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Table 7-1. Effectiveness of Wetlands and Riparian Areas for NPS Pollution Control
1 - Tar River Basin, North Carolina
Riparian Forests
This study looks at how various soil types affect the buffer width necessary
for effectiveness of riparian forests to reduce loadings of agricultural
nonpoint source pollutants.
- A hypothetical buffer with a width of 30 m and designed to remove 90% of
the nitrate nitrogen from runoff volumes typical of 50 acres of row crop on
relatively poorly drained soils was used as a standard.
- Udic upland soils and sandy entisols met or exceeded these standards.
- The study also concluded that slope gradient was the most important
contributor to the variation in effectiveness. Phillips, J.D. 1989. Nonpoint
Source Pollution Control Effectiveness of Riparian Forests Along a Coastal
Plain River. Journal of Hydrology, 110 (1989):221-237.
2 - Lake Tahoe, Nevada
Riparian
Three years of research on a headwaters watershed has shown this area to be
capable of removing over 99% of the incoming nitrate nitrogen. Wetlands and
riparian areas in a watershed appear to be able to "clean up"
nitrate-containing waters with a very high degree of efficiency and are of
major value in providing natural pollution controls for sensitive waters.
Rhodes, J., C.M. Skau, D. Greenlee, and D. Brown. 1985. Quantification of
Nitrate Uptake by Riparian Forests and Wetlands in an Undisturbed Headwaters
Watershed. In Riparian Ecosystems and Their Management: Reconciling
Conflicting Issues. USDA Forest Service GTR RM-120, pp. 175-179.
3 - Atchafalaya, Louisiana
Riparian
Overflow areas in the Atchafalaya Basin had large areal net exports of total
nitrogen (predominantly organic nitrogen) and dissolved organic carbon but
acted as a sink for phosphorus. Ammonia levels increased dramatically during
the summer. The Atchafalaya Basin floodway acted as a sink for total organic
carbon mainly through particulate organic carbon (POC). Net export of dissolved
organic carbon was very similar to that of POC for all three areas. Lambou,
V.W. 1985. Aquatic Organic Carbon and Nutrient Fluxes, Water Quality, and
Aquatic Productivity in the Atchafalaya Basin, Louisiana. In Riparian
Ecosystems and Their Management: Reconciling Conflicting Issues. USDA
Forest Service GTR RM-120, pp. 180-185.
4 - Wyoming
Riparian
The Green River drains 12,000 mi2 of western Wyoming and northern Utah and
incorporates a diverse spectrum of geology, topography, soils, and climate.
Land use is predominantly range and forest. A multiple regression model was
used to associate various riparian and nonriparian basin attributes (geologic
substrate, land use, channel slope, etc.) with previous measurements of
phosphorus, nitrate, and dissolved solids. Fannin,T.E., M. Parker, and T.J.
Maret. 1985. Multiple Regression Analysis for Evaluating Non-point Source
Contributions to Water Quality in the Green River, Wyoming. In Riparian
Ecosystems and Their Management: Reconciling Conflicting Issues. USDA
Forest Service GTR RM-120, pp. 201-205.
5 - Rhode River Subwater-shed, Maryland
Riparian
A case study focusing on the hydrology and below-ground processing of
nitrate and sulfate was conducted on a riparian forest wetland. Nitrate and
sulfate entered the wetland from cropland ground-water drainage and from direct
precipitation. Data collected for 3 years to construct monthly mass balances of
the fluxes of nitrate and sulfate into and out of the soils of the wetland
showed:
- Averages of 86% of nitrate inputs were removed in the wetland.
- Averages of 25% of sulfates were removed in the wetland.
- Annual removal of nitrates varied from 87% in the first year to 84% in the
second year.
- Annual removal of sulfate varied from 13% in the second year to 43% in the
third year.
- On average, inputs of nitrate and sulfate were highest in the winter.
- Nitrate outputs were always highest in the winter.
- Nitrate removal was always highest in the fall (average of 96%) when input
fluxes were lowest and lowest in winter (average of 81%) when input fluxes were
highest. Correll, D.L., and D.E. Weller. 1989. Factors Limiting Processes in
Freshwater: An Agricultural Primary Stream Riparian Forest. In Freshwater
Wetlands and Wildlife, ed. R.R. Sharitz and J.W. Gibbons, pp. 9-23. U.S.
