.4
0.3
0.2
0.1
o 0 n 1
0
Hummock Type & Number
Figure 5.19. Values for Average Volumetric Water Content Plotted with Minimum and Maximum Values for Each Hummock
in the Agrifos Wetland on April 23, 1999.
0.6
0.5
0
| 0..4 -_---
P!
0.3 -
o
> 0.2-- -- --
0.1-- -
0 0o 0o < 0I < 4 4
o o o
Hummock Type and Number
Figure 5.20. Values for Average Volumetric Water Content Plotted with Minimum and Maximum Values for Each Hummock
in the Agrifos Wetland on May 19, 1999.
0.6
I 0.5
0
0.4-
0.3
o
> 0.2
0.1 .
0
Ir I' b N K
-, # "v 0*'-;
Hummock Soil Type and Number
Figure 5.21. Values for Average Volumetric Water Content Plotted with Minimum and Maximum Values for Each Hummock
in the Agrifos Wetland on August 5, 1999.
S0.4 -_
) 0.23-- -- ----
0.3
LC 0.2
0.1
Hummock Soil Type and Number
Figure 5.22. Values for Average Volumetric Water Content Plotted with Minimum and Maximum Values for Each Hummock
in the Agrifos Wetland on October 13, 1999.
0.7
0 .6 --------------------------------- -- -- --_ _---
^ 0.5 --------------------- -- -- -- --------------------
0.6
S0.5
0 -
0.4
0.3
0.2
0.1- -
0
Hummock Type & Number
Figure 5.23. Values for Average Volumetric Water Content Plotted with Minimum and Maximum Values for Each Hummock
in the Agrifos Wetland in Summer 2000.
0.6
0.5
o
U.
S0.4
0.3
S0.2 -
0.1
o3 ,-- o, o
0.1 -- -- -- -- -
o- o O o2 o)
Hummock Type and Number
Figure 5.24. Values for Average Volumetric Water Content Plotted with Minimum and Maximum Values for Each Hummock
in the Cargill Wetland on September 13, 1999.
10I
- m -
0
Hummock Type and Number
Figure 5.25. Values for Average Volumetric Water Content Plotted with Minimum and Maximum Values for Each Hummock
in the Cargill Wetland on November 1, 1999.
0.6
0.5
U
+ 0.4
o 0.3 -
> 0.2 --
0.1
0.1 -- -,--
0
Hummock Type and Number
Figure 5.26. Values for Average Volumetric Water Content Plotted with Minimum and Maximum Values for Each Hummock
in the Cargill Wetland on June 2, 2000.
constructed wetlands. Comparing species diversity on the hummocks to that found
elsewhere in a wetland provides information on the ability of hummocks to increase
vegetation diversity. Table 5.2 shows data for hummock and off-hummock species
diversity indices for the Agrifos, Cargill and Iluka wetlands. In each sampling period, the
number of species was greater on the hummocks than in the surrounding wetland areas.
At least 8 more species were found on the hummocks during every sampling period
except for the 9/13/99 sampling of the Cargill wetland where only 5 more species were
found.
Shannon diversities were greater on the hummocks in all sampling periods. In
every case except the first Cargill sampling, the Shannon diversity is considerably higher
on than off the hummocks. Data for Shannon evenness show a different trend. The
evenness is higher on the hummocks in the Agrifos wetland in each sampling period, but
is lower on the hummocks in the other two wetlands indicating a dominance by a few
species.
Percent cover was lower on the hummocks in the Agrifos wetland in each
sampling period. The same trend was found in the Iluka wetland for the first two
sampling periods. The third period percent cover on the hummocks was higher than off
the hummocks. Percent cover in the Cargill wetland was higher on than off the
hummocks in all sampling periods.
Community similarities between habitats on and off the hummocks are shown in
Table 5.3. Values can range between 0 and 1.0, with a value of 1.0 meaning that all
species are found in both communities. Values are shown for each hummock type versus
the off hummock community as well as for the hummock community as a whole versus
off hummock habitat. Values appear to get lower throughout the growing season possibly
following increasing water level. None of the Sorensen coefficients show a high amount
of similarity between the hummock and off hummock communities, as all values fall
between 0.25 and 0.7. The ranges indicate some similarity in the communities. Some
species are found both on and off the hummocks, but the majority are found in only one
of the two community types. Low community similarities also can indicate a large
difference in the species richness in the community types.
Tree Growth
The ability of hummocks two provide better growing conditions for tree saplings
than found in other wetland locations provides another reason why hummocks may be
valuable when incorporated into constructed wetlands. Table 5.4 contains data for trees
planted on and off hummocks in the Agrifos and Iluka wetlands. F. caroliniana growing
in the Agrifos wetland appear to be taller on the hummocks than off the hummocks in all
cases except for the one tree growing in organic soil. The trees planted off the hummocks
appear to be larger in basal diameter than those growing on the hummocks. Cypress trees
planted in the Iluka wetland show a clear trend in growth. Those trees planted on the
hummocks have a considerably larger DBH than the trees growing off the hummocks
(3.36 to 1.78 cm).
5-40
Table 5.2 Hummock and Off-Hummock Species Diversity Comparison for Agrifos, Cargill, and Iluka Wetlands.
