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23rd October 2014

Factoring Ecological Significance of Sources into Phosphorus Source Apportionment

Pie charts of changing ecological significance of sources

Models describing the relative contributions of phosphorus (P) from different sources to water bodies (source apportionment) are key tools in determining priorities for mitigation strategies within the River Basin Management Planning process under the Water Framework Directive (WFD). Previous source apportionment was simplistic because it was based on total P loads, even though not all P loading has the same ecological significance due to the form or timing of the loading. This project develops a descriptive methodology of how Total P loads provided by existing catchment models could be modified to take account of their impact on ecology. This modification works each modelled source (e.g. arable drainflow, urban runoff, grassland drainflow) through a sequential set of provided tables to adjust loads from Total P to bio-available P and then account for residence time and dilution potential. Data from the Tarland catchment is used to show a worked example of the method and the effect of accounting for ecological significance in the model.