Sediment-phosphorus relationships in three northcentral Oklahoma streams

Sediment characteristics related to their potential for P uptake and buffer ing capacity were examined in three adjacent Oklahoma streams in order to d etermine if stream sediments were the dominant controllers of water column P and if benthic sediments were capable of buffering growing P loads to the se systems. Sediment and water samples were collected from Council Creek, F eather 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 fo r benthic sediments from each site. There were no detectable differences in particle size composition; however; sediment attributes related to P varie d significantly among sites. Sediments from Little Stillwater Creek had hig her exchangeable P content and EPC0 relative to the other two sites. There were no consistent relationships between exchangeable P and sediment or wat er characteristics, while EPC0 was significantly correlated with percent si lt. 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 co lumn P. In contrast to the other sediment metrics, PSI did not vary among s ites. Total sorption potential was attributed to both abiotic and biotic up take, with biotic removal becoming increasingly important for sediments wit h high PSI values. Disequilibrium between sediment and water column P and t he relative importance of biotic sorption to PSI measurements suggest that factors other than, or in addition to, physical and geochemical processes a ssociated with benthic sediments, are important in controlling streamwater P concentration and retention.