Wetland Number of Shannon Diversity Shannon Evenness
Location Date Sampled Location Species (s) (H') (J') % Cover
Agrifos 5/19/99 on hummock 20 1.08 0.83 18
off hummock 11 0.85 0.82 21
Agrifos 8/5/99 on hummock 29 1.32 0.91 49
offhummock 18 1.09 0.87 53
Agrifos 10/13/99 on hummock 29 1.27 0.87 36
off hummock 16 1.04 0.86 58
Agrifos Sum2000 on hummock 41 1.38 0.86 51
off hummock 28 1.34 0.92 60
Cargill 9/13/99 on hummock 15 0.94 0.80 36
off hummock 10 0.92 0.92 18
Cargill 11/1/99 on hummock 20 0.98 0.75 51
off hummock 7 0.73 0.86 17
Cargill Sum2000 on hummock 52 1.53 0.89 86
offhummock 12 0.96 0.89 57
Iluka 5/4/99 on hummock 16 1.08 0.89 38
off hummock 8 0.87 0.97 52
Iluka 8/31/99 on hummock 21 1.19 0.90 45
off hummock 8 0.88 0.97 60
Iluka 10/20/99 on hummock 21 1.19 0.90 36
off hummock 11 0.98 0.94 28
Table 5.3. Community Similarity Between Hummock and Off-Hummock Species.
Wetland Community Number of Species Similar Sorensen
Location Date Sampled Type Species (s) to Off-Hummock Coefficient
Agrifos 5/19/99 sand 12 8 0.70
organic 8 4 0.42
overburden 17 5 0.36
all hummocks 20 8 0.52
off hummock 11
Agrifos 8/5/99 sand 16 8 0.47
organic 16 8 0.47
overburden 19 8 0.43
on hummock 29 12 0.51
off hummock 18
Agrifos 10/13/99 sand 19 10 0.57
organic 18 7 0.41
overburden 17 6 0.36
on hummock 29 11 0.49
off hummock 16
Agrifos Sum2000 sand 23 14 0.55
organic 15 9 0.42
overburden 30 14 0.48
on hummock 41 17 0.49
offhummock 28
Cargill 9/13/99 organic 13 6 0.52
overburden 10 7 0.70
on hummock 15 8 0.64
off hummock 10
Cargill 11/1/99 organic 19 6 0.46
overburden 13 6 0.60
on hummock 20 7 0.52
off hummock 7
Cargill Sum2000 organic 46 9 0.31
overburden 43 7 0.25
on hummock 52 9 0.28
off hummock 12
Iluka 5/4/99 on hummock 16 8 0.67
off hummock 8
Iluka 8/31/99 on hummock 21 5 0.34
off hummock 8
Iluka 10/20/99 on hummock 21 8 0.50
off hummock 11
5-42
Table 5.4. Average Values for Tree Parameters On and Off the Hummocks in the
Agrifos and Iluka Wetlands.
Agrifos Wetland Averages
Location Species Height (cm) Diam. (cm)
Sand Fraxinus caroliniana 58.00 0.74
Organic Fraxinus caroliniana 45.40 0.71
Overburden Fraxinus caroliniana 51.28 0.65
Off-hummock Fraxinus caroliniana 46.80 0.91
*data taken 10/13/99
Iluka Wetland Averages
Location Species Circum. (cm) Diam. (cm)
On-hummock Taxodium distichum 26.80 3.36
Off-hummock Taxodium distichum 14.18 1.78
*data taken 5/19/99
5-43
DISCUSSION
GENERAL
Analysis of the results yields only partial answers to the questions of which soil
type and hummock size are best and the value of hummocks in a wetland. The first thing
one must realize is that this study was designed to provide an overall picture of the
dynamics of hummocks, not provide specific information on why any one characteristic
behaves in a certain way. Those are questions to be answered by continued study. The
second thing one must realize when looking at these results is that they are for only one
growing season (only two months in the Cargill case). A long-term study would be
needed to get a clearer picture about what is really happening in the wetlands.
Conditions within a newly established ecosystem can vary greatly over a few
years. Weather varies slightly from year to year, some years being drier than others. A
dry year such as 1999 can have a dramatic effect on a wetland, especially a new wetland.
The Agrifos wetland, which was not manually flooded, depended solely on rainfall for its
water. Below average rainfall kept the wetland relatively dry. The dry conditions were
not conducive to establishment of wetland plants in the infant wetland. The Cargill
wetland did not experience the same dry conditions, as water was pumped into the
wetland. In an older site like the Iluka Resources wetland, periods of drought might not
have as big of an effect on the overall organization of the wetland. Ecosystems self-
organize over time until they adjust to the conditions characteristic of the region (Odum
and others 1997). The newly constructed wetlands are still beginning that process.
Though the wetlands are young and further study would be invaluable, that is not
to say nothing can be learned from this study. On the contrary, there is much valuable
information to be gleaned from the results of this study. Much can be said about both the
colonization of hummocks by vegetation and the ability of different soils to hold their
shape during early growth of the wetland. The ability of soils to hold moisture and
provide habitat for a wide variety of plants can also be seen. Data on overall tree growth
are limited because of the slow growth of trees, but survivorship during the early growth
stage can be tracked.
