DISTINGUISHING BETWEEN ANTHROPOGENIC AND BIOGENIC ORGANICS IN BLACK SHALE DRAINING STREAMS

Organics in water and sediment may be of natural or anthropogenic origin. Anthropogenic organics include products of agricultural and industrial practices. Pesticides, often in the form of organochlorine pesticides, enter water bodies from storm runoff. These pesticides can contaminate the aquatic system and may be toxic to stream organisms. Biogenic organics are products of natural processes such as bedrock weathering and biodegradation. During black shale weathering, high concentrations of organic carbon are released to receiving waters in both dissolved and particulate phases. Increased carbon loading in marine and terrestrial aquatic systems can lead to unbalanced (non-Redfield) nutrient abundances. A proxy for nutrient production is lipid fatty acids. Water and sediment samples were collected from Little Red River tributaries in Searcy County, Arkansas. Organics for pesticide analysis were extracted from the water samples. Fatty acids were extracted from sediments and underwent a combined transesterfication/derivitization process forming fatty acid methyl esters (FAMEs). FAMEs and dissolved organics were analyzed using GC-MS. Pesticide degradation products were found in several water samples. FAMEs were abundant at all sites. Future research will assess the relations between fatty acids, nucleic acids and black shale weathering in this region.