Tuesday, June 5, 2007 - 11:45 AM
134

Effects of Suspended Sediments on Downstream Biogeochemistry following Dam Removal

J. Adam Riggsbee1, Jason P. Julian2, Martin W. Doyle2, and Robert G. Wetzel1. (1) Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, NC 27599-7431, (2) Department of Geography, University of North Carolina, 205 Saunders Hall, CB# 3220, Chapel Hill, NC 27599-3220

We studied the effects of high suspended sediment loads on river biogeochemistry following dam removal using a longitudinal water sampling network during a dam removal event on the Deep River, North Carolina.  Suspended sediment concentrations following dam removal reached ~325 mg L-1, comparable to concentrations carried during bankfull floods.  Concentrations of carbon, nitrogen, phosphorus and iron were measured at one location upstream and three locations downstream of the reservoir.  These data were coupled with discharge measurements to quantify water and biogeochemical budgets, and to quantify the transport and attenuation of sediment and solute pulses.  In complementary laboratory experiments, sediment solutions (~325 mg L-1) were exposed to simulated solar radiation, equivalent to a summer day at 36o N latitude.  We found that sediment suspensions in the presence of solar radiation were significant sources of C (1.43 + 0.66 mg C L-1 d-1) and DON (0.02 + 0.04 mg N L-1 d-1), but not DIN or SRP.  Finally, sediments lowered river water Fed concentrations immediately (~ 24%) and progressively (~40-90%) in both light and dark treatments.  Field and laboratory data are compared to determine if photochemical mechanisms enrich the water column with DOC and DON during dam removal. 

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