Relationships between benthic sediments and water column phosphorus in Illinois streams

Sediments can be important in regulating stream water P concentrations, and this has implications for establishing nutrient standards that have not been fully investigated. We evaluated abiotic and biotic processes to better understand the role of sediments in determining stream water dissolved P concentrations. Sediment and stream water samples were collected during low discharge from 105 streams across Illinois and analyzed for equilibrium P concentration at zero release or retention (EPC ₀), P sorption characteristics, stream water P concentration, and sediment particle size. In addition, four east-central Illinois streams were repeatedly sampled to examine temporal patterns in sediment P retention and biotic processing of P. Median dissolved reactive P (DRP) and total P concentrations across the state were 0.081 and 0.168 mg L _-1, respectively. Sediment EPC ⁰ concentrations were related to stream water DRP concentrations (r ^s = 0.75). Sediment silt+clay (and co-correlated organic matter) was related to sorbed P (r _s = -0.49) and the reactive sediment pool of P (r _s = 0.76). However, for most sites this pool was small given the coarse textures present (median silt+clay was 5.7%). Repeated sampling at the four intensive sites showed little variation in EPC ₀ values or alkaline phosphatase activity, suggesting overall stream conditions regulated the biotic processing. Biotic retention of P was 32% of short-term P removal. We conclude that sediments in Illinois streams are a reflection of and partially affected by stream water P concentrations through both abiotic and biotic processes. Sediments seem unlikely to alter annual stream P loads, but may affect concentrations at low discharge.