Projected impacts of increased uptake of source control mitigation measures on agricultural diffuse pollution emissions to water and air

A multi-pollutant modelling framework for England and Wales is described. This includes emissions of nitrate, phosphorus and sediment to water and ammonia, methane and nitrous oxide to air, and has been used to characterise baseline (no uptake of on-farm measures) and business-as-usual (BAU) annual pollutant losses, comparing these with the loss under a range of new policies aimed at increasing the uptake of relevant source control measures to 95% across England and Wales. Model outputs, including uncertainty ranges, evaluated using national water and air quality data layers have been summarised at both farm (Robust Farm Type) and water management catchment (WMC) scale. Nationally, across all farm types, the median annual reductions in pollutant losses under the new scenario, relative to BAU in 2010, were predicted to range between 9 and 16% for nitrate, 13-37% for phosphorus, 12-21% for sediment, 2-57% for methane and 10-17% for nitrous oxide. For ammonia, the range was −2-28%, indicating the potential for pollution swapping and an increase in ammonia emissions under scenarios designed to reduce nitrogen flux to waters. Increased uptake of pollution source control measures would result in a wide range of annual total (capital and operational) costs (per farm) for the major farm types, with median estimates ranging from £635 yr−1 (Less Favourable Areas (LFA) with grazing livestock) to £15,492 yr−1 (Cereals) in Nitrate Vulnerable Zone (NVZ) areas, compared with a range of £23 yr−1 to £13,484 yr−1 for the same respective farm types in non-NVZ areas. The estimated median annual load reductions for all WMCs relative to BAU, were predicted to be 16% for nitrate, 20% for phosphorus, 16% for sediment, 16% for ammonia, 15% for methane and 18% for nitrous oxide. These predictions suggest that almost perfect (95% uptake) implementation of source control measures will not deliver substantial improvements in pollutant emissions.