AGRIFOS
Three types of soil were used to construct hummocks in the Agrifos wetland. As
shown in Figure 5.6, the organic material used deteriorated the most during the first
growing season. Hummocks constructed from sand tailings held their shape the best. This
result is somewhat surprising due to the fact that sand tends to be more susceptible to
erosion than the other two soils (Thomas and others 1985) and the fact that sand
hummocks had the least percent cover of vegetation (Table 5.1). With little vegetation
growing, there was no root structure to hold the soil together. The organic hummocks had
a much higher percent cover of vegetation and thus likely much more root structure to
5-45
bind soils. Overburden hummocks fell in the middle in terms of changes in cross-
sectional area and percent cover.
There are several possible explanations for organic soils depleting more than the
others did, the most likely being decomposition. The organic material was made from
composted yard waste including grass and wood chips. Organic matter decomposes much
more quickly in the presence of oxygen than in anaerobic conditions (Reddy and Patrick
1983). With little water in the wetland, oxygen was readily available to the exposed
organic hummocks. The damp, warm, oxygen rich conditions allowed aerobic bacteria to
break down the organic matter, decreasing the cross-sectional area. Erosion of all
hummocks from climatic conditions such as wind and rain may have been limited
because of the extremely dry conditions occurring during this growing season. Falling
raindrops have enormous kinetic energy, which, when contacting soils, can cause
movement of particles leading to erosion (Sharma and others 1993). Without much
rainfall, there was little potential for weathering from precipitation. Wind erosion may
also have been limited due to lower than normal wind speeds, the relative close proximity
of the hummocks to the surface of the ground, and the growth of wind breaking
vegetation like Typha spp. and Sesbania spp. Particle size of the soils may have been too
large for movement by low speed wind. The possibility exists that the erosion seen in the
Agrifos wetland is typical for the soil types chosen for the hummocks. Continued study
would show how these soils react during the development of the wetland.
Based only on change in cross-sectional area, sand tailings hummocks appear to
be a good choice. However, having a pile of sand with nothing growing on it is not the
point of a hummock. Hummocks are supposed to provide conditions for vegetation
growth not found in other parts of a wetland. Availability of nutrients and soil moisture
contributes to determining vegetation growth.
Sand and overburden are both highly mineral soils. Mineral soils generally have
high nutrient availability, meaning plants can easily utilize any nutrients present in the
soil (Mitsch and Gosselink 1993). Sand tailings are likely to be very low in nutrients due
to their structure consisting almost entirely of sand grains. Overburden likely contains
some phosphorus as its structure includes clays, sands, and organic matter. The available
nutrients lead to higher vegetation growth on the overburden hummocks than on the sand
hummocks even with the lack of water. Ground water and surface water contributing to
the wetland would contain some level of phosphate due to the abundance of phosphate in
central Florida. The water level in the wetland was very low however, and likely
provided little nutrient to the hummocks. Organic soils can have low nutrient availability
because many nutrients are tied up in organic form. Plants require inorganic forms for
uptake and use in photosynthesis. Availability depends on the degree of decomposition in
the organic soil. More decomposition means more available nutrients. The rapid
decomposition of organic hummocks makes more nutrients available to plants, seen as
the high percent cover in Table 5.1.
Plants must also have available soil water for nutrient uptake and biological
processes. Organic soils have greater porosity and thus greater ability to hold water than
5-46
do mineral soils (Mitsch and Gosselink 1993). The results discussed from Figures 5.19-
5.22 clearly show that the organic hummocks have much higher average volumetric
water content meaning more available pore water. Sand has fewer pore spaces than
organic and overburden soils and contains the least amount of soil water. Overburden,
with its composition of sand, clay, and organic material, holds water better than sand,
making more available for plant uptake.
Organic hummocks show greater available pore water and in this case likely have
greater nutrient availability of nutrient (indicated by higher percent cover). Figures 5.11-
5.14 show that organic soils also have a wider range of micro-sites for plant growth. The
organic hummocks show lower species diversity and evenness. A few fast growing
species colonizing these hummocks likely are better able to uptake nutrients and out
compete other slower growing species. Overburden hummocks show greater ability to
hold soil water at higher elevation than do sand hummocks creating more available
micro-sites for plant growth. Overburden and sand hummocks show higher diversity than
organic hummocks. The same fast growing plants that can uptake readily available
nutrients are likely out competed in the lower nutrient situation by plants better able to
access nutrients.
Tree growth and survivorship is also related to soil moisture and nutrient
availability. The results of the tree study show that the growth of understory vegetation
may also have a large impact. Figure 5.9 shows that trees growing on organic hummocks
do not survive nearly as well as those on the sand and overburden hummocks. The
growth of understory vegetation on organic hummocks may have choked the trees by
using all available nutrient, water, and blocked most of the sunlight from the small tree
seedlings. The trees growing on the other hummocks showed an increase in basal
diameter and small increases in height. With lower nutrients and pore water, the likely
difference in survivorship and growth can be linked to the lack of competing understory
vegetation.
