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Presented at the NABS Annual meeting, Anchorage, Alaska, 2006
in Special
Partitioning the flood pulse: The biogeochemistry of floodwaters in a restored free-flowing river-floodplain system
D.S. Ahearn1, C.A. Jeffres2, J.F. Mount3, and R.A. Dahlgren1.1Department of Land, Air, and Water Resources, University of California, Davis, California 95616, 2Center for Watershed Sciences, University of California, Davis, California 95616, 3Department of Geology, University of California, Davis, California 95616
Floodwaters traversing a 36 ha restored floodplain in central California were monitored for suspended sediment, nutrients, dissolved organic carbon (DOC), and chlorophyll-a (Chl-a) from December 2004 to June 2005. The floodplain was an annual sink for all measured constituents. However, closer analysis revealed that some small flooding events caused net DOC and Chl-a export from the floodplain. Partitioning of the flood pulse revealed three physically and chemically distinct stages: the flushing phase, transport phase, and draining phase. The flushing phase was a brief period of net export on the rising limb of the flood. The transport phase dominated the annual flux balance of the system and was marked by net retention of all the measured constituents on the floodplain. The draining phase was characterized by net export of DOC and Chl-a. The fact that small floods had brief transport phases helps explain why smaller floods tended to cause net export, rather than retention, of measured constituents on the floodplain. We provide a conceptual model of the flood pulse phases which includes and broadens the model proposed by Tockner et al. (1999). Finally, we propose the notion of “floodplain proportional flooding” for optimizing diverse food resource export from restored floodplain systems.
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