Organic waste contamination indicators in small Georgia Piedmont streams
Burke, Roger A.
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We monitored concentrations of dissolved organic carbon (DOC) and dissolved oxygen (DO), and other parameters in 17 small streams of the South Fork Broad River watershed on a monthly basis for 15 months. We observed a strong inverse relationship between mean DOC and mean DO, and low DO concentrations (2 mg/L) during summer in some of the streams. Elevated DOC levels and corresponding low DO may result from watershed sources of organic wastes and/or nutrients. Potential sources of watershed organic wastes include animal manure applied to the land and/or human wastes from wastewater treatment plants or septic tanks. Here we present estimates of the amounts of organic waste input to these watersheds and evaluate the possible impact of the waste on stream DOC concentrations. Our results suggest that application of poultry litter at recommended rates may impact stream DOC levels if applied to a high enough percentage of the watershed land area. We also present a few measurements of the stable nitrogen isotope ratio of plants growing in the channel and of potential denitrification rate in the sediments of a few of these streams on a few dates shortly after the monthly monitoring ended. These preliminary results suggest that stable nitrogen isotope ratios and potential denitrification rates are positively correlated with estimates of stream watershed human waste loading and thus are potentially effective indicators of waste contamination in these watersheds. In some cases, stable isotopic, potential denitrification rate, and other biogeochemical indicators of organic waste and/or nutrient contamination may be useful to regulators and managers charged with protecting water quality.