ANNUAL REPORT FOR 2003
Little Sugar Creek Mitigation Site
Mecklenburg County
Project No. 8.U670122
TIP No. R-211 DA
Office of Natural Environment & Roadside Environmental Unit
North Carolina Department of Transportation
December 2003
TABLE OF CONTENTS
SUMMARY...................................................................................................................... 1
1.0 INTRODUCTION.................................................................................................. 2
1.1 PROJECT DESCRIPTION......................................................................... 2
1.2 PURPOSE ................................................................................................. 2
1.3 PROJECT HISTORY ................................................................................. 4
1.4 DEBIT LEDGER ........................................................................................ 4
2.0 HYDROLOGY ...................................................................................................... 5
2.1 SUCCESS CRITERIA................................................................................ 5
2.2 HYDROLOGIC DESCRIPTION ................................................................. 5
2.3 RESULTS OF HYDROLOGIC MONITORING........................................... 7
2.3.1 Site Data ......................................................................................... 7
2.3.2 Climatic Data................................................................................. 10
2.4 CONCLUSIONS ...................................................................................... 10
3.0 VEGETATION: LITTLE SUGAR CREEK MITIGATION SITE........................... 12
3.1 SUCCESS CRITERIA.............................................................................. 12
3.2 DESCRIPTION OF SPECIES.................................................................. 12
3.3 RESULTS OF VEGETATION MONITORING.......................................... 13
3.4 CONCLUSIONS ...................................................................................... 13
4.0 OVERALL CONCLUSIONS/RECOMMENDATIONS......................................... 14
LIST OF FIGURES
Figure 1. Site Location Map...................................................................................... 3
Figure 2. Gauge Location and Site Modification Map ............................................... 6
Figure 3. 2003 Hydrologic Monitoring Results .......................................................... 9
Figure 4. Little Sugar Creek 30-70 Graph, Charlotte, NC ....................................... 11
LIST OF TABLES
Table 1. Little Sugar Creek Mitigation Site Debit Ledger ......................................... 4
Table 2. 2003 Hydrologic Monitoring Results .......................................................... 8
Table 3. Vegetation Monitoring Statistics............................................................... 13
APPENDICES
APPENDIX A GAUGE DATA GRAPHS
APPENDIX B SITE PHOTOS/PHOTO AND PLOT LOCATIONS
APPENDIX C LETTER TO N.C. WETLAND RESTORATION PROGRAM,
OCTOBER 8, 2001
APPENDIX D LETTER TO U.S DEPARTMENT OF THE ARMY,
AUGUST 29, 2003
APPENDIX E MITIGATION SITE SOIL ANALYSIS
SUMMARY
The Little Sugar Creek Mitigation Site, located in Mecklenburg County, is in its seventh
year of monitoring. Approximately 21 acres in size, the site was to serve as mitigation
for the R-211DA section of the Charlotte Outer Loop. It was constructed in the winter of
1996-97. The site must demonstrate hydrologic and vegetation success for a minimum
of three years or until the site is deemed successful.
The daily rainfall data depicted on the gauge data graphs was recorded from an onsite
rain gauge that was installed on May 4, 2000. Additional Charlotte rainfall data used for
the 30-70 graph was provided by the NC State Climate Office. The onsite rain gauge
experienced periodic malfunctions; therefore rainfall data from the Charlotte weather
station was used for the gauge graphs. In 2003, Charlotte experienced a wet growing
season, resulting in an average to above average rainfall year.
In August 2003, NCDOT provided a letter to the U.S. Department of the Army to
address the hydrologic concerns of securing an additional 13.1 acres of wetlands to
replace the Little Sugar Creek Mitigation Site (Appendix D). NCDOT is currently in
discussion regarding this issue.
In October 2003, The Catena Group, Inc. conducted a site visit to evaluate the Little
Sugar Creek Mitigation Site. The investigation examined soil features to determine any
correlation between the past and current conditions on the site. The report can be
found in Appendix E. Mitigation Site Soil Analysis.
During the 2003-monitoring year, six of the nine gauges met the jurisdictional hydrology
(saturation for 12.5% of the growing season). Two of the nine gauges that did not meet
success experienced malfunctions, early in the growing season. The surface water
gauges indicated persistent surface water in the channels throughout the growing
season.
The emergency spillway modifications improved the site, hydraulically in the 2003-
monitoring year. During an average to above average rainfall year, eight of the nine-groundwater
gauges improved from the 2002-monitoring year (below average rainfall
year).
Vegetation survival rates at the site are above the minimum success criteria. The
average density for bottomland hardwood species was 408 trees per acre after seven
years. Planted shrub species were observed at a density of 317 stems per acre.
NCDOT proposes to discontinue vegetation monitoring at the Little Sugar Creek
Mitigation Site.
NCDOT will continue to monitor the site for hydrology.
1
1.0 INTRODUCTION
1.1 PROJECT DESCRIPTION
The Little Sugar Creek Mitigation Site is located in Mecklenburg County. The site,
which encompasses approximately 21 acres, is situated at the intersection of Highway
51 and Leitner Drive (Figure 1). It was designed as mitigation for a portion of the
Charlotte Outer Loop project that extends from NC 51 to Rea Road (TIP No. R-211 DA,
USACE Action ID 199200013).
The project provides for the restoration/creation of bottomland forest, shrub-scrub
wetland, and emergent marsh. The site was originally constructed in the winter 1996-
97; NCDOT performed supplemental planting work in 1998. The site is in its second
year of hydrologic and vegetation monitoring following the site modification prior to the
2002 growing season.
