Effects of surface and groundwater interactions on phosphorus transport within streambank sediments.
Understanding internal stream P transfers is important in controlling eutrophication. To determine the direction of groundwater and surface water interactions and evaluate P retention within streambank sediments, groundwater well pairs, about 5-m deep, were installed at three locations along a second-order, eutrophic stream in north-central Texas. Well cores were analyzed for P, and groundwater levels were monitored for about 2 yr. Water levels in wells furthest upstream always indicated a losing stream, while wells further downstream showed a gaining stream except during flow reversals with storm events and periods with reservoir backwater. Total-P from well cores ranged from 54 to 254 mg kg(-1) and was typically high near surface, decreased downward until redoximorphic features were encountered and then increased notably with depth to near or above surface concentrations. Very little extractable P occurred in sediments from the two upstream well sets; however, the set furthest downstream showed extractable P throughout with a high of 21 mg kg(-1) near the bottom. Repeated wetting-drying at sites A and B as noted by redoximorphic features may have shifted P into more stable sediment-bound forms. The decrease in extractable P at sites A and B compared to site C may be explained by conditions at C that were wetter and potentially anaerobic. Because the overall stream reach was more often losing than gaining, there appears to be a mass flow of P into streambank sediments. Streambank erosion may then transport this P downstream if not controlled.
Thompson
Carol A
CA
Department of Chemistry, Tarleton State University, Stephenville, TX 76402, USA.
McFarland
Anne M S
AM
D019015:Geologic Sediments / Q000032:analysis*; D055593:Geological Phenomena; D010758:Phosphorus / Q000032:analysis* / Q000737:chemistry; D045483:Rivers / Q000737:chemistry*; D013781:Texas; D014867:Water / Q000032:analysis*
D014867:Water; D010758:Phosphorus