Impacts of agricultural land use on streamwater and sediment phosphorus concentrations: implications for phosphorus-cycling in lowland rivers.

Abstract

Research over the last decade has identified agricultural land-use practices of highest risk for P-losses at the field and farm scales, and the forms in which P is exported (Withers and Lord, 2002). However, the impacts on streamwater quality and ecology are less well characterised at the catchment scale (Jarvie et al., 2006). In this study, we tested the hypothesis that differences in agricultural land use have a significant impact on streamwater and bed sediment P concentrations and the ability of bed sediments to act as sources/sinks of soluble reactive P (SRP). Three catchments systems were monitored in lowland England and Wales (Wye, Avon and Loddington), characteristic of selected livestock and farming systems with variable P-loss risk (Table 1). For each catchment system, one stream drained a very low intensity agriculture (providing a 'control'), while the other stream(s) drained high-risk agriculture. Streamwater nutrient chemistry was monitored on a weekly basis over two years. Surface fine (<2mm) bed sediments were sampled in spring and late summer and analysed for total P and total Fe concentrations and Equilibrium Phosphorus Concentrations (EPC₀) (Jarvie et al., 2005). Diffusive Equilibrium in Thin films (DET) gel probes (Jarvie et al., in press) were deployed at Loddington for in-situ assessment of sediment-water SRP diffusion gradients and fluxes.