Dissolved organic carbon quality and distribution within the sediments of a stream-lake-stream system

J. Nielsen, L. Jeffs, and M.A. Baker. Department of Biology, Utah State University, Logan, UT 84322

Dissolved organic carbon (DOC) is an important substrate for microbial metabolism in aquatic ecosystems. In snowmelt-dominated systems DOC is flushed from the catchment soils and sediments during spring runoff. We collected 12-hour daily composite samples for DOC in stream water above and below a lake from May to October 2002 in the Sawtooth Mountains, ID. To determine the variability of different sediment types as potential sources of DOC, we extracted DOC, measured DOC bioavailability, and estimated DOC quality as specific ultra violet absorbance (SUVA) value. DOC increased approximately 8 mg C/L over background in both stream reaches during snowmelt. The percent of OM in sediments ranged from 1 percent in sediments lateral to the streams and 42 percent in stream benthic sediments. DOC, SUVA values, and bioavailability varied among sediment types. Benthic (high moisture) sediments had higher percentages of OM and higher amounts of extracted organic carbon than surface (low moisture) sediments. However, DOC in surface sediments tended to be more bioavailable than DOC in benthic sediments. Though no spatial patterns were evident among sediment types, data suggest that DOC transport may alter organic carbon bioavailability.