CARGILL
Overburden and muck were used to construct the hummocks in the Cargill
wetland. Figure 5.7 shows the muck hummocks fared slightly better than the overburden
hummocks in terms of soil erosion. The change was only seen between two sampling
periods, thus it is hard to see any trends developing. Both hummock types had relatively
high percent covers of vegetation (Table 5.1) whose root structure helps hold soil in
place. In contrast to the Agrifos wetland, the Cargill wetland was flooded by water from
other mining sites. Flooding the wetland had the added effect of surface water erosion on
the hummocks. Surface water movement caused by wind has the potential to carry away
soil particles causing undercutting along the sides of the hummocks. The wetland was not
flooded immediately, but gradually. Thus, the effect of surface water erosion was not
seen over the entire sampling period.
5-47
Flooding the wetland had the added effect of increasing the soil pore water in the
hummocks. Figures 5.24 and 5.25 show that the organic hummocks have higher
volumetric water content than the overburden hummocks as expected based on the
properties of organic and mineral soils. An increase in number of species, Shannon
diversity, and percent cover accompanied the increase in soil pore water. The water
pumped into the wetland likely had background levels of phosphorus, which were
utilized by the growing vegetation. The muck hummocks, which were exposed to
oxygen, would have added nutrients to the soil upon decomposition. The overburden
soils, because of their origin, also contain background amounts of phosphorous, which
plants could uptake as pore water increased. The muck hummocks likely had greater
diversity and percent cover due to more available nutrients and higher soil moisture.
Figures 5.16 and 5.17 show the two hummock types to have similar ranges of soil
moisture providing a similar distribution of micro-sites for vegetation growth. Organic
hummocks have higher values of soil moisture at similar elevations than do overburden
hummocks. This would be expected based on the characteristics of organic and mineral
soils.
Based on initial data, these two hummock soil types provide similar benefits in
terms of stability and colonizing vegetation. Tree data may provide the defining
characteristic when chosen between the two soil types. Due to the late construction of the
site during this study, only initial tree data were available and no comparison can be
made.
WETLAND COMPARISON
Comparing the hummocks in the Agrifos and Cargill wetlands becomes difficult
due to the difference in time of construction and the conditions found in each wetland.
Because the Cargill wetland was not completed until late in the growing season, only two
sampling periods of data were taken. These can be compared to the first two sampling
periods in the Agrifos wetland, but they occurred at opposite ends of the growing season.
The samplings taken at the end of the growing season can be compared, but the wetlands
are slightly different ages. In the early growth of the wetlands, the small age difference
could influence data. The difference in flood stage of the wetlands also makes
comparison difficult. Water level greatly influences soil moisture and nutrient
availability, which in turn affects the vegetation growing on the hummocks. None-the-
less, the comparison will be made between the two new wetland hummocks and the third
elder Iluka wetland hummocks.
The stability of the hummocks in the three wetlands begs the first comparison.
The hummocks in the Iluka wetland show a slight growth as opposed to the decay seen in
the infant hummocks in the other two wetlands. The soils in the older hummocks have
already undergone the period of settling and compaction, which takes place in newly
disturbed soils. The newly constructed hummocks in the Cargill and Agrifos wetlands are
still experiencing the settling, which accounts for some decay. The mature hummocks in
the Iluka wetland also have more vegetative root structure to provide soil stability than do
5-48
newly colonized infant hummocks. The data suggest that sometime between the
construction of wetland hummocks and seven years of age hummocks reach structural
equilibrium. Structural equilibrium refers to both soils having finished settling and
erosion and deposition being relatively equal. Buildup of organic matter may occur
causing the apparent growth in the Iluka hummocks. It should be noted that completely
accurate height measurement was made difficult by low lying tree limbs interfering with
laser level rod positioning. Drastic changes in the results due to the error are unlikely, as
extra time was taken to position the rod carefully for measurement. Comparing the
hummocks in the other two wetlands over the first two sampling periods shows that the
organic hummocks in the Agrifos wetland have more decay than the organic hummocks
in the Cargill wetland. Both have high percent cover of vegetation to bind soils. The big
difference is the composition of the soils. The Agrifos soils, being completely organic in
nature, likely decomposed faster than the sandy muck used in the Cargill wetland. The
overburden hummocks showed similar erosion, although differences were seen between
major and minor transects. Weathering patterns along the transects show differences due
to the direction of the prevailing wind and the direction of rainfall hitting the hummocks.
No comparison with the sand hummocks in the Agrifos wetland can be made as none
were constructed in the other wetlands.
Soil moisture values reflect not only the soil type, but also the level of surface
water in the wetland. Values for the hummocks in the Agrifos wetland increase as surface
water increases as do those in the other two wetlands. Comparing the soil pore water for
the different hummock types becomes tricky because the surface water level is different
in each wetland. The only accurate way to determine each soil's ability to hold water
would be by taking soil cores and running tests in laboratory conditions. The data
available from this study suggest that in flooded conditions (Figure 5.22, Figure 5.25, and
Figure A38), values are similar for the overburden hummocks in all three wetlands. The
values suggest that the composition of the overburden soils give them similar properties.
