Citation:

BURKE, R. A. AND J. MOLINERO. DISSOLVED ORGANIC CARBON AND DISSOLVED CARBON DIOXIDE CONCENTRATIONS AND EXPORT IN GEORGIA PIEDMONT HEADWATER STREAMS. Presented at Gordon Research Conference on Catchment Science: Interactions of Hydrology, Biology, and Geochemistry, New London, NH, July 08 - 13, 2007.

Impact/Purpose:

The overall objective of this task is to identify or develop useful indicators of organic waste enrichment in aquatic systems that are easily measured and based on basic underlying ecosystem processes so that they will be widely applicable. These activities will primarily contribute to an APG within Long Term Goal 2 of the Water Quality Research Program Multiyear Plan: the 2008 APG on equipping EPA Regions, States, and Tribes with knowledge, skills and tools to determine the causes of impairments for freshwater and coastal systems required in various regulations and will also contribute to EPA Strategic Plan 2003-2008 Sub-objective 2.2.2: Improve Coastal and Ocean Waters. Activities that address the 2008 Water Quality APG will focus primarily on small streams of the Georgia Piedmont, which receive human and agricultural waste inputs. The activities related to EPA Sub-objective 2.2.2 will focus on the nearshore marine ecosystem of the Pacific Ocean, which receives treated wastes from the approximately 15 million people who live in the coastal zone of southern California and northern Baja California, Mexico, and on the nearshore marine ecosystem of the Gulf of California, which receives little anthropogenic pollution. The indicators that will be evaluated or developed will include concentrations of trace gases (N2O, CH4, and CO2), dissolved oxygen (DO), nutrients, and dissolved organic matter (DOM), other key parameters such as temperature, conductivity or salinity, flow rate, alkalinity, and pH, rates of key processes such as denitrification and DO consumption, and stable isotope ratios of various pools and substrates such as plants, animals, sediments, and DO.

Description:

The South Fork Broad River (SFBR) drains about 550 km2 of the Georgia Piedmont. The SFBR watershed is primarily rural and undeveloped although the human population increased by about 25% between 1990 and 2000. Forestry and agriculture are the main land uses. Agriculture consists mainly of pasture and poultry operations. Northern Georgia is a major area of US poultry production and massive amounts of poultry litter are generated, most of which is applied to pastures near the production site. Further, 90% of the homes are on septic tanks. Given all these sources, there is potential for contamination of headwater streams by organic waste contamination. We monitored concentrations of dissolved organic carbon (DOC), dissolved CO2, pH, temperature, flow, and other parameters in 17 SFBR headwater streams on a monthly basis for about a year. We calculated bicarbonate concentrations from the pH and temperature data, and total dissolved carbon (TDC) as the sum of DOC, dissolved CO2, and bicarbonate. Land use in the small watersheds that we studied was derived from the National Land Cover Data database. Mean concentrations of DOC, dissolved CO2, bicarbonate and TDC, and annual DOC export were positively correlated with land cover (% pasture). In contrast, annual export of TDC, dissolved CO2, and bicarbonate were not correlated with land use suggesting that hydrological controls are relatively more important for these parameters. We hypothesize that elevated DOC concentrations and DOC export observed in streams draining watersheds with extensive pasture land use result from input of organic wastes to the soils in excess of terrestrial ecosystem processing capacity. Contamination of streams as a result of the excessive land application of organic wastes is a concern because we observed dissolved oxygen concentrations below the minimum allowed for non-trout waters (4 mg/L) during the summer in some of the streams.

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