1.2 PURPOSE
In order to demonstrate successful mitigation, Little Sugar Creek is monitored for both
hydrology and vegetation. The following report describes the results of the hydrologic
and vegetative monitoring during 2003 at the Little Sugar Creek Mitigation Site.
Included in this report are the hydrologic and vegetation monitoring results, as well as
an analysis of local climate conditions throughout the growing season, and site
photographs.
2
Figure 1. Site Location Map
Carolina
Place Mall
Little Sugar Creek
Wetland Mitigation Site
3
1.3 PROJECT HISTORY
March 1997 Site Planted
March-November 1997 Hydrologic Monitoring (1 yr.)
September 1997 Vegetation Monitoring (1 yr.)
March 1998 Shrub Area Replanted
March-November 1998 Hydrologic Monitoring (2 yr.)
September 1998 Vegetation Monitoring (2 yr.)
March-November 1999 Hydrologic Monitoring (3 yr.)
September 1999 Vegetation Monitoring (3 yr.)
March-November 2000 Hydrologic Monitoring (4 yr.)
September 2000 Vegetation Monitoring (4 yr.)
February 2001 Raised Weir at Sheet Piles
March-November 2001 Hydrologic Monitoring (5 yr.)
June 2001 Vegetation Monitoring (5 yr.)
March 2002 Adjusted Emergency Spillway
Elevations
March-November 2002 Hydrologic Monitoring (6 yr.)
August 2002 Vegetation Monitoring (6 yr.)
March-November 2003 Hydrologic Monitoring (7 yr.)
September 2003 Vegetation Monitoring (7 yr.)
October 2003 Soils Investigation
1.4 DEBIT LEDGER
Table 1. Little Sugar Creek Mitigation Site Debit Ledger
Mitigation Plan TIP Debit
Site Habitat Wetland Acres
At Start
Acres Remaining % Remaining R-211DA
BLH, Scrub
Shrub, FWM 16.1 0 0.0 16.1
BLH: Bottomland Hardwood FWM: Freshwater Marsh
4
2.0 HYDROLOGY
2.1 SUCCESS CRITERIA
In accordance with federal guidelines for wetland mitigation, the success criteria for
hydrology state that areas must be inundated or saturated (within 12 inches of the
surface) by surface or groundwater for at least a consecutive 12.5% of the growing
season. Areas inundated for less than 5% of the growing season are always classified
as non-wetlands. Areas inundated between 5% and 12.5% of the growing season can
be classified as wetlands depending upon such factors as the presence of wetland
vegetation and hydric soils.
The growing season in Mecklenburg County begins March 22 and ends November 11
(235 days). These dates correspond to a 50% probability that air temperatures will not
drop below 28ºF or lower after March 22 and before November 11.1 Minimum wetland
hydrology is required for at least 12.5% of this growing season; for Mecklenburg
County, this 12.5% equals 29 consecutive days. Local climate must represent average
conditions for the area in order for the hydrologic data to be considered successful.
2.2 HYDROLOGIC DESCRIPTION
Nine groundwater gauges, one rain gauge, and three 80-inch surface water gauges
were installed in 1997 (Figure 2). The automatic monitoring gauges record daily
readings of the groundwater depth.
The sluice gates, which were closed in July 1999 to hold surface water on the site,
remained closed in 2003. In an attempt to further augment the site hydrology, the weir
was raised approximately eight inches in the ditch where the sheet piles are located and
clay was added to the face of the rip-rap at the emergency spillway in 2001. The
elevation of both emergency spillway outlets was raised to match the elevation of the
flood control structure in March 2002.
Runoff from the surrounding area is the primary hydrologic input to the Little Sugar
Creek Site. A stormwater pipe, running underneath Leitner Drive, releases water
collected from adjacent shopping centers near Gauge 9. The monitoring gauges on the
site show the effects of the stormwater collected in the channels, as well as the effects
of specific rainfall events on the groundwater table.
1 Natural Resources Conservation Service, Soil Survey of Mecklenburg County, North Carolina, p.61.
5
Figure 2. Gauge Location and Site Modification Map
6
2.3 RESULTS OF HYDROLOGIC MONITORING
2.3.1 Site Data
To determine if the site met the federal guidelines (saturation within 12 inches of the
surface for at least 12.5% of the growing season), the maximum number of consecutive
days that the groundwater was within twelve inches of the surface was determined for
each gauge. This number was converted into a percentage of the 235-day growing
season. The results are presented in Table 2.
Appendix A contains a plot of the groundwater and surface water depth for each
groundwater and surface gauge, respectively. The individual precipitation events,
shown on the monitoring gauge graphs as bars, represent data collected from the on-site
rain gauge or from a Charlotte weather station (provided by the NC State Climate
Office). The maximum number of consecutive days is noted on each graph. The rain
gauge on the site was replaced with a more accurate measuring device prior to the
2000-monitoring season.
The placement of the groundwater gauges and a graphical representation of the
hydrologic monitoring results are provided in Figure 3.
7
Table 2. 2003 Hydrologic Monitoring Results
Monitoring
Gauge < 5% 5-8% 8-12.5% > 12.5% Actual
%
Dates of
Success
LSC-2 r 39.6
April 17-July 18
July 30-Aug 28
LSC-4 r 0.9
LSC-5 r 10.6 Aug 4-Aug 28
LSC-6 r 41.7 March 22-June 27
LSC-7 r 40.9 March 22-June 25
LSC-8 r 14.0 July 30-August 31
LSC-9 r 19.1
June 7-July 21
July 30-August 30
LSC-11 r 7.7
LSC-12 r 17.0 March 22-April 30
The 2003 growing season experienced an above average rainfall year.