The organic hummocks in the Agrifos and Cargill wetlands show slightly different
averages with the Agrifos hummocks made of yard compost being higher. Based on the
origin of each soil type, this variation would be expected. Again, no comparison can be
made with sand tailings as only the Agrifos wetland had sand hummocks. It is interesting
to note the increase in r2 values for graphs of volumetric water content versus elevation in
each wetland. The trend suggests that, as hummocks age and equilibrium is reached, the
soil becomes uniform in its ability to hold pore water.
Vegetation growth on the hummocks shows that the mature Iluka wetland's
overburden hummocks have the highest diversity (s) and highest Shannon diversity
(Table 5.1). The evenness (J') is among the highest as well indicating even distribution
among species. The age of the hummocks may be the reason more species and higher
diversity were recorded. More stable conditions reached during equilibrium may promote
the growth of more species. Climatic conditions, soil composition, nutrient availability
may all influence the diversity as well. While the Agrifos overburden hummocks have
similar high values for diversity, the Cargill overburden hummocks show much lower
diversities. This may be attributed to the late construction of the Cargill site. Different
5-49
species colonizing the hummocks during the latter part of the growing season may be the
cause of the discrepancy.
Another possible reason for the difference comes to light when looking at the
percent cover. The overburden hummocks in the Cargill wetland have much higher
percent cover than do the Agrifos overburden hummocks. Combining the fact that
vegetation is abundant with the low diversities shows that a few select species are
dominating. This fact may also be attributed to the late construction of the hummocks.
The organic hummocks in both the Agrifos and Cargill wetlands show higher percent
cover when compared to the overburden hummocks. As stated previously, they may have
higher nutrient availability and have higher soil moisture than the overburden hummocks,
which is the likely cause of more vegetation cover. The values for diversity are similar
for the organic hummocks in both wetlands. Similar soil conditions and nutrient
availability likely exist for hummocks in both wetlands.
Tree survivorship and growth from the wetlands can not be compared because of
the lack of early stage data. Only initial data were available from the Cargill site, and no
early numbers were available from Iluka site.
VALUE OF HUMMOCKS IN WETLANDS
The advantage of hummocks can be seen from the data shown in Table 5.2.
Diversity indices are higher on the hummocks than off in all cases. The variation in
micro-site hydrology found on the hummocks permits a wide variety of plants with
different ranges of moisture requirements to establish themselves. The relatively uniform
moisture found in the flat areas off the hummocks only allows growth of plants tolerant
to high soil moisture and/or flooded conditions. These results substantiate those found by
Sloan (1998) and Bukata (1999) in previous microtopography studies. Sloan found that
species diversity increased with increased hummock frequency (rugosity) and expanded
elevation ranges in lake and stream systems. Bukata found that constructed hummocks
significantly contribute to the overall species richness and diversity of a constructed
wetland. Species richness and diversity was higher on hummocks than areas between
hummocks.
Evenness numbers are higher off the hummocks in situations where there is a low
number of species. The Agrifos wetland has a high number of species living off the
hummocks and lower evenness than on the hummocks. The other two wetlands have
higher evenness off the hummocks and have fewer species growing off the hummocks.
The numbers are not dramatically different and might not indicate anything significant.
The soil moisture off the hummocks in the Iluka wetland and the water level in the
Cargill wetland were higher in relation to the hummocks than in the Agrifos. That fact
might explain why fewer species were growing off the hummocks and why they are
slightly more evenly distributed. Fewer plants were tolerant of the higher moisture
conditions in the Iluka and Cargill wetlands. Those that were tolerant had an even
distribution. In the Agrifos wetland, conditions were tolerated by more species, but some
species flourished where others did not.
5-50
The flooded conditions also likely explain the lower percent cover found off the
hummocks in the Cargill wetland than in the other two wetlands. The trend can be seen in
the Iluka wetland as well. Later in the growing season, when standing water began to
accumulate, the percent cover off the hummocks in the Iluka wetland began to decrease.
High soil moisture conditions similar to those found early in the growing season in the
Iluka wetland are conducive to a high volume of vegetation growth. The trend can be
seen in the Agrifos wetland. Early in the growing season, when the wetland was dry,
there is little vegetation cover. As the wetland began to fill with water and the soil
became moister, the percent cover went up. The Agrifos wetland never experienced
flooded conditions as seen in the Cargill and Iluka wetlands, so the downward trend was
never seen. The moist conditions allow rapid uptake of nutrients for those plants tolerant
of the high moisture conditions, which leads to higher growth. Lower percent cover was
seen on the hummocks than off the hummocks in all situations when flooded conditions
did not exist. This lends further credence to the idea that the high moisture conditions
lead to more plant growth. The lower moisture conditions found at the top of the
hummocks during non-flood stage do allow growth different species than in the high
moisture conditions, but do not allow as much growth due to lower nutrient uptake.
The community similarity (Table 5.3) shows that the plants growing on the
hummocks are different than those growing off the hummocks. The difference in water
regime between the two communities confines most plants to one of the two community
types. Some plants tolerant of a wide range of moisture conditions are found on the
hummocks and off the hummocks as indicated by the Sorensen coefficient.
Increased tree growth is the other supposed advantage of hummocks. Bukata
(1999) noted that hummocks appear to provide sites, which allow for increased
survivorship and growth of wetland tree stock. Table 5.4 shows that cypress trees planted
on the hummocks in the Iluka wetland have grown more than those planted off the
hummocks. This is likely because when a tree is stressed, as it would be in flooded
conditions, more energy goes to overcoming the stressed condition than goes to growth.
