Last week, Natural Resources Wales and Dŵr Cymru Welsh Water published SAGIS modelling on the sources of phosphorus pollution in the River Dee & Llyn Tegid Special Area of Conservation (SAC). While all rivers contain a natural input of phosphorus from decaying leaf litter etc., high levels are detrimental to river wildlife and current high levels are damaging the River Dee.
The source apportionment graphical information system (SAGIS) modelling results indicate that the Dee is discharging 122kg of phosphorus from the catchment daily. The model breaks down phosphorus sources into 45% from sewage treatment works, 24% from agriculture, 10% from storm overflows and 21% from other sources including septic tanks, urban run-off and industry. The full report can be found here.
The modelling is not perfect – it is based on a variety of assumptions and imperfect data. In particular, the type of phosphorous measured in SAGIS modelling is highly likely to underestimate the role of agriculture in phosphorus pollution. The figures should not, therefore, be taken as gospel but they do provide an important overview of sources.
At Welsh Dee Trust we are pleased that these draft outputs from the models have been released. They set an important direction and benchmark for work to stop and reverse the ongoing decline in the River Dee. At Welsh Dee Trust we are already working with farmers to reduce the impacts of agricultural pollution via our Water Wise Farming programme and training citizen science volunteers to help identify the road drains, septic tanks and industrial sources of pollution. We now ask that Dŵr Cymru look to significantly increase their investment in the sewage network within the Dee to rapidly reduce their contribution to the pollution of the river.