Specific gauge problems:
• Gauge 4 did not record data from January to July 17 or August 26 to November 13
due to battery failure and gauge replacement.
• Gauges 2, 5, 8, 9 were not downloaded during the beginning of the growing season
due to the depth of inundation around the gauges.
• Gauge 5 had a battery failure June 7 to July 17.
8
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2.3.2 Climatic Data
Figure 4 is a comparison of 2002 and 2003 monthly rainfall to historical precipitation for
the area. This comparison indicates if 2003 was “average” in terms of climate
conditions by comparing the rainfall to that of historical rainfall (data collected between
1972 and 2003). The NC State Climate Office provided all historical data.
For the 2003-year, November (02’), December (02’), March, April, May, June, July, and
August experienced above average rainfall. The months of January, October, and
November recorded below average rainfall for the site. February and September
experienced average rainfall. Overall, 2003 experienced an average to above average
rainfall year.
2.4 CONCLUSIONS
During the 2003-monitoring year, six of the nine gauges met the jurisdictional hydrology
(saturation for 12.5% of the growing season). Two of the nine gauges that did not meet
success experienced malfunctions, early in the growing season. The surface water
gauges indicated persistent surface water in the channels throughout the growing
season.
The emergency spillway modifications improved the site, hydraulically in the 2003-
monitoring year. During an average to above average rainfall year, eight of the nine-groundwater
gauges improved from the 2002-monitoring year (below average rainfall
year).
NCDOT will continue to monitor the Little Sugar Creek Mitigation Site for hydrology.
10
Figure 4. 30-70 Percentile Graph
Little Sugar Creek 30-70 Percentile Graph
Charlotte, NC
0
2
4
6
8
10
12
Nov 02' Dec 02' Jan 03' Feb 03' Mar 03' Apr 03' May 03' Jun 03' Jul 03' Aug 03' Sep 03' Oct 03' Nov 03' Dec 03'
Date
Precipitation (in.)
2002 Rainfall 2032 Rainfall 30th Percentile 70th Percentile
30th Percentile
70th Percentile
11
3.0 VEGETATION: LITTLE SUGAR CREEK MITIGATION SITE
(YEAR 7 MONITORING)
3.1 SUCCESS CRITERIA
Success criteria state that there must be a minimum mean density of 320 characteristic
tree species/acre surviving for at least three years in the bottomland forest area of the
site. Characteristic tree species are those species planted along with natural
recruitment of sweetgum, red maple, and loblolly pine. Loblolly pine cannot comprise
more than 10% of the 320 trees per acre. No quantitative sampling requirements were
developed for the herbaceous and shrub assemblages as part of the vegetation
success criteria per the August 1995 mitigation plan.
3.2 DESCRIPTION OF SPECIES
The following shrub species were re-planted in the Wetland Shrub Restoration Area:
Cornus amomum, Silky Dogwood
Leucothoe axillaris, Dog Hobble
Rhododendron arborescens, Smooth Azalea
Sambucus canadensis, Elderberry
Viburnum nudum, Possum Haw
Aesculus sylvatica, Painted Buckeye
Lindera benzoin, Spicebush
The following herbaceous species were planted in the Channel Areas:
Juncus effusus, Soft Rush
Scirpus validus, Bulrush
The following tree species were planted in the Wetland Restoration Area:
Quercus michauxii, Swamp Chestnut Oak
Quercus falcata var. pagodaefolia, Cherrybark Oak
Quercus phellos, Willow Oak
Fraxinus pennsylvanica, Green Ash
Betula nigra, River Birch
Quercus lyrata, Overcup Oak
Quercus nigra, Water Oak
12
3.3 RESULTS OF VEGETATION MONITORING
Table 3. Vegetation Monitoring Statistics
Plot # (Type)
Silky Dogwood
Dog Hobble
Painted Buckeye
Green Ash
Water Oak
Cherrybark Oak
Overcup Oak
Swp Chestnut Oak
River Birch
Willow Oak
Total (7 year)
Total (at planting)
Density (Trees/Acre)
1 (
2 (
3 (
Shrub) 14 14 30 317
BLH) 13 2 2 3 20 30 453
BLH) 10 1 1 1 3 16 30 363
AVERAGE TREE (BLH) D ENSITY 408
Site Notes: Other species noted: Juncus sp., Queen-Anne’s-lace, various grasses,
foxtail, switchgrass, fennel, sycamore, locust, smartweed, volunteer green ash and
gum, milkweed, Aster sp., wooly panicum, ragweed, woolgrass, and cottonwood.
Elderberry noted in plot 1. Silky dogwood was noted in plots 2 and 3. Ditches were full
of Juncus sp. Beaver activity was noted in plots 2 and 3.
3.4 CONCLUSIONS
Approximately 9.8 acres of this site were planted in bottomland hardwoods in March
1997. There were two vegetation monitoring plots established in the bottomland
hardwood area, Plots #2 and #3. The 2003 vegetation monitoring revealed an average
density of 408 trees per acre, which is above the 320 trees/acre minimum requirement.
Approximately 3.2 acres of this site were planted with shrub species. The 2003
vegetation monitoring of Plot #1 revealed an average density of 317 stems per acre.
The remaining 3.7 acres were planted with herbaceous plant material. From visual
observation, this plant material has established in the bottom and on the side slopes of
the channels on the site.
NCDOT proposes to discontinue vegetation monitoring at the Little Sugar Creek
Mitigation Site.