Department of Energy, Office of Science and Technology, Oak Ridge, Tennessee.
DOE Symposium Series #61.
6 - Carmel River, California
Riparian
Ground water is closely coupled with streamflow to maintain water supply to
riparian vegetation, particularly where precipitation is seasonal. A case study
is presented where Mediterranean climate and ground-water extraction are linked
with the decline of riparian vegetation and subsequent severe bank erosion on
the Carmel River. Groenveld, D. P., and E. Griepentrog. 1985. Interdependence
of Groundwater, Riparian Vegetation, and Streambank Stability: A Case Study.
In Riparian Ecosystems and their Management: Reconciling Conflicting
Issues. USDA Forest Service GTR RM-120, pp. 201-205.
7 - Cashe River, Arkansas
Riparian
A long-term study is being conducted to determine the chemical and
hydrological functions of bottomland hardwood wetlands. Hydrologic gauging
stations have been established at inflow and outflow points on the river, and
over 25 chemical constituents have been measured. Preliminary results for the
1988 water year indicated:
- Retention of total and inorganic suspended solids and nitrate;
- Exportation of organic suspended solids, total and dissolved organic
carbon, inorganic carbon, total phosphorus, soluble reactive phosphorus,
ammonia, and total Kjeldahl nitrogen;
- All measured constituents were exported during low water when there was
limited contact between the river and the wetlands; and
- All measured constituents were retained when the Cypress-Tupelo part of the
floodplain was inundated. Kleiss, B. et al. 1989. Modification of Riverine
Water Quality by an Adjacent Bottomland Hardwood Wetland. In Wetlands:
Concerns and Successes, pp. 429-438. American Water Resources
Association.
8Scotsman Valley, New Zealand
Riparian
Nitrate removal in riparian areas was determined using a mass balance
procedure in a small New Zealand headwater stream. The results of 12 surveys
showed:
- The majority of nitrate removal occurred in riparian organic soils
(56-100%) even though the soils occupied only 12% of the stream's border.
- The disproportionate role of organic soils in removing nitrate was due in
part to their location in the riparian zone. A high percentage (37-81%) of
ground water flowed through these areas on its passage to the stream.
- Anoxic conditions and high concentrations of denitrifying enzymes and
available carbon in the soils also contributed to the role of the organic soils
in removing nitrates. Cooper, A.B. 1990. Nitrate Depletion in the Riparian Zone
and Stream Channel of a Small Headwater Catchment. Hydrobiologia,
202:13-26.
9 - Wye Island, Maryland
Riparian
Changes in nitrate concentrations in ground water between an agricultural
field planted in tall fescue (Festuca arundinacea) and riparian zones
vegetated by leguminous or nonleguminous trees were measured to:
- Determine the effectiveness of riparian vegetation management practices in
the reduction of nitrate concentrations in ground water;
- Identify effects of leguminous and nonleguminous trees on riparian
attenuation of nitrates; and
- Measure the seasonal variability of riparian vegetation's effect on the
chemical composition of ground water.
Based on the analysis of shallow ground-water samples, the following patterns
were observed:
- Ground-water nitrate concentrations beneath non-leguminous riparian trees
decreased toward the shoreline, and removal of the trees resulted in increased
nitrate concentrations.
- Nitrate concentrations did not decrease from the field to the riparian zone
in ground water below leguminous trees, and removal of the trees resulted in
decreased ground-water nitrate concentrations.
- Maximum attenuation of nitrate concentrations occurred in the fall and
winter under non-leguminous trees. James, B.R., B.B. Bagley, and P.H.
Gallagher, P.H. 1990. Riparian Zone Vegetation Effects on Nitrate
Concentrations in Shallow Groundwater. Submitted for publication in the
Proceedings of the 1990 Chesapeake Bay Research Conference. University of
Maryland, Soil Chemistry Laboratory, College Park, Maryland.
10 - Little Lost Man Creek, Humboldt, California
Riparian
Nitrate retention was evaluated in a third-order stream under background
conditions and during four intervals of modified nitrate concentration caused
by nutrient amendments or storm-enhanced discharge. Measurements of the stream
response to nitrate loading and storm discharge showed:
- Under normal background conditions, nitrate was exported from the
subsurface (11% greater than input).
- With increased nitrate input, there was an initial 39% reduction from the
subsurface followed by a steady state reduction of 14%.
