Abstract
AbstractMitigation of diffuse water pollution from agriculture is of concern in the United Kingdom, so that freshwater quality can be improved in line with environmental objectives. Targeted on‐farm mitigation is necessary for controlling sources of pollution to rivers; a positive impact must also be delivered at the subcatchment and catchment scales before good ecological status can be achieved. A farm on the River Sem in the Hampshire Avon Demonstration Test Catchment was selected for monitoring due to its degraded farmyard, track, and drainage ditch, which was targeted by the Demonstration Test Catchment programme for improvement using a treatment train of interventions. The river was monitored before and after, upstream and downstream, of the potential sources of pollution and subsequent mitigation, both locally at farm scale, and downstream at the subcatchment scale. Sediment was obtained from the riverbed using a conventional disturbance technique, and source samples were collected from across the subcatchment. Samples were analysed for geochemistry, mineral magnetism, and environmental radionuclide activity using the <63‐μm fraction, before sediment source fingerprinting was conducted to apportion sources. Source tracing revealed that, although the degraded farm track was experiencing channelized flow and erosion in the pre‐mitigation period, it was not a major sediment source even at farm scale. Repeat source apportionment during the pre‐ and post‐mitigation periods showed that the targeted treatment train did not result in statistically significant decreases in predicted contributions from the farm track sources at either scale. Sediment sources must be determined at a range of spatial scales to support effective mitigation.
Highlights
Mitigation of diffuse water pollution from agriculture (DWPA) is of primary concern in the UK, due to policy objectives to improve water quality and requirements to achieve ‘good ecological status’ of freshwaters under the EU Water Framework Directive (WFD; European Parliament, 2000; 2000/60/EC)
The findings of this study underscore that it is vital that the major sources of sediment are identified at a variety of spatial scales within any given landscape prioritised for mitigation of DWPA, so that interventions can be targeted correctly
Failure to consider sediment sources and process domains across a range of spatial scales, from individual farms to landscape scale, is likely to reduce the efficacy of the on-farm interventions, especially at those scales currently used for water quality compliance reporting
Summary
Mitigation of diffuse water pollution from agriculture (DWPA) is of primary concern in the UK, due to policy objectives to improve water quality and requirements to achieve ‘good ecological status’ of freshwaters under the EU Water Framework Directive (WFD; European Parliament, 2000; 2000/60/EC). Farm-scale improvements to water quality through targeted mitigation of DWPA need to deliver a positive impact at sub-catchment and catchment scales before good ecological status can be achieved at the compliance reporting scales (e.g. WFD waterbodies) used for current policy delivery and assessment. It is important, that on-farm mitigation is effective enough to show an impact further downstream. Issues include targeting the most important on-farm pollutant sources and delivery pathways, the density of the on-farm measures across different landscape scales, the contribution of agricultural inputs to the water quality problem in the context of non-agricultural sources, including urban areas and domestic septic tanks, changing hydrological/biogeochemical process domains, and the maintenance of measures following implementation
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