Tuesday, May 27, 2008
324

Seasonal variation of primary production in streams in the Florida parishes of Louisiana

Jonathan L. West and William E. Kelso. Renewable Natural Resources, Louisiana State University, Baton Rouge, LA 70803

Primary production (PP) in Louisiana streams may be limited by lack of light or suitable substrate, or enhanced by nutrients.  We studied PP via diel oxygen curves and evaluated nutrient limitation in two sandy, nutrient-rich streams through four seasons in 2007.  One site, West Fork of Thompson Creek (WFT), had an unconstrained channel with a wide floodplain and relatively little shading by trees.  High discharges tended to disturb stream sediment and scour the stream of algae and the floodplain of vegetation.  In contrast, Tchefuncte River (TCH) had an incised channel with greater shading by trees, and high discharge events had less of an effect on the stream or floodplain.  PP varied seasonally at WFT, with highest rates during summer after a long period of low flow.  Lowest rates occurred in winter when temperatures were relatively low and frequent high discharges disturbed sediments and scoured algae.  Nitrogen (as nitrate) tended to limit algal growth in WFT.  We did not observe much variation in PP or nutrient limitation in TCH as overstory shading may be the most limiting factor for algal growth in this stream.  Our results suggest that hydrologic characteristics of these streams may prevent processing of excess nutrients by algae.

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