Stream bank Management, Retention and Transport of Phosphorus (SMART-P)

Reducing losses of phosphorus and sediments from agricultural land to waters is a crucial goal in the process of restoring and maintaining good ecological status in streams worldwide. Vegetated buffer strips (VBS) interposed between streams and crop, or pasture land are set to be a rapidly increasing phenomenon in managing transport of diffuse pollutants and are positively legislated for in the UK, Europe and USA. However, VBS need to be evaluated in terms of efficacy and risks and there are indications that this increasingly commonly adopted land management tool is inefficient at P retention, especially dissolved forms. Any resulting P leaching may affect compliance with Water Framework Directive stream P targets, but also any P accumulation in riparian soils has implications for any channel restoration and management measures affecting bank erosion. This studentship therefore aims to address the knowledge gap of P cycling and biogeochemistry under soil conditions specific to VBS. VBS pose a situation of rapid land use change in critical landscape zones at the interface between soils and waters. Previous exploratory investigations by the project team have suggested that VBS establishment brings changes in the pools of P leading to greater P release into solution and that this may be related to changes in biological communities as buffers develop. The studentship tests the hypothesis that that an increase in P solubility from VBS soils occurs due to enhanced cycling of soil P forms associated with the changes in biological communities as buffers establish. Alternatively, we will explore a more geochemical solubility process whereby leaching results from soils becoming progressively saturated with P as the buffer traps eroded sediments loaded with particulate P. The studentship will assess these mechanisms using an integrated biogeochemical approach to couple P cycling through terrestrial (soil - plant - microbial) to aquatic ecosystems (losses of P to stream waters). It is becoming apparent that pools of P (especially organic forms) thought of previously as refractory are actually rendered labile by biological processing. It may only take a small increase in the size of the labile P pool in relation to total soil P in typical agricultural systems to induce a large increase in P leaching and in effects on sensitive ecosystems of receiving surface waters. An improved understanding of cycling between inorganic and organic P forms will be a key novelty of the work in terms of understanding soil P accessibility and storage. The study will comprise a number of complimentary aspects of training to achieve the following outcomes: (i) development of the student's biogeochemical understanding of the problems of P management in buffer strips in realistic scenarios, (ii) training in catchment soil and water studies and of up-to-date soil biogeochemical analyses culminating in the provision of analytical tools to assess P cycling and (iii) to inform management of VBS for better efficiency of P use in agriculture. Four aspects will form the structure of the studentship over the 3 years: (1) Evaluation of current literature and data on water quality in relation to catchments with buffer strip management. (2) Field survey and establishment of field plots to understand the transitions in soil P biogeochemistry as cultivated land changes to VBS. (3) Development of soil biogeochemical indicators of P cycling including novel combinations of geochemical and microbiological characterisation. (4) Assessment of simple VBS management strategies aiming to encourage P retention and potential P recycling through reincorporating P enriched biomass back to fields.