13
4.0 OVERALL CONCLUSIONS/RECOMMENDATIONS
In August 2003, NCDOT provided a letter to the U.S. Department of the Army to
address the hydrologic concerns of securing an additional 13.1 acres of wetlands to
replace the Little Sugar Creek Mitigation Site (Appendix D). NCDOT is currently still in
discussion regarding this issue.
In October 2003, The Catena Group, Inc. conducted a site visit to evaluate the Little
Sugar Creek Mitigation Site. The investigation examined soil features to determine any
correlation between the past and current conditions on the site. The report can be
found in Appendix D. Mitigation Site Soil Analysis.
During the 2003-monitoring year, six of the nine gauges met the jurisdictional hydrology
(saturation for 12.5% of the growing season). Two of the nine gauges that did not meet
success experienced malfunctions, early in the growing season. The surface water
gauges indicated persistent surface water in the channels throughout the growing
season.
Vegetation survival rates at the site are above the minimum success criteria. The
average density for bottomland hardwood species was 408 trees per acre after seven
years. Planted shrub species were observed at a density of 317 stems per acre.
NCDOT proposes to discontinue vegetation monitoring at the Little Sugar Creek
Mitigation Site.
NCDOT will continue to monitor the site for hydrology.
14
APPENDIX A
GAUGE DATA GRAPHS
APPENDIX B
SITE PHOTOS
PHOTO/PLOT LOCATIONS
Little Sugar Creek
Photo 1 Photo 2
Photo 3 Photo 4
Photo 5 Photo 6
2003
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
APPENDIX C
LETTER TO N.C. WETLAND RESTORATION PROGRAM,
OCTOBER 8, 2001
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
APPENDIX D
LETTER TO U.S DEPARTMENT OF THE ARMY,
AUGUST 29, 2003
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
APPENDIX E
MITIGATION SITE SOIL ANALYSIS
INTRODUCTION
The Little Sugar Creek Mitigation Site and Mallard Creek Mitigation Site are the property
of the North Carolina Department of Transportation (NCDOT). Both sites are located in
Mecklenburg County, NC and have been constructed to provide wetland mitigation for
NCDOT road projects in the county.
Little Sugar Creek was constructed in the winter of 1996-97. The site was modified in
2002 in an effort to increase its hydrologic regime. Mallard Creek was constructed in
1994 and underwent remediation in 1997. It is divided into two sites. Site 1 is located
south of Mallard Creek Church Road. Site 2 is located on the opposite side of Mallard
Creek Church Road.
The hydrologic success as stated in the both Mitigation Plans reads:
“…that the area must be inundated or saturated (within 12” of the surface) by
surface or groundwater for at least a consecutive day percentage of 12.5% of the
growing season. Areas inundated or saturated for less than 5% of the growing
season are always classified as non-wetlands. Areas inundated or saturated
between 5% - 12.5% of the growing season can be classified as wetlands
depending on upon factors such as the presence of the wetland vegetation and
hydric soils.”
Aside from Mallard Creek Site 1, which has met the hydrologic success criteria for five
consecutive years, neither Little Sugar Creek nor Mallard Creek Site 2 have yet to fully
meet the hydrologic success criteria, despite efforts to modify both sites. As a result,
the US Army Corps of Engineers has requested that NCDOT determine the area of
each site that has failed to meet the hydrologic success criteria. Furthermore, they
have requested that NCDOT immediately provide alternative mitigation for the failed
section of the Little Sugar Creek Site through in-lieu payments to the North Carolina
Wetlands Restoration Program (WRP).
However prior to abandoning the failed sections and relinquishing the associated
mitigation credits, NCDOT has chosen to do additional research on the sites. It is
anticipated that this research will determine if the sites exhibit any characteristics that
suggest those failed sections could potentially meet the success hydrologic success
criteria. To this end, NCDOT has requested The Catena Group, Inc. to investigate both
sites, concentrating on the soils perspective.
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
Purpose
The purpose of this report is to evaluate the Little Sugar Creek Mitigation Site and the
Mallard Creek Mitigation Site. The investigation will examine the physical and
morphological features of the soils, as well as physical features of each site, in order to
determine any correlation between the past and current conditions. Based on these
findings, an assessment of the future viability of each site will be performed.
Wetland Creation
Wetland creation has been defined as the conversion of a persistent upland or shallow-water
area into a wetland by human activity (Mitsch and Gosselink, 2000). Both of the
subject sites can be considered creation sites in that they involved removal and grading
of earth to create areas of sustained hydrology at or near the soil surface.
The hydrologic success criteria for both sites require saturation within 12-inches of the
soil surface for at least 12.5% of the growing season for five consecutive years. In
Mecklenburg County, the growing season begins March 22 and extends through
November 11 (235 days), which equates to 29 consecutive days. If alterations are
made to the site, then the five-year monitoring periods must begin anew. While both
sites have been altered, they have been continually monitored since their creation.
Ecological Development of Created Wetlands
Understanding the complex nature of wetlands well enough to successfully create or
restore their function requires substantial training in plants, soils, wildlife, hydrology,
water quality, and engineering. According to Mitsch and Wilson (1996), a major flaw in
the measurement of wetland mitigation success is the limited amount of time that
regulators and the land development process allow for newly created wetlands to
develop before passing judgment. After five years of monitoring a mitigation wetland,
only a general idea of the wetlands ecological trajectory can be known. The further the
conditions are in the beginning from the targeted natural steady state, the longer it will
take for that system to reach or approach steady state. For example, the replacement
time frame for freshwater marshes is typically 15 or 20 years, far beyond the current
requirement of a 5 year establishment. Other wetland types such as forested wetlands,
coastal wetlands, or peatlands may take even longer (50 years to a lifetime) for wetland
functions to be restored (Mitsch and Gosselink, 2000).
