Monday, June 4, 2007 - 4:30 PM
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Influence of catchment bedrock geology on hydrology, chemistry, and ecosystem metabolism in forested headwater streams

Brian J. Roberts and Patrick J. Mulholland. Environmental Sciences Division, Oak Ridge National Laboratory, Bethel Valley Road, PO Box 2008, Oak Ridge, TN 37831-6036

Stream discharge and daily GPP and respiration rates have been measured continuously and baseflow chemistry has been measured weekly in Middle Sister Branch, a first-order forested stream in a shale catchment in eastern Tennessee since September 2005. Temporal patterns in each parameter were compared to longer records in Walker Branch, a nearby (~1 km) first-order forested stream draining a similar sized dolomite catchment. These streams have similar deciduous forests, orientations, light regime, shallow gradients, and streambed composition. Stream chemistry is different in the two streams with Middle Sister having more variable DIN (higher in summer and lower in autumn) and higher DON, P and DOC, consistent with results from a broader survey of 9 dolomite and 10 shale streams in the area. Middle Sister has a flashier hydrograph with higher peak flows following storms but quicker returns to baseflow conditions. Paired analyses of several storms show greater increases in ammonium and sulfate in Middle Sister suggesting differences in storm flowpaths and/or solute sources in these catchments. Temporal patterns in ecosystem metabolism are similar with Middle Sister having lower rates. These findings show that bedrock geology can be an important driver of both physico-chemical and biological processing of stream ecosystems.