Method analysis of laboratory measures of stream sediment and water phosphorus equilibrium

Elevated phosphorus concentrations in aquatic ecosystems of northwest Arkansas prompted an investigation of the effects of sample preparation and extraction methods on laboratory measures of sediment-phosphorus interactions. Two streams of contrasting phosphorus (P) concentrations were selected to determine the effect of using a CaCl2 solution instead of filtered stream water, refrigerated or dried sediments instead of fresh wet sediments, and vortexing the suspensions instead of shaking them. Sediment equilibrium P concentration (EPC0) and P buffering capacity (K) were used to determine differences in extraction methods. EPC0 and K from extractions using fresh sediments and a CaCl2 solution matching the electrical conductivity of the stream water were not significantly different from extractions using fresh sediments and filtered stream water. However, using dried sediments instead of fresh, wet sediments in the extraction procedure affected EPC0 and K estimation. In the P-enriched system, sediment extractions using refrigerated sediments or vortex mixing of the sediment-slurry suspension produced EPC0 and K estimates that were significantly different than estimates from fresh, wet sediment and filtered stream-water extractions. Overall, method analysis of laboratory measures of stream sediment and water P equilibrium suggested that in low-P-concentration streams, estimates varied little whereas in high-P streams the method of extraction was more important