Wetland soils
Wetland soils are both the medium in which many of the wetland chemical
transformations take place and are the primary storage of available nutrients for most
wetland plants. They are often described as hydric soils, defined by the U.S.
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
Department of Agriculture’s Natural Resources Conservation Service (NRCS) as “soils
that formed under conditions of saturation, flooding or ponding long enough during the
growing season to develop anaerobic conditions in the upper part”.
Wetland soils are of two types, mineral or organic. Nearly all soils have some organic
material, but when a soil has less than 20 to 35 percent organic matter (on a dry weight
basis), it is considered a mineral soil, as are the soils in both mitigation sites.
Wetland Soils Formation
When soils are inundated with water for an extended period, anaerobic conditions
usually result. The rate at which oxygen can diffuse through the soil is drastically
reduced, about 10,000 times slower than oxygen diffusion through a drained soil. This
low diffusion rate leads relatively quickly to anaerobic, or reduced conditions, with the
time required for oxygen depletion on the order of several hours to a few days after
inundation begins (Mitsch and Gosselink, 2000).
When a mineral soil is exposed to anaerobic conditions, it develops certain
characteristics that allow for its identification. These characteristics are collectively
called redoximorphic features, defined as features formed by the reduction,
translocation, and/or oxidation of iron (Fe) and manganese (Mn) oxides (Mitsch and
Gosselink, 2000). Soil inundation results in the development of these features, such as
a reduced matrix and redox concentrations (i.e., zones of apparent accumulation of Fe-
Mn oxides).
The development of redoximorphic features in mineral soils is mediated by micro-biological
processes. The rate at which they are formed depends on four conditions, all
of which must be present:
1. Saturated conditions
2. Sustained anaerobic conditions
3. Sufficient soil temperature (5° C is often considered “biological zero,” below
which much biological activity ceases or slows considerably)
4. Presence of organic matter to serve as a substrate for microbial activity
(Mitsch and Gosselink, 2000)
If microorganisms are not present, redoximorphic features will not form. If organic
carbon levels are too low, there may be insufficient microbial respiration to deplete the
diffused oxygen levels, even when the soil is saturated (Richardson and Vepraskas,
2001). Moving water tends to carry oxygen into the soil and retards the onset of Fe
reduction (Richardson and Vepraskas, 2001). The time required for Fe reduction to
occur after initiation of saturation or inundation depends on soil conditions. Studies
indicate that Fe reduction can take as little as one day to as long as four or more weeks
(Richardson and Vepraskas, 2001). There is a lag between the onset of saturation and
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
the onset of Fe reduction, and the length of the lag period depends on both soil
temperature and organic matter percentage (Richardson and Vepraskas, 2001).
The oxidation of Fe can occur quickly. Laboratory experiments have shown that after
eight hours approximately 78% of the ferrous iron had oxidized at 20° C while
approximately 60% of the iron had oxidized in three hours (Richardson and Vepraskas,
2001).
A reduced matrix requires that the ferric iron cations in oxides or hydroxides to be
reduced. Iron depletions require the same conditions as a reduced matrix and that the
solubilized ferrous iron has moved to another portion of the soil. The formation of redox
concentrations requires the solubilized iron from one area of the soil to become oxidized
in another areas of the soil, forming Fe masses, pore linings, or nodules. The time
required to form a reduced matrix has not been determined (Richardson and
Vepraskas, 2001).
Oxidized rhizospheres are another characteristic of mineral wetland soils. They result
from the capacity of many hydrophytes to transport oxygen through above-ground
stems and leaves to below-ground roots. Mineral soils that are seasonally flooded,
particularly by alternate wetting and drying, develop spots of highly oxidized materials
called redox (redoximorphic) concentrations. Redox concentrations are orange/reddish-brown
due to iron, or dark reddish-brown/black spots due to manganese. Redox
concentrations are relatively insoluble, enabling them to remain in soil long after it has
been drained (Mitsch and Gosselink, 2000).
Another extremely important factor in the development of soils is the development of
vegetation. Bare exposed soil has a much slower rate of infiltration and a higher rate of
runoff than soil with established vegetation. As vegetation becomes established it
performs the following functions:
��� reduces the amount of soil erosion
• retains water on the site for longer periods, thus increasing the time for infiltration
• forms an insulating layer that retains moisture in the soil
• provides food and cover thereby promoting the growth of micro and macro
organisms.
In addition to these functions, as the roots develop in the soil and development of soil
structure ensues, the following benefits are realized:
• increased porosity and water infiltration
• subsurface accumulation of organic matter and improved water holding capacity
• creation of pathways for micro and macro organisms and nutrients to enter the
soil.
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
While these functions are listed separately, they are interdependent and self promoting.
The development of soils and plants will continually compliment one another even after
the wetland has reached steady state.
