Eutrophication in the River Itchen – Phosphate Modelling Evidence to Enable Permit Revisions

Posted: Wednesday 31st December 2014

WRc the Innovation consultancy in the Water, Waste and Gas sectors has been working with the Environment Agency to provide modelling evidence to enable permit changes for managing and reducing phosphate loads entering chalk streams in the Upper Itchen catchment. This area is designated a Special Area of Conservation (SAC) and as such is protected under the European Habitats Directive.

The source of the River Itchen is of excellent quality and provides great habitats for insects, fish, birds and otters; yet there have been high levels of phosphate recorded along the length of the river and this can cause eutrophication. The Agency called on WRc for catchment management modelling advice as they studied the interaction of river flows and water quality with local stakeholders - fish farms, sewage undertakers, watercress farms, farmers and other organisations.

WRc used the Agency’s river water quality permit setting model SIMCAT (Simulated Catchments) to show how river flows and phosphate inputs from different sources combine and affect the phosphate levels in the River Itchen catchment. The Agency used this evidence during 2013/14 to engage with stakeholders and agree revisions to discharge permits for fish farms and watercress farms in the upper catchment to reduce the levels of phosphate discharged to the Itchen. The watercress farms are aiming to comply with these new permits in 2016, while actions are on-going to reduce loadings from other agriculture sectors in the catchment.

Hampshire grown watercress and trout can now be produced in a more sustainable way as the Agency plans to revise permits for 14 watercress and fish farms to reduce the input of phosphate along the sensitive waters of the River Itchen.

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