Sediment-phosphorus relationships in three northcentral Oklahoma streams

Sediment characteristics related to their potential for P uptake and buffering capacity were examined in three adjacent Oklahoma streams in order to determine if stream sediments were the dominant controllers of water column P and if benthic sediments were capable of buffering growing P loads to these systems. Sediment and water samples were collected from Council Creek, Feather Creek and Little Stillwater Creek in northcentral Oklahoma. Particle size distribution, equilibrium phosphate concentration (EPC0), phosphorus sorption index (PSI), and exchangeable-P were measured for a single date for benthic sediments from each site. There were no detectable differences in particle size composition; however, sediment attributes related to P varied significantly among sites. Sediments from Little Stillwater Creek had higher exchangeable P content and EPC0 relative to the other two sites. There were no consistent relationships between exchangeable P and sediment or water characteristics, while EPC0 was significantly correlated with percent silt. Sediment and water phosphate pools were in equilibrium at only one site. At the other two sites, either the sediment/water balance was temporarily in disequilibrium, or sediments were not the major determinant of water column P. In contrast to the other sediment metrics, PSI did not vary among sites. Total sorption potential was attributed to both abiotic and biotic uptake, with biotic removal becoming increasingly important for sediments with high PSI values. Disequilibrium between sediment and water column P and the relative importance of biotic sorption to PSI measurements suggest that factors other than, or in addition to, physical and geochemical processes associated with benthic sediments, are important in controlling streamwater P concentration and retention.