Wetland Soils – Current Versus Relict Redoximorphic Features
Redox concentrations indicate where oxidation has occurred in the past. By
themselves, these features give no indication of how long a soil has been saturated and
reduced. A relict reduction feature is one that has formed in the past and persists in the
soil where it can no longer form today, thus giving the impression a soil is wetter than it
really is. Redoximorphic features that are either redox depletions or redox
concentrations are the most likely morphological features to be relict. The reduced
matrix must be kept reduced and can never be relict. Any time a morphological feature,
which had to form along a macropore, is found in the matrix or away from a pore, it can
be assumed that it did not form recently and should be considered relict. When redox
concentrations form, they have diffuse boundaries, sometimes seen as a halo or ring,
around the iron concentration. Diffuse boundaries are assumed to indicate that the
feature is forming or has formed in the recent past and is reflecting current hydrologic
conditions. When redox concentrations begin to dissolve, or are mixed into the matrix,
they acquire sharp boundaries within the matrix, and are thus considered features that
are no longer forming, or relict (Richardson and Vepraskas, 2001).
Occasionally morphological features do not form in soils that are seasonally saturated
and reduced, especially floodplain soils. The reasons for this are not completely
understood, but probably relate to the fact that little Fe reduction occurs, possible due to
one or more of the following: low amounts of organic carbon at the time of saturation, a
high pH, high levels of manganese oxides in the soil, or large amounts of dissolved
oxygen in the water (Richardson and Vepraskas, 2001).
LITTLE SUGAR CREEK MITIGATION SITE
The Little Sugar Creek Mitigation Site occurs within the Charlotte Belt which is
composed of igneous and metamorphic rocks covered by regolith consisting of
weathered in place residuum and soil. Field activities revealed that bedrock on site is
overlain by 10 to 15 feet of clayey soil at the surface with saprolite underneath. The
landscape is characterized by a low floodplain with clay ridges, small depressions, and
relict stream channels (ESI, 1995).
The soils were mapped by the NRCS as being dominated by the Monacan mapping
unit. These are nearly level, somewhat poorly drained soils that have a predominantly
loamy subsoil and were formed in fluvial sediment on floodplains (Soil Conservation
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
Service, 1980). The construction plan called for the removal and stockpiling of the top
six inches of the soil for replacement once the grading was completed.
Personnel from The Catena Group, Inc. visited the site on October 20, 2003. A hand
auger was used to perform detailed soil boring analyses adjacent to four groundwater
monitoring gauges, LSC 4, 6, 8, and 11. A detailed description of each is included in
Attachment A. The first profile, Soil Profile 1, was performed at LSC 6, which met the
hydrologic success criteria for greater than 12.5% of the growing season in 2002.
The soil at LSC 6 showed clear evidence of recent development of redoximorphic
features near the soil surface. There were both concentrations and depletions in the top
13 inches, which also corresponded with the effective rooting depth. In the horizons
below the root zone, only areas of concentrations were found, including manganese
masses, until the C3 horizon, at a depth of 51+ inches, where depletions of chroma 2
began.
The soil profile at LSC 6 is fluvial in origin with little development. However, the fact that
areas of depletions are present in the surface horizons (in correlation with the 13 inch
effective rooting depth), yet not below this level, indicates that this soil is only just
beginning to develop. It is anticipated that as the vegetation continues to establish
itself, the soil will continue its development. This will result in the development of
improved infiltration and wetter conditions for the reasons previously detailed in this
report.
Soil Profile 2 was taken adjacent to LSC-4, which thus far has had a hydrologic regime
of less than 5% of the growing season. This soil has developed from residuum, as
opposed to fluvial sediments. In this soil, areas of depletions and concentrations are
evident throughout the soil profile in contrast and abundance typical of more well
developed soils.
The surface horizon of Soil Profile 2 is 10 inches thick and has areas of concentrations
and depletions. The subsurface horizon immediately beneath the surface horizon
exhibits the same colors and features except for the lack of depletions. This is the
same trend noted in Soil Profile 1. However, in Soil Profile 2 the depletions were few
and faint while those in Soil Profile 1 were common and distinct, which corresponds well
with the slightly reduced hydrologic regime registered near LSC-4. Nevertheless, the
important item of note is that this area also appears to be developing hydric soil, albeit
at a slower pace than LSC-6, and assuming conditions remain constant, the area is
expected to become wetter over time.
Soil Profile 3 was placed near LSC-8, which in 2002 met the wetland hydrology criteria
for 12.3% of the growing season. This profile exhibits the same features and
characteristics as those in Soil Profile 1, except that the development of the surface
horizon(s) is even more pronounced than the subsurface horizons.
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December 2003
Soil Profile 4 was taken near LSC-11, which in 2002 met the wetland hydrology for 6.8%
of the growing season. The spreading of topsoil after grading was completed is clearly
evident at this site. The topsoil layer is 8 inches and is immediately underlain by parent
material. However, once again, areas of concentration and depletions are evident in the
topsoil. While this soil will also continue to develop, it is anticipated that it will take
considerably longer since the underlying parent material is a medium that is more
difficult to weather and develop than the soil found in other areas of the site.
MALLARD CREEK MITIGATION SITE
Less design information is available on the Mallard Creek Mitigation Site, but the
information obtained suggests that the site was graded down to where the average
ground water table exists, as much as 24-inches in some locations. The well data over
two years in the late 1990’s indicates that Site 1 met the wetland hydrology
requirements while Site 2 was failing in some areas and successful in others.
Personnel from The Catena Group, Inc. visited the site on October 20, 2003. A hand
auger was used to perform detailed soil boring analyses adjacent to three monitoring
gauges, MW- 2, 5, and 8. The detailed description of each is included in Attachment B.
The first profile, Soil Profile 5, was taken at MW-2 in Site 1. This profile exhibited more
hydric features than any of the other profiles. As might be expected, this area has
proven to be the wettest area in either mitigation site, based on groundwater gauge
data. This soil is developing from alluvial sediments and actually revealed a buried
hydric soil horizon at 41 inches. Also interesting to note is the lushness and density of
the vegetation throughout this site when compared with the vegetation from the others.
