SPATIAL AND TEMPORAL VARIATIONS IN SEDIMENT ORGANIC MATTER (SOM) FROM A STREAM DRAINING MIXED-USE LANDSCAPES

Soil organic matter (SOM), the accumulated, decaying debris of biota living on or in the soil, represents the largest of the active terrestrial C pools, holding about 1500 Pg C to a depth of 1 m. In aquatic ecosystems, SOM is a storehouse of inorganic nutrients which, after mineralization, are released to the stream and used by planktonic and benthic microorganisms. Here we present the results of a study designed to elucidate the controls on the spatial and temporal variations of the SOM distribution along the Clear Fork River, which drains a mixed urban-agricultural landscape in north-central Ohio. Fluvial bed sediments were sampled monthly (between March and November) in eight stations along the river. Organic matter (OM) and carbonate content were determined by loss-on-ignition (LOI). Sediments from all sampling stations were analyzed in triplicate to account for OM and carbonate variations within the sample and provide a measure of precision (always below 1.5%; average 0.4%). Since OM content and C solubility is dependent on sediment grain size, textural analysis was also performed in all samples. Preliminary results show OM content varying between 14 and 86 g kg^-1, with highest values being observed during spring, and lower values during summer. Sediments from stations where the stream flow is high generally presented lower OM concentration. In addition, stations located within urban landscapes presented higher OM concentrations than those located within agricultural land.