Cross sector contributions to river pollution in England and Wales: Updating waterbody scale information to support policy delivery for the Water Framework Directive

Diffuse water pollution represents a major environmental issue for the European Union. Attempts to provide a coordinated approach to the management of the freshwater environment require appropriate tools for macro-scale spatial analysis to deliver the evidence base for informing targeted decision making and interventions. In this context, this paper reports the development of a new national multiple pollutant (nutrients and sediment)-source apportionment screening framework for England and Wales. SEPARATE (SEctor Pollutant AppoRtionment for the AquaTic Environment) includes emissions to the aquatic environment from both diffuse (agriculture, urban, river channel banks, atmospheric) and point (sewage treatment works (STWs), septic tanks, combined sewer overflows (CSOs), storm tanks) sources and summarises the source apportionment on the basis of Water Framework Directive cycle 2 waterbodies. National scale source proportions (with waterbody ranges) for total nitrogen (TN) were estimated to be in the order; agriculture (81%, 1-100%) > STWs (14%, 0-95%) > CSOs (1.5%, 0-73%) > direct atmospheric deposition (1.3%, 0-93%) >diffuse urban and storm tanks (both 1%, 0-80% and 0-93%) >septic tanks (0.2%, 0-30%) >river channel banks (∼0%, 0-1%). The corresponding estimates for total phosphorus (TP) were; STWs (47%, 0-100%) > agriculture (31%, 0-100%) > CSOs (9%, 0-94%) > storm tanks (6%, 0-100%) > diffuse urban/septic tanks/river channel banks (all 2%, 0-100%, 0-70%, 0-71%) > direct atmospheric deposition (1%, 0-65%). For sediment, the estimates were in the order; agriculture (72%, 0-100%) > river channel banks (22%, 0-96%) > diffuse urban (5%, 0-100%) > STWs (1%, 0-91%). Without the inclusion of groundwater sources, agricultural contributions dominate water pollution by TN in 93% (130,384 km2) of waterbodies across England Wales, compared to 58% (68,434 km2) in the case of TP and 76% (104,434 km2) for sediment. In combination, agricultural contributions of all three of these pollutants are dominant in 53% (63,030 km2) of waterbodies.