Soil Profiles 6 and 7 were performed in Site 2 at MW-8 and MW-5, respectively. The
most obvious difference between profile 5 and profiles 6 and 7 is that these soils are
developing from residuum. This soil was graded down to the target elevation without
any topsoil placed back over the top. Newly formed redoximorphic features are much
more difficult to discern in these profiles since they are developing in a soil medium that
already contained both relict and recently developed redoximorphic features.
Nevertheless, there appears to be some evidence that these soils are beginning to
develop such as small manganese concretions and oxidized rhizospheres.
DISCUSSION
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December 2003
The soils at both the Little Sugar Creek and Mallard Creek Mitigation Sites exhibit signs
of recent soil development that is occurring at least partially under hydric conditions.
Sites that have been consistently wetter exhibit more hydric features that are easier to
discern than those which have been drier. This does NOT necessarily indicate that
these wetter areas are simply exposed to longer periods of inundation. There are likely
a multitude of other factors, such as better soil structure or more organic matter in the
soil, that are causing differences in hydroperiod.
Stolt et al. (2000) note other factors that often impact soils in created wetlands:
1. As the top soil was removed and reapplied once grading was completed, the soil
profiles were altered in a way that may be hindering the steady pace of hydric
soil development.
2. Soils of constructed wetlands are often higher in temperature due to the lack of
vegetation and organic matter, and possibly drier conditions. This leads to faster
microbial activity and less accumulation of organic matter.
3. The water table rises and falls more quickly in constructed wetlands than in
natural wetlands. This may be due to the lack of organic matter and soil
structure. Soils high in organic matter have higher water holding capacities,
which, in turn, improve reducing conditions.
4. In areas that are graded down, the exposed soil layer has not had the same
exposure to the level of organic acids and intensity of weathering as subsoil in a
natural wetland.
The effect of vegetation cannot be understated. Plants add organic matter and increase
structure (through root growth) so that more water can infiltrate and percolate down
through the soil profile. As plants die and detritus is incorporated into the soil profile by
microorganisms and other fauna, the organic matter content increases, increasing water
holding capacity and structure. This process takes time. Initially, more surface water
will run off then infiltrate into the soil. Once plants are established and the amount of
organic matter starts to increase, more water will infiltrate into the soil, the water holding
capacity will continue to increase, and the soils will start to display more hydric
indicators.
The soil profiles show that recently developed redoximorphic features are present.
While there is no guarantee that these soils will eventually become hydric, they need
more time to develop before any conclusions can be reached. All wetlands take time to
form, especially constructed wetlands. They should not be expected to form quickly. If
the desired hydrology takes longer than expected to become established, so will hydric
soils and hydrophytic plants. This does not necessarily mean, however, that these
mitigation sites are not achieving some of the desired functions that they were intended
to perform. They both capture storm water runoff from nearby roadways, and the Little
Sugar Creek site also retains water from the nearby shopping mall/hospital complex.
These functions should not be overlooked while these sites continue to develop.
TCG - Mitigation Site Soil Analysis
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December 2003
ATTACHMENT A
Little Sugar Creek Soil Profiles
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
Soil Profile 1 (LSC-6)
A 0-7 inches; dark yellowish brown (10YR 3/4) silt loam with common distinct
strong brown (7.5YR 5/8) concentrations and common distinct brown (10YR
4/3) concentrations; friable, medium, subangular blocky structure breaking to
coarse granular structure.
Bw1 7-13 inches; strong brown (7.5YR 5/6) sandy loam with few prominent dark red
(2.5YR 3/6) concentrations and common distinct light yellowish brown (10YR
6/4) depletions; friable, medium subangular blocky structure. Effective rooting
depth 13 inches.
Bw2 13-24 inches; strong brown (7.5YR 5/6) sandy loam with few distinct yellowish
red (5YR 5/8) concentrations; very friable, subangular blocky structure. Hard
manganese concretions present.
C1 24-38 inches; yellowish brown (10YR 5/6) sandy loam; massive structure. 20%
manganese concretions.
C2 38-51 inches; yellowish brown (10YR 5/6) sandy loam, massive structure. 25%
hard manganese concretions and soft manganese masses.
C3 51-60+ inches; light yellowish brown (10YR 6/4) sandy loam with few distinct
light brownish gray (10YR 6/2) depletions; massive structure.
Soil Profile 2 (LSC-4)
A1 0-10 inches; dark yellowish brown (10YR 4/6) fine sandy loam with common
distinct strong brown (7.5YR 4/6) concentrations and few faint dark yellowish
brown (10YR 4/4) depletions; friable, granular structure.
A2 10-16 inches; dark yellowish brown (10YR 4/6) fine sandy loam with common
faint strong brown (7.5YYR 4/6) concentrations; very friable, granular structure.
Effective rooting depth 15 inches.
EB 16-28 inches; strong brown (7.5YR 4/6) sandy loam with common distinct
brown (10YR 4/3) depletions; very friable, coarse subangular blocky structure.
Btg1 28-45 inches; brown (7.5YR 4/4) clay loam with common faint strong brown
(7.5YR 4/6) concentrations and common distinct dark grayish brown (10YR 4/2)
depletions; firm, subangular blocky structure.
Btg2 45-60+ inches; brown (7.5YR 4/4) clay with common faint strong brown (7.5YR
4/6) concentrations and many distinct dark graying brown (10YR 4/2)
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December 2003
depletions; firm, subangular blocky structure. Common soft manganese
masses.
