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ASSESSING NON-POINT SOURCES OF NITROGEN TO SMALL STREAMS IN THE SOUTH FORK BROAD RIVER WATERSHED (GEORGIA, USA)
Citation:
Molinero, J. AND R A. Burke Jr. ASSESSING NON-POINT SOURCES OF NITROGEN TO SMALL STREAMS IN THE SOUTH FORK BROAD RIVER WATERSHED (GEORGIA, USA). Presented at VII International Congress of Ecology, Seoul, Korea, August 11-18, 2002.
Impact/Purpose:
This research project sets out to design and conduct an assessment of the long-term ecological consequences of alternative watershed management choices. As the first project to be done at this scale using predictive ecological endpoints, we will seek to identify the appropriate components of such an analysis. We will use experience gained in the conduct of this analysis to identify key research and data needs for future analyses. We will extend this analysis beyond previous and ongoing studies in two ways: by incorporating biological endpoints, primarily properties of fish communities, and by introducing the concept of sustainability of ecological state under future scenarios contrasted with the present state of those same ecological resources. Requirements that are identified during the course of this study will permit the recommendation of specific capabilities that should be incorporated in a general modeling system currently under development to support environmental assessments. Finally, the analysis is intended to be of value for establishing environmental management choices that will be beneficial and those that would be detrimental to the sustainability of ecological resources. Specific objectives are listed below:
1. Develop watershed-based modeling systems to forecast the effectiveness of alternative management plans in meeting sediment-related, nutrient-related, pathogen-related, and toxics-related criteria and standards, and biologically-based criteria and standards; and
2. Develop and maintain a comprehensive technical support capability that directly links environmental TMDL exposure research activities and products for the EPA Office of Water, EPA Regional Offices, and the States to be used for implementation of policy, regulatory development, remediation, and enforcement needs.
Description:
The National Land Cover Data (NLCD) is a land cover classification derived from Landsat Thematic Mapper satellite data collected in the early to mid-1990s. In this work, land use coverages calculated from the NLCD database are used to assess the impact of non-point sources on the nitrogen concentrations in small headwater streams. Dissolved organic nitrogen (DON) and particulate nitrogen (PN), which are not included in most nutrient studies, are also considered in this work. The Broad River is located in northeast Georgia and flows from the Appalachian mountains to its confluence with the Savannah River at the Clarks Hill/Strom Thurmond reservoir. The South Fork Broad River (SFBR) is a 128 km length tributary to the Broad River located in the southwest part of its watershed. The SFBR watershed is about 556 km2 and it is primarily rural and remains in a largely natural state. Agriculture and pasture land are the main uses throughout the valley and there are also some managed forests. Industrial use in the watershed is limited to a few granite quarries. Twelve headwater watersheds ranging from 0.5 to 3.4 km2 were selected. Percentages of forested land, agricultural and pasture land, residential areas, wetlands and open water surfaces within the watershed were calculated from the NLCD database. Water samples were collected monthly from November 2001 to March 2002 at the outlet of each watershed. Samples for dissolved inorganic and organic nitrogen were filtered with 0.45 ?m membrane filters. Oxidized nitrogen (nitrate + nitrite) was determined by UV detection. DON and PN were determined by persulfate digestion followed by UV detection. Ammonia was determined with an Accumet ammonia electrode. Linear models relating land uses to the nitrogen concentrations in the streams developed by step-wise regression. The lowest total nitrogen (TN) concentrations were found in forested streams (0.310-0.318 mg N/l). TN concentrations were high in streams draining developed areas (0.606-2.643 mg N/l) and pasture and agricultural land (1.334-2.623 mg N/l) Finally, streams in watersheds with mixed land uses showed intermediate TN concentrations (0.597-1.232 mg N/l). Up to 70 % of the TN in streams draining residential areas was dissolved inorganic nitrogen (DIN). In contrast, streams in forested watershed had less nitrogen (45 %) in inorganic form and about twice more nitrogen (45 %) in organic form than streams in residential areas. Streams in agricultural and pasture land dominated watersheds had about twice more nitrogen (15 %) in particulate form than in either forested or residential watersheds. The amount of forested land within the watershed was the best predictor to the concentrations of the different forms of nitrogen in the streams. These observations support that land uses within the watershed largely influences both nitrogen concentrations and forms in stream water. Also, the impact of land uses on nitrogen concentrations in streams at a local scale can be assessed using data derived from the NLCD database.