Geochemical characteristics of trace elements in sediments of Dongting Lake, central China

water to this reservoir, and within the two reservoirs. Those isotopic measurements indicate the rapid change of natural sources of nitrate to one indicative of anthropogenic influences from inputs of animal manure and septic waste. Although the isotopic measurements suggest that animal and septic wastes are a primary source of nutrients, measurements of the ratio of nitrogen to phosphorus are more indicative of row cropping practices. Options for reduction of nutrient loads included changing the management practices of the aqua culture, installation of new sewage treatment systems, especially in the one major urbanized area of the upper watershed, and agricultural man.