Soil Profile 3 (LSC-8)
A 0-3 inches; dark yellowish brown (10YR 4/4) sandy loam with common distinct
strong brown (7.5YR 4/6) concentrations and few faint brown (10YR 4/3)
depletions; friable, subangular blocky breaking to granular structure.
Bw 3-9 inches; dark yellowish brown (10YR 4/4) clay loam with few distinct strong
brown (7.5YR 5/6) concentrations and common distinct dark grayish brown
(10YR 4/2) depletions; friable, subangular blocky structure. Effective rooting
depth 10 inches.
BC 9-22 inches; dark yellowish brown (10YR 4/4) sandy loam, very friable, weak
subangular blocky structure.
C 22-60+ inches; dark yellowish brown (10YR 4/6) sandy loam; massive
structure.
Soil Profile 4 (LSC-11)
A 0-8 inches; yellowish brown (10YR 5/4) clay loam with few distinct strong brown
(7.5YR 5/8) concentrations and common faint brown (10YR 5/3) depletions;
friable, subangular blocky structure. Effective rooting depth 8 inches.
2C 8+ inches; parent material.
TCG - Mitigation Site Soil Analysis
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December 2003
ATTACHMENT B
Mallard Creek Soil Profiles
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Little Sugar Creek / Mallard Creek
December 2003
Soil Profile 5 (MW-2)
A 0-6 inches; dark yellowish brown (10YR 4/4) silt loam with common distinct
grayish brown (10YR 5/2) depletions and few distinct strong brown (7.5YR 4/6)
concentrations; friable, subangular blocky structure.
Bw 6-16 inches; dark yellowish brown (10YR 4/4) clay loam with common distinct
grayish brown (10YR 5/2) depletions, few distinct strong brown (7.5YR 4/6)
concentrations, and few prominent red (2.5YR 4/6) concentrations; friable,
subangular blocky structure. Effective rooting depth 12 inches.
2C 16-22 inches; dark yellowish brown (10YR 4/4) sandy clay loam with many
distinct grayish brown (2.5Y 5/2) depletions and common distinct yellowish red
(5YR 4/6) concentrations; friable, subangular blocky structure.
3Cg 22-30 inches; grayish brown (2.5Y 5/2) silt loam with common prominent
yellowish red (5YR 4/6) concentrations; friable, subangular blocky structure.
4C 30-41 inches; dark yellowish brown (10YR 4/4) sandy clay with common distinct
grayish brown (10YR 5/2) depletions; firm, subangular blocky structure.
Ab 41-55 inches; gray (10YR 5/1) clay loam with common distinct strong brown
(7.5YR 5/8) concentrations; firm, subangular blocky structure.
Bgb 55-60+ inches; gray (10YR 5/1) sandy loam with few distinct yellowish brown
(10YR 5/8) concentrations.
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December 2003
Soil Profile 2 (MW-8)
AB 0-12 inches; strong brown (7.5YR 4/6) clay loam with many distinct brown
(10YR 5/3) depletions; friable, coarse, subangular blocky structure. Common,
small manganese concretions.
Bt 12-26 inches; brown (10YR 5/3) clay loam with many distinct yellowish red
(5YR 4/6) concentrations; friable, subangular blocky structure.
Btg1 26-39 inches; gray (10YR 5/1) clay with many distinct dark yellowish brown
(10YR 4/6) concentrations and common distinct yellowish brown (10YR 5/8)
concentrations; friable, subangular blocky structure.
Btg2 39-48 inches; gray (10YR 6/1) clay with many distinct brownish yellow (10YR
6/8) concentrations; very firm, subangular blocky structure.
Btg3 48+ inches; bluish gray (5PB 6/1) clay with many prominent yellowish brown
(10YR 5/8) concentrations; very firm, subangular blocky structure. Few
manganese concretions present.
Soil Profile 3 (MW-5)
AC 0-6 inches; brown (7.5YR 4/4) clay loam with many distinct strong brown
(7.5YR 5/6) concentrations and common distinct brown (10YR 4/3) depletions;
friable, subangular blocky structure.
TCG - Mitigation Site Soil Analysis
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December 2003
TCG - Mitigation Site Soil Analysis
Little Sugar Creek / Mallard Creek
December 2003
References
Correspondence about Mallard Creek Mitigation Site through notes from the North
Carolina Department of Transportation. 1996 – 2000.
Environmental Services, Inc. 1995. Compensatory Mitigation Plan for Little Sugar
Creek Site Charlotte Outer Loop (R-211-DA) Mecklenburg County, North Carolina.
Prepared for the North Carolina Department of Transportation, Raleigh, North Carolina.
Mitsch, W.J. and Gosselink, J.G. 2000. Wetlands, 3rd Ed. John Wiley and Sons, Inc.,
New York, New York.
Mitsch, W.J. and Wilson, R.F. 1996. Improving the success of wetland creation and
restoration with know-how, time, and self-design. Ecological Applications. 6 77-83.
Richardson, J.L. and Vepraskas, M.J. 2001. Wetland Soils. Genesis, hydrology,
landscapes, and classification. Lewis Publishers, Boca Raton.
Stolt, M.H., Genthner, M.H., Daniels, W.L., Groover, V.A., Nagle, S., and Haering, K.C.
2000. Comparison of soil and other environmental conditions in constructed and
adjacent palustrine reference wetlands. Wetlands. 20 671-683.
United States Department of Agriculture. 1980. Soil Survey of Mecklenburg County,
North Carolina. National Cooperative Soil Survey.