Hydrology and water quality of seepage slope wetlands on the SC Coastal Plain
Daniel L. Tufford
Department of Biological Sciences, University of South Carolina, Columbia, SC 29208
This poster provides preliminary results from one component of a
broader project to begin a descriptive and systems ecological study
of seepage wetlands on the South Carolina Coastal Plain.
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A shallow well was placed adjacent to each seep. The wells (Figs. 2
and 3) were constructed following the guidelines from Sprecher
(1993) as modified by Sprecher (2000). The wells range from 1.2 to
1.4 m deep. Each well has a Global WL15 water level recorder with
a 1 hour recording interval. The wells were purged with a bailer
several times in the weeks immediately following installation. An
Onset tipping bucket recording rain gauge was deployed in a
nearby location with no canopy.
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Precipitation - cm
Water table depth - m
October 20 - 26, 2005
July 28 - August 1, 2005
Fig 4. Precipitation and water table depth at one well in
Beidler Forest during summer and autumn 2005.
July 01 - 06, 2005
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Once installed and stable the wells were visited seasonally to
retrieve water level data, take water quality field parameter
measurements with a YSI 600XLM sonde, and collect water
samples for laboratory analysis. The wells were purged prior to
taking YSI measurements and collecting water for analysis. The
water was analyzed for nitrogen and phosphorus fractions and
dissolved organic carbon (DOC) at an SCDHEC certified
commercial laboratory.
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Seepage wetlands occur at the base of slopes and bluffs, typically at
the outer edge of a floodplain or stream corridor. Unlike riverine
wetlands, however, these receive most of their water from seeps
and springs that discharge groundwater flow from adjacent upslope
land. Seepage wetlands are relatively common on the Southeastern
Coastal Plain; in fact they are a dominant feature on many of the
landscapes in which they occur. It is believed they serve important
roles in local and regional biodiversity, water quality, and
biogeochemical cycling. These conclusions are based on a small
amount of field data and inference from other wetlands on the
coastal plain. It is likely that because the surrounding uplands are
the primary source of water, these habitats are especially vulnerable
to the effects of nearby land management activities. The nature and
extent of the vulnerability is unknown.
Results
Wells, instrumentation, and
sampling
Water table depth - m
Introduction
Discussion
October 21 - 26, 2005
Fig 5. Precipitation and water table depth at one well in
Wannamaker Nature Preserve during summer and autumn 2005.
Table 2. Seasonal dissolved oxygen (DO – mg/l) and
oxidation reduction potential (ORP – mV) in the four wells.
Study sites
For the initial study we selected two seeps at each of two sites (Fig.
1; Table 1). The objective was to facilitate assessment of variability
both within a site and among sites. One site is owned by National
Audubon Society; the other by Charleston Natural History Society,
a local chapter of the national organization.
Fig. 2. Monitoring well
profile from Sprecher
(1993). The wells in
this project did not
include the grout layer
or well point, as
suggested in
Sprecher (2000).
Well
Summer
DO
ORP
1.59
142
0.98
-41
3.46
196
1.08
4
BF1
BF2
WNP1
WNP2
Autumn
DO
ORP
8.47
151
2.76
213
14.22
110
7.61
93
DO
11.09
10.26
6.41
6.36
ORP
93
136
125
110
DOC - mg/l
BF02
WNP01
2
WNP02
1
Fig. 6. Seasonal
dissolved organic
carbon
concentrations in
the four wells.
0
Sum
Aut
Win
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BF01
Fig. 1. Two seeps are
located at Francis Beidler
Forest (1, Dorchester
County, Four Holes
Swamp watershed) and
two are at Wannamaker
Nature Preserve (2,
Calhoun County, Halfway
Swamp Creek watershed).
Response to rain events is clearly different between the two sites.
The BF hydrograph has a steep rise and steady recession, typical of
headwater streams. In this case the rise is caused by precipitation in
the immediate vicinity of the well, while the recession curve and
duration indicates lateral flow from the upland. At the WNP well
both the rise and initial recession are steep. There appears to be a
secondary hydrograph when additional water reaches the well. This
secondary flow is substantial and is capable of displacing the
timing of the diurnal peak. The differences between the two sites
are probably the result of different upland topography. The WNP
site has much higher bluffs (Table 1), which increases travel time
within the soil layer.
There are seasonal differences in water quality as well as
differences between wells at each site. The water tends to be much
lower in DO concentration during the summer (July 27) than other
seasons in all wells, with differences within site as well. The
within-site differences persist in the autumn although
concentrations increase. By winter the concentrations are relatively
the same. Similar comments apply to redox potential.
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BF01
The Beidler Forest (BF) site is old-growth cypress-tupelo swamp,
although the upland adjacent to the study seeps is second- or thirdgrowth mixed hardwood. The Wannamaker Nature Preserve (WNP)
site is second- or third-growth mature bottomland hardwood on the
floodplain and mature upland hardwood upslope from the seeps.
The Preserve encompasses a working farm that has been out of
production for 15-20 years.
Winter
Seasonal hydrology follows expected patterns in these wells.
During summer there is a diurnal cycle in water table depth. This is
caused by evapotranspiration that increases during early morning to
a daily peak in the afternoon. This signal is reduced by autumn
(November 3), which reflects the senescence of many plants and
overall reduction in biotic activity. During winter (data not shown)
this signal is gone.
Fig. 7. Seasonal
ammonia
concentrations in
the four wells.
BF02
NH3 - mg/l
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WNP01
WNP02
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0
Sum
Aut
Win
DOC appears to decrease from summer into winter. This is
consistent with less microbial activity as temperatures moderate.
For both nitrogen and phosphorus (not shown) the organic fraction
is substantially larger than the inorganic fraction. The seasonal
pattern of TN appears to be different between wells at the same site.
This could be another manifestation of differences seen in the DO
and redox potential. Additional investigation is needed.
Literature cited
Sprecher, S. W. 1993. Installing Monitoring Wells/Piezometers in
Wetlands. WRP Technical Note HY-IA-3.1, US Army Corps
of Engineers, Waterways Experiment Station, Vicksburg,
MS.
Sprecher, S. W. 2000. Installing Monitoring Wells/Piezometers in
Wetlands. ERDC TN-WRAP-00-02, US Army Research and
Development Center, Vicksburg, MS.
4
Fig. 8. Seasonal
total nitrogen
concentrations in
the four wells.
Total nitrogen - mg/l
BF01
Table 1. Physical descriptions for the two study sites. At each
site the wells are in seeps that are approximately 75 m apart.
(TBD – to be determined)
BF02
3
WNP01
WNP02
2
1
Acknowledgments
This work was funded by Audubon South Carolina and The Nature
Conservancy. Special thanks go to Norman Brunswig, John Nelson, Steve
Bennett, Kristin Harrison, and Dick Watkins.
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Location
Beidler Forest
Wannamaker Nature Preserve
Bluff elevation (m) Bluff slope (deg)
8
13
24
27
Soils
Osier
TBD
Sum
Fig. 3. One of the wells in Beidler Forest.
Aut
Win
For further information
Please contact Dan Tufford (phone: 803-777-3292; e-mail:
[email protected]) for more information.