On the hummock, where soil conditions are drier, the tree can put more energy towards
growth than maintenance. Unfortunately, little can be said about the trees in the Agrifos
wetland. Initial data on the numbers and sizes of trees planted off the hummocks were
unattainable because of the planting conditions. Data for survivorship, as seen for on
hummock conditions, can not be calculated. Little can be said about growth at this time
either. The relatively slow growth of trees makes one growing season of data hard to
decipher. The trees on the hummocks look like they grew taller than the trees off the
hummocks, and those off the hummocks look to be shorter with wider trunks. Water
regime might account for the difference, but without initial planting data, that can not be
stated as fact.
5-51
CONCLUSIONS
While no definitive conclusions about either the value of hummocks or the best
material from which to construct them can be drawn from this project, a few
recommendations can be made based on the features the hummocks are lacking. The
composted organic material used in the Agrifos wetland showed 2% more change in
cross sectional area than the overburden hummocks and 4% more than the sand
hummocks. The composted organic material did not provide for tree survivorship as only
17% of the pop ash and 33% of the sweet bay survived the first growing season. Sand
tailings appear to be a reasonable choice because it has high diversity, 100% ash and 83%
bay tree survivorship, and only 2% change in cross sectional area. Two functional flaws
exist with sand tailings: it holds little pore water and has only 23% understory cover.
Overburden had no fatal flaws and performed well in both the Cargill and Agrifos
wetlands. The overburden hummocks had 100% tree survivorship in the Agrifos wetland,
over 30% understory vegetation cover, high species diversity, and only 2% (Cargill) and
4% (Agrifos) change in cross sectional area during the first growing season. The organic
hummocks in the Cargill wetland also performed to a high standard and may prove to be
the most desirable by long term study. Muck does have one drawback when compared to
overburden in that it must be hauled into the site for construction. Overburden is already
on site and thus costs less than muck. Those cost differences must be weighed against the
performance of the hummock types. Continued data collection over multiple growing
seasons would provide more definite information on the performance of these materials,
especially tree survivorship and growth and long term stability of the hummocks. The
data collected during this study show a definite advantage in using hummocks in order to
increase species diversity, especially in situations where the wetlands will be flooded for
the majority of the growing season. Further study will show if the superior tree growth
seen in the Iluka wetland applies to more than cypress trees. Survivorship will also be
better understood after the trees in the Cargill and Agrifos wetlands are monitored over
multiple growing seasons. Based on this study and those of Sloan (1998) and Bukata
(1999), hummocks do appear to be beneficial to the overall structure and health of a
wetland and should be included in new construction.
5-53
REFERENCES
Brower JE, Zar JH, von Ende CN. 1990. Field and laboratory methods for general
ecology. Dubuque (IA): W. C. Brown Publishers.
Bukata BJ. 1999. The development and role of microtopography in constructed forested
wetlands on phosphate mined lands in central Florida [MS thesis]. Gainesville (FL):
University of Florida.
Chapra SC, Canale RP. 1988. Numerical methods for engineers. 2nd ed. New York:
McGraw-Hill, Inc.
Conner WH, Gosselink JG, Parrondo RT. 1981. Comparison of the vegetation of three
Louisiana swamp sites with different flooding regimes. Am. J. Bot. 68(3):320-31.
Crampton CB. 1977. A study of the dynamics of hummocky microrelief in the Canadian
north. Can. J. Earth Sci. 14:639-49.
Hardin ED, Wistendahl WA. 1983. The effects of floodplain trees on herbaceous
vegetation patterns, microtopography, and litter. J. Torrey Bot. Soc. 110(1):23-30.
Hmieleski JI. 1994. High marsh-forest transitions in a brackish marsh: the effects of
slope [MS thesis]. Greenville (NC): East Carolina University.
Hosner JF. 1960. Relative tolerance to complete inundation of fourteen bottomland tree
species. For. Sci. 6(3):246-51.
Huenneke LF, Sharitz RR. 1986. Microsite abundance and distribution of woody
seedlings in a South Carolina cypress-tupelo swamp. Am. Midl. Nat. 115(2):328-35.
Kozlowski TT. 1979. Tree growth and environmental stresses. Seattle (WA): University
of Washington Press.
Lowry DJ. 1989. Restoration and creation of palustrine wetlands associated with riverine
systems of the glaciated northeast. In: Kunsler JA, Kentula ME, editors. Wetland
creation and restoration: the status of the science, Vol. I. Washington: U.S.
Environmental Protection Agency. Publication nr 600/3-89/038a.
Mackay JR. 1980. The origin of hummocks, western Arctic coast, Canada. Can. J. Earth
Sci. 17:996-1006.
Munro M, Shaw J. 1997. Erosional origin of hummocky terrain in south-central Alberta,
Canada. Geology 25(11):1027-30.
5-55
Sloan M. 1998. The role of microtopographic relief in maintaining understory vegetative
community diversity in forested wetlands [MS thesis]. Gainesville (FL): University of
Florida.
