Phosphorus dynamics in groundwater-fed rivers

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Reducing diffuse nutrient pollution is a prime focus of measures to improve the environmental status of UK rivers. In groundwater-fed rivers, processes operating in the hyporheic zone (HZ) and its interchange with surface waters (SW) are key drivers of the ecological health of the river. The HZ is the subsurface region beneath, or adjacent to, a SW body where mixing occurs with groundwater (GW). This zone is hydrologically, geochemically and microbiologically complex. Large redox-driven concentration gradients exist across the sediment-water interface. The resulting potential for complete consumption of dissolved oxygen in hyporheic flowpaths 10-100 cm into the streambed creates areas where anaerobic microorganisms dominate microbial activity, which in turn control the bioavailability of redox-sensitive elements such as nitrogen (N) and, indirectly, phosphorus (P). The retention/release of P through interaction between HZ flows and in-river (SW) processes may be particularly important because elevated P concentrations have been linked to increased rates of plant growth, changes in species composition and proliferation of planktonic and epiphytic and epibenthic algae in rivers. Such rivers often fail to meet the standards of the EU Water Framework Directive necessitating the introduction of expensive mitigation measures. These measures can only succeed if we understand the processes controlling the ecological health of the river. This project seeks to unravel these controls in relation to P dynamics in groundwater-fed rivers.The focus in on understanding of the temporal variation in nutrient processes in groundwater-fed rivers.