Can field wetlands trap eroding agricultural soil?


Dr Clare Deasy
Senior Research Associate
Lancaster Environment Centre, Lancaster University

A shallow field wetland located in a field corner on a mixed agricultural farm in Cumbria, UK, showing the wetland collecting surface runoff eroding soil from agricultural fields during a storm event.

Field wetlands are small constructed wetlands designed to trap eroded soil and associated pollutants from diffuse sources including field surface runoff and runoff from drains and ditches. Data from ten UK trial field wetlands created on unproductive agricultural land, in field corners and in buffer strips, indicate that field wetlands can be very effective at sediment and nutrient trapping.  Up to 26 tonnes of sediment have been stored in individual field wetlands annually, equating to 0.5 tonnes ha-1 yr-1, with wetland soils trapping total phosphorus at a rate of up to 1kg TP ha-1yr-1 and total nitrogen at a rate of up to 2kg TN ha-1yr-1.

A shallow field wetland located in a field corner on a mixed agricultural farm in Cumbria, UK, showing the sediment deposit in the wetland the following summer.

Field wetlands are also designed to be wildlife habitats, and can help store floodwater. They are easy and cheap to construct using on-farm machinery or by bringing in contractors, and on-going maintenance and farm-scale costs are likely to be minimal. The project team at Lancaster University have recently published policy guidance on using field wetlands, with a construction guidance document about to be released. A series of field wetland case studies and further information are now available on the project website.

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