Temperature and nitrogen effects on phosphorus uptake by agricultural stream-bed sediments

Climate change will likely increase the growing season, temperatures, and ratio of nitrogen (N) to phosphorus (P) loss from land to water. However, it is unknown how these factors influence P concentrations in streams. We sought to evaluate differences in biotic and abiotic processes affecting stream sediment P dynamics under different temperature and N-enrichment regimes. Three sediments of varying P composition and sorption characteristics were placed into a fluvarium. Synthetic runoff water, with or without added N, was added to the flume's reservoir, and the solution was maintained at 19 or 26°C. Water and sediment samples were taken with time since runoff was introduced. The rate and magnitude of P uptake by sediment was greater at 19°C compared with 26°C, and also when N was added compared with no N added. Analysis of sediment samples indicated that P uptake via abiotic processes was greater at 19 than at 26°C. The addition of N stimulated P uptake by the microbial biomass at 19°C, but microbial uptake was potentially inhibited at 26°C. Because microbial biomass is a temporary store of P, these data suggest that more P may be available with increasing temperatures during the growing season, especially under baseflow, implying that strategies to mitigate P losses from land to water should be strengthened to prevent potential water quality impairment.