- During a storm event, the subsurface area exported an increase of 6%.
Triska, F.J., V.C. Kennedy, R.J. Avanzino, G.W. Zellweger, and K.E. Bencala.
1990. In Situ Retention-Transport Response to Nitrate Loading and Storm
Discharge in a Third-Order Stream. Journal of North American Benthological
Society, 9(3):229-239.
11 - Toronto, Ontario, Canada
Riparian
Field enrichments of nitrate in two spring-fed drainage lines showed an
absence of nitrate depletion within the riparian zone of a woodland stream. The
results of the study indicated:
- The efficiency of nitrate removal within the riparian zone may be limited
by short water residence times.
- The characteristics of the substrate and the routes of ground-water
movement are important in determining nitrate attenuation within riparian
zones. Warwick, J., and A.R. Hill. 1988. Nitrate Depletion in the Riparian Zone
in a Small Woodland Stream. Hydrobiologia, 157:231-240.
12 - Little River, Tifton, Georgia Riparian
A study was conducted on riparian forests located adjacent to agricultural
uplands to test their ability to intercept and utilize nutrients (N, P, K, Ca)
transported from these uplands. Tissue nutrient concentrations, nutrient
accretion rates, and production rates of woody plants on these sites were
compared to control sites. Data from this study provide evidence that young
(bloom state) riparian forests within agricultural ecosystems absorb nutrients
lost from agricultural uplands. Fail, J.L. Jr., Haines, B.L., and Todd, R.L.
Undated. Riparian Forest Communities and Their Role in Nutrient Conservation in
an Agricultural Watershed. American Journal of Alternative Agriculture,
II(3):114-120.
13 - Chowan River Watershed, North Carolina
Riparian
A study was conducted to determine the trapping efficiency for sediments
deposited over a 20-year period in the riparian areas of two watersheds. 137CS
data and soil morphology were used to determine areal extent and thickness of
the sediments. Results of the study showed:
- approximately 80% of the sediment measured was deposited in the floodplain
swamp.
- Areater than 50% of the sediment was deposited within the first 100 m
adjacent to cultivated fields.
- aediment delivery estimates indicated that 84% to 90% of the sediment
removed from cultivated fields remained in the riparian areas of a watershed.
Cooper, J.R., J.W. Gilliam, R.B. Daniels, and W.P. Robarge. 1987. Riparian
Areas as Filters for Agriculture Sediment. Soil Science Society of America
Journal, 51(6):417-420.
14 - New Zealand
Riparian
Several recent studies in agricultural fields and forests showed evidence of
significant nitrate removal from drainage water by riparian zones. The results
of these studies showed:
- d typical removal of nitrate of greater than 85% and
- dn increase of nitrate removal by denitrification where greater contact
occurred between leaching nitrate and decaying vegetative matter. Schipper,
L.A., A.B. Cooper, and W.J. Dyck. 1989. Mitigating Non-point Source Nitrate
Pollution by Riparian Zone Denitrification. Forest Research Institute, Rotorua,
New Zealand.
15 - Georgia
Riparian
A streamside, mixed hardwood, riparian forest near Tifton, Georgia, set in
an agricultural watershed was effective in retaining nitrogen (67%), phosphorus
(25%), calcium (42%), and magnesium (22%). Nitrogen was removed from subsurface
water by plant uptake and microbial processes. Riparian land use was also shown
to affect the nutrient removal characteristics of the riparian area. Forested
areas were more effective in nutrient removal than pasture areas, which were
more effective than croplands. Lowrance, R.R., R.L. Todd, and L.E. Asmussen.
1983. Waterborne Nutrient Budgets for the Riparian Zone of an Agricultural
Watershed. Agriculture, Ecosystems and Environment, 10:371-384.
16 - North Carolina
Riparian
Riparian forests are effective as sediment and nutrient (N and P) filters.
The optimal width of a riparian forest for effective filtering is based on the
contributing area, slope, and cultural practices on adjacent fields. Cooper, J.
R., J. W. Gilliam, and T. C. Jacobs. 1986. Riparian Areas as a Control of
Nonpoint Pollutants. In Watershed Research Perspectives, ed. D. Correll,
Smithsonian Institution Press, Washington, DC.