South Carolina Department of Natural Resources and U.S. Department of Commerce,
National Oceanic and Atmospheric Administration Coastal Services Center and National
Geophysical Data Center. 1996. Ecological characterization of Otter Island, South
Carolina: a prototype for interactive access to coastal management information.
Charleston (SC): U.S. Department of Commerce, National Oceanic and Atmospheric
Administration, Coastal Services Center. Publication nr NOAA CSC/7-96/001.
Odum HT, Odum EC, Brown MT. 1998. Environment and society in Florida. Boca
Raton (FL): St. Lucie Press.
Reddy KR, Patrick WH Jr. 1983. Effects of aeration on reactivity and mobility of soil
constituents. In: Chemical mobility and reactivity in soil systems: proceedings of a
symposium; 1981 29 Nov-3 Dec; Atlanta, GA. Madison (WI): Soil Science Society of
America. Special Publication nr 11.
Sharma PP, Gupta SC, Foster GR. 1993. Predicting soil detachment by raindrops. Soil
Sci. Soc. Am. J. 57:674-80.
Theta Meter: hand-held readout unit for ThetaProbe. User manual. 1997. Burwell,
Cambridge, UK: Delta-T Devices Ltd.
ThetaProbe: soils moisture sensor user manual. 1998. Burwell, Cambridge, UK: Delta-
T Devices Ltd.
Thomas BP, Cummings E, Wittstruck WH. 1985. Soil survey of Alachua County,
Florida. Washington: United States Department of Agriculture, Soil Conservation
Service.
Titus JH. 1990. Microtopography and woody plant regeneration in a hardwood floodplain
swamp in Florida. J. Torrey Bot. Soc. 117(4):429-37.
Vivian-Smith G. 1997. Microtopographic heterogeneity and floristic diversity in
experimental wetland communities. J. Ecol. 85:71-82.
5-56
APPENDIX 5-A
ELEVATION ALONG MAJOR AND MINOR TRANSECTS
99
98.8
98.6
98.4
98.2
98
97.8
97.6
97.4
97.2
97
0 2 4 6 8 10 12 14
Major Transect Length (ft)
98.5
97.5
0 2
- Elev. 4/3
- --Elev. 8/5
4 6
Minor Transect Length
- Elev. 4/23
----Elev. 10/13
------ Elev. 5/19
- Elev. Sum/2000
Figure 5A-1. Elevation Along Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 1.
5A-1
100
99.5
" 99
S98.5
98
97.5
97
2 4 6 8
Major Transect Length (ft)
99.5
99
| 98.5
. 98
97.5
10 12 14
0 2 4 6 8
Minor Transect Length (ft)
-- Elev. 4/3 Elev. 4/23 Elev. 5/19
- Elev. 8/5 -- Elev. 10/13 Elev. Sum/2000
Figure 5A-2. Elevation Along Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 2.
5A-2
100.5
100
99.5
99
" 98.5
98
97.5
97
0 2 4 6 8
Major Transect Length (ft)
100.5
100
99.5
99
98.5
98
97.5
97
10 12 14
0 2 4 6 8
Minor Transect Length (ft)
-- Elev. 4/3 Elev. 4/23 Elev. 5/19
----- Elev. 8/5 - Elev. 10/13 Elev. Sum 2000
Elevation Along.Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 3.
5A-3
Figure 5A-3.
99.4 (a)
99.2
99
98.8 -
98.6 -
98.4
98.2 -
98 -
97.8 -
97.6
97.4
97.2 -
0 2 4 6 8 10 12 14
Major Transect Length (ft)
0 2 4 6 8 10
Minor Transect Length (ft)
Elev. 4/3
----Elev. 8/5
- -Elev. 4/23
- Elev. 10/13
Elev. 5/19
Elev. Sum 2000
Figure 5A-4. Elevation Along Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 4.
5A-4
99.2
99
98.8
- 98.6
98.4
I 98.2
98
S97.8
97.6
97.4
97.2
100
99.5
99
98.5
98
97.5
97
0 2 4 6 8 10 12 14
Major Transect Length (ft)
0 1 2 3 4 5 6 7 8
Minor Transect Length (ft)
Elev. 4/3
----Elev. 8/5
- "Elev. 4/23
- Elev. 10/13
Elev. 5/19
Elev. Sum 2000
Figure 5A-5. Elevation Along Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 5.
5A-5
99.6
99.4
99.2
S99
98.8
, 98.6
.0 98.4
> 98.2
98
97.8
97.6
97.4
100
99.5
99
98.5
98
97.5
97
0 2 4 6 8 10 12 14
Major Transect Length (ft)
100 (b)
99.5
2 99
= 98.5
G 98
97.5
97 ..
0 2 4 6 8 10
Minor Transect Length (ft)
Elev. 4/3 -Elev. 4/23 Elev. 5/19
-. Elev. 8/5 Elev. 10/13 Elev. Sum 2000
Figure 5A-6. Elevation Along Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 6.
