Interstitial Dissolved Organic Carbon in Sediments of a Southern Appalachian Headwater Stream

This study had two objectives: (1) to compare seasonal and spatial patterns of water-column dissolved organic carbon (DOC) and sediment interstitial DOC (IDOC) concentrations at a headwater spring seep, and (2) to explore interactions between sediment organic matter content, benthic bacterial biomass and production, water column DOC concentration, and sediment IDOC concentration and composition (high versus low molecular weight components). For the first objective, sediment organic matter content, IDOC concentration (sampled from small wells by dialysis or by pipet), water column DOC concentration, and benthic bacterial biomass were measured at a spring seep in Coweeta Hydrologic Laboratory, Macon Co., North Carolina USA, for two years. For the second objective, organic matter content was increased or decreased in experimental sediments. The same variables listed above were measured within three weeks of sediment manipulation and again after five and a half months. Benthic bacterial production was measured one week after sediment manipulation. Results indicate benthic organic matter is a source of IDOC, the concentration of which depends on sediment organic matter content, the relative proportion of high and low molecular weight IDOC compounds, and the exchange of interstitial and water column DOC. High molecular weight IDOC (>50,000) accumulates in sediments in proportion to sediment organic matter content. Low molecular weight IDOC (<50,000) concentrations are lower than high molecular weight IDOC concentrations and are independent of sediment organic matter content. However, low molecular weight IDOC concentrations are generally greater than water column total DOC concentrations. Low molecular weight IDOC concentrations are greater during the dormant season than during the growing season.