17 - Unknown
Riparian
A riparian forest acted as an efficient sediment trap for most observed flow
rates, but in extreme storm events suspended solids were exported from the
riparian area. Karr, J.R., and O.T. Gorman. 1975. Effects of Land Treatment on
the Aquatic Environment. In U.S. EPA Non-Point Source Pollution Seminar,
pp. 4-1 to 4-18. U.S. Environmental Protection Agency, Washington, DC. EPA
905/9-75-007.
18 - Arkansas
Riparian
The Army Corps of Engineers studied a 20-mile stretch of the Cashe River in
Arkansas where floodplain deposition reduced suspended solids by 50%, nitrates
by 80%, and phosphates by 50%. Stuart, G., and J. Greis. 1991. Role of
Riparian Forests in Water Quality on Agricultural Watersheds.
19 - Maryland
Riparian
Phosphorus export from the forest was nearly evenly divided between surface
runoff (59%) and ground-water flow (41%), for a total P removal of 80%. The
mean annual concentration of dissolved total P changed little in surface
runoff. Most of the concentration changes occurred during the first 19 m of the
riparian forest for both dissolved and particulate pollutants. Dissolved
nitrogen compounds in surface runoff also declined. Total reductions of 79% for
nitrate, 73% for ammonium-N and 62% for organic N were observed. Changes in
mean annual ground-water concentrations indicated that nitrate concentrations
decreased significantly (90-98%) while ammonium-N concentrations increased in
concentration greater than threefold. Again, most of the nitrate loss occurred
within the first 19 m of the riparian forest. Thus it appears that the major
pathway of nitrogen loss from the forest was in subsurface flow (75% of the
total N), with a total removal efficiency of 89% total N. Peterjohn, W.T., and
D.L. Correll. 1984. Nutrient Dynamics in an Agricultural Watershed:
Observations on the Role of a Riparian Forest. Ecology,
65:1466-1475.
20 - France
Riparian
Denitrification explained the reduction of the nitrate load in ground water
beneath the riparian area. Models used to explain the nitrogen dynamics in the
riparian area of the Lounge River indicate that the frequency, intensity, and
duration of flooding influence the nitrogen-removal capacity of the riparian
area.
Three management practices in riparian areas would enhance the
nitrogen-removal characteristics, including:
- fiver flow regulation to enhance flooding in riparian areas, which
increases the waterlogged soil areas along the entire stretch of river;
- feduced land drainage to raise the water table, which increases the
duration and area of waterlogged soils; and
- fecreased deforestation of riparian forests, which maintains the amount of
carbon (i.e., the energetic input that allows for microbial denitrification).
Pinay, G., and H. Decamps. 1988. The Role of Riparian Woods in Regulating
Nitrogen Fluxes Between the Alluvial Aquifer and Aurface Water: A Conceptual
Model. Regulated Rivers: Research and Management, 2:507-516.
21 - Georgia
Riparian
Processes within the riparian area apparently converted primarily inorganic
N (76% nitrate, 6% ammonia, 18% organic N) into primarily organic N (10%
nitrate, 14% ammonia, 76% organic N). Lowrance, R.R., R.L. Todd, and L.E.
Assmussen. 1984. Nutrient Cycling in an Agricultural Watershed: Phreatic
Movement. Journal of Environmental Quality, 13(1):22-27.
22 - North Carolina
Riparian
Subsurface nitrate leaving agricultural fields was reduced by 93% on
average. Jacobs, T.C., and J.W. Gilliam. 1985. Riparian Losses of Nitrate from
Agricultural Drainage Waters. Journal of Environmental Quality,
14(4):472-478.
23 - North Carolina
Riparian
Over the last 20 years, a riparian forest provided a sink for about 50% of
the phosphate washed from cropland. Cooper, J.R., and J.W. Gilliam. 1987.
Phosphorus Redistribution from Cultivated Fields into Riparian Areas. Soil
Science Society of America Journal, 51(6):1600-1604.
24 - Illinois
Riparian
Small streams on agriculture watersheds in Illinois had the greatest water
temperature problems. The removal of shade increased water temperature 10-15
degrees Fahrenheit. Slight increases in water temperature over 60 øF
caused a significant increase in phosphorus release from sediments. Karr, J.R.,
and I.J. Schlosser. 1977. Impact of Nearstream Vegetation and Stream
Morphology on Water Quality and Stream Biota. Ecological Research Series,
EPA-600/3-77-097. U.S. Environmental Protection Agency, Washington, DC.
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