5A-6
99
98.8
98.6
S98.4
c 98.2
0
> 98
97.8
97.6
97.4
0 2 4 6 8
Major Transect Length (ft)
10 12 14
99 1
(b)
98.8
98.6 /
S98.4
g 98.2
o
S98
97.8
97.6
97.4
0 2 4 6 8 10
Minor Transect Length (ft)
Elev. 4/3 "Elev. 4/23 Elev. 5/19
Elev. 8/5 Elev. 10/13 Elev. Sum 2000
Figure 5A-7. Elevation Along Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 7.
5A-7
99.5
99
98.5
98
97.5
97
0 2 4 6 8 10 12 14
Major Transect Length (ft)
99.4
99.2
99
98.8
98.6
98.4
98.2
98
97.8
97.6
97.4
1 2 3 4 5 6 7
Minor Transect Length (ft)
Elev. 4/3
----Elev. 8/5
- "Elev. 4/23
- Elev. 10/13
Elev. 5/19
Elev. Sum 2000
Figure 5A-8. Elevation Along Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 8.
5A-8
100
99.5
99
r98.5
o
S98
97.5
97
100
99.5
li^
99
0
S 98.5
98
97.5
0 2 4 6 8
Major Transect Length (ft)
10 12 14
0 2 4 6 8
Minor Transect Length (ft)
Elev. 4/3 -Elev. 4/23 Elev. 5/19
Elev. 8/5 Elev. 10/13 Elev. Sum 2000
Figure 5A-9. Elevation Along Major Transect (a) and Minor Transect (b) on
Agrifos Hummock 9.
5A-9
100
99.5
99
S98.5
o
98
97.5
97
99.5
99
2
C98.5
o
S98
0 2
Elev. 4/3
- Elev. 8/5
4 6 8
Minor Transect Length (ft)
- -Elev. 4/23 Elev. 5/19
- Elev. 10/13 Elev. Sum 2000
Figure 5A-10. Elevation Along Major Transect (a) and Minor Transect (b)
on Agrifos Hummock 10.
5A-10
0 2 4 6 8 10 12 14
Major Transect Length (ft)
97.5
97
100
99.5
99
c98.5
98
S98
Mj
97.5
97
0 2 4 6 8 10
Major Transect Length (ft)
(b)
99.6
99.4
99.2
99
98.8
98.6
98.4
98.2
98
97.8
97.6
97.4
0 1 2 3 4 5 6 7
Minor Transect Length (ft)
Elev. 4/3
- Elev. 8/5
- "Elev. 4/23
- Elev. 10/13
Elev. 5/19
--"Elev. Sum 2000
Figure 5A-11. Elevation Along Major Transect (a) and Minor Transect (b)
on Agrifos Hummock 11.
5A-11
100
99.5
99
z98.5
0o
; 98
97.5
97
2 4 6
8 10 12 14
Major Transect Length (ft)
100
99.5
C 99
o
S98.5
98
97.5
2 4 6 8
Minor Transect Length (ft)
Elev. 4/3
- --Elev. 8/5
- "Elev. 4/23
- Elev. 10/13
Elev. 5/19
Elev. Sum 2000
Figure 5A-12. Elevation Along Major Transect (a) and Minor Transect (b)
on Agrifos Hummock 12.
5A-12
98.6
98.4
98.2
C/)
98
" 97.8
m 97.6
97.4
97.2
0 2 4 6 8 10 12 14
Major Transect Length (ft)
98.6 (b)
(b)
98.4
8.2
98 -
97.8
97.6
97.4 24 5
0 1 2 3 4 5 6 7 8
Elev. 4/3
----Elev. 8/5
- "Elev. 4/23
Elev. Sum 2000
Figure 5A-13. Elevation Along Major Transect (a) and Minor Transect (b)
on Agrifos Hummock 13.
5A-13
Elev. 5/19
99.5
99
c 98.5
g 98
S97.5
97
96.5
2 4 6 8 10
Major Transect Length (ft)
99
98.5
5 98
197.5
97
96.5 -...
0 1 2 3 4 5 6 7 8
Elev. 4/3
- Elev. 8/5
- -"Elev. 4/23
Elev. Sum 2000
Figure 5A-14. Elevation Along Major Transect (a) and Minor Transect (b)
on Agrifos Hummock 14.
5A-14
-- Elev. 5/19
99.5
99
CIO
598.5
o
98
97.5
97
99.5
99
S98.5
0
f98
M
97.5
97
0 2 4 6 8 10 12 14
Major Transect Length (ft)
0 2 4 6 8
Minor Transect Length (ft)
Elev. 4/3 -"Elev. 4/23 Elev. 5/19
Elev. 8/5 Elev. 10/13 Elev. Sum 2000
Figure 5A-15. Elevation Along Major Transect (a) and Minor Transect (b)
on Agrifos Hummock 15.
5A-15
98.8
98.6
98.4
C 98.2
g 98
97.8
97.6
97.4
97.2
0 2 4 6 8 10 12 14
Major Transect Length (ft)
98.8
98.6
98.4
v98.2
= 98
o
>97.8
97.6
97.4
97.2
2 4 6 8
Minor Transect Length (ft)
Elev. 4/3
- Elev. 8/5
- -Elev.4/23
- Elev. 10/13
Elev. 5/19
Elev. Sum 2000
Figure 5A-16. Elevation Along Major Transect (a) and Minor Transect (b)
on Agrifos Hummock 16.
5A-16
|
