The Source Apportionment-GIS (SAGIS) modelling framework was developed through UWKIR research project WW02: Chemical Source Apportionment under the WFD (UKWIR, 2012) with support from the Environment Agency. The primary objective of this research was to develop a common modelling framework as the basis for deriving robust estimates of pollution source contributions that would be used to support both water company business plans and the EA River Basin Planning process.

The SAGIS tool quantifies the loads of pollutants to surface waters in the UK from 12 point and diffuse sources including wastewater treatment works discharges, intermittent discharges from sewerage and runoff, agriculture, soil erosion, mine water drainage, septic tanks and industrial inputs (UKWIR project WW02). Loads are converted to concentrations 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).

PSYCHIC is a process‐based model of phosphorus and suspended sediment mobilisation in land runoff and subsequent delivery to watercourses. Modelled transfer pathways include release of desorbable soil phosphorus, detachment of suspended solids and associated particulate phosphorus, incidental losses from manure and fertiliser applications, losses from hard standings, the transport of all the above to watercourses in under‐drainage (where present) and via surface pathways, and losses of dissolved phosphorus from point sources.

The maps below show the baseline export of total phosphorus from manure-based sources across the Tamar catchment predicted by the PYCHIC model (left) and the modelled concentrations of Soluble Reactive Phosphate in sub-catchments of the Tamar and their sources according to the SAGIS modelling tool (right).
 
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