Source apportionment of nutrient contributions to rivers in England and Wales modelled with SAGIS

This dataset has been modelled with The Source Apportionment-GIS (SAGIS) using data from the period spanning from 2006 to 2009. Input datasets include: river network outline, water body boundary, hydrology and river monitoring data, rainfall, land use and agricultural data, on-site wastewater treatment system, sewage treatment works, combined sewer overflows and storm tank locations, soil erosion, highway runoff and pollution inventory industrial discharges to river and sewer including extensive sewage treatment works data. Loads are converted to concentrations in river waters using the SIMulation of CATchments (SIMCAT) water quality model, which is incorporated within SAGIS, so that the contribution to in-stream concentrations from individual sources can be quantified. Diffuse sources of nutrient pollution are incorporated into SAGIS from the Phosphorus and Sediment Yield Characterisation In Catchments (PSYCHIC) model (developed by a consortium of academic and government organisations led by ADAS Water Quality). SAGIS models are not time based and do not show seasonal variation; river flow can vary according to seasonal changes which would have an impact on results. The model will also always be a simplified version of reality and so must be used as an advisory tool and not as the sole basis of decisions. Data is often subject to change and so the models require regular updates. Livestock and arable inputs have been calculated from the ADAS models PSYCHIC and NEAPN and have been shown to overestimate inputs in some areas. There is also a related issue, of changing crop types and land use.