How effective are reedbeds, ponds, restored and constructed wetlands at retaining nitrogen, phosphorus and suspended sediment from agricultural pollution in England?

A high priority topic within the Department for Environment, Food and Rural Affairs (DEFRA) water quality programme is the mitigation of diffuse rural pollution from agriculture. Wetlands are often cited as being effective at reducing nutrient and sediment loadings to receiving waters. However, the research in this area is inconsistent, and whilst most studies have shown that both natural and constructed wetlands retain nutrients and sediments, others have shown that they have little effect, or even increase nutrient and sediment loads to receiving water bodies. DEFRA has commissioned a systematic review on the use of wetlands to mitigate N, P and SS inputs from agriculture to receiving freshwater in England. The review will encompass a comprehensive literature search on all available material on the subject, both published and unpublished within the British Isles. Specific inclusion criteria will be adhered to and a formal assessment of the quality and reliability of the studies will be undertaken. The data will then be extracted and a data synthesis undertaken. The review will inform an evidence-based policy that can be implemented by stakeholders.