Water policy effectiveness: 30Â Years of change in the hypernutrified Colne estuary, England

Wastewater discharges and agricultural run-off have caused nutrient enrichment leading to eutrophication, in receiving waters worldwide. Analysis of a 30 year data set (1981-2010) for the Colne estuary, a hypernutrified estuary in the south-east of England, revealed significant reductions in nutrient concentrations in freshwater inputs and along the estuarine gradient linked to management actions. DIN concentrations decreased, mainly as a result of reduced ammonia outputs from Colchester STW and reduced nitrate loads from the catchment. Declines in phosphate concentrations occurred due to improved STW processes. There were significant declines in phytoplankton chlorophyll a over the period. Long-term trajectories of nutrient decreases were also strongly influenced by interannual patterns of rainfall and climatic signals (winter NAO). Standardised winter DIN concentrations in the Colne estuary significantly exceed the Water Framework Directive good status target, but the estuary shows no symptoms of eutrophication.