Nutrients and Eutrophication in the Taw Estuary

I. Increased inputs of nutrients to estuaries can lead to undesirable effects associated with eutrophication,including algal blooms, changes in species composition and bottom anoxia. Several estuaries and coastal areasaround the UK have increased nitrogen (N) and phosphorus (P) concentrations, elevated concentrations ofchlorophyll a and changes in algal community composition and abundance. This paper reviews the pressures thatlead to high nutrient concentrations in estuaries and considers the likely effectiveness of current and proposedregulatory actions.2. The main sources of nutrients to estuaries are river runoff, sewage discharges, atmospheric inputs andpossibly submarine groundwaler discharges, although little is known about the latter. Significant reductions in Nand P inputs have been realized following application of the EU's Urban Waste Water Treatment Directive.Atmospheric NO, and NH, emissions have also decreased and are expected to decrease further in the next decadeas implementation of existing legislation continues, and new controls are introduced for activities such asshipping.3. Agricultural inputs reach estuaries principally through diffuse sources, either in surface water (and in someareas possibly groundwater) or, for N, via the atmosphere. Over 10 years ago the Nitrates Directive wasintroduced to tackle the problem of N discharges from agriculture but little change in N loads to estuaries hasbeen recorded.4. To meet the aims of the EU Water Framework Directive, for at least 'good' ecological status, more rigorousapplication and implementation of the Nitrates Directive, together with changes in the Common AgriculturePolicy and farming practice are likely to be needed. Even then, the slow response of the natural environment tochange and the inherent variability of estuaries means that their responses may not be as predicted. Research isneeded into the relationship between policy drivers and environmental responses to ensure actions taken willachieve the planned results.Copyright© 2008 John Wiley & Sons, Ltd.Received 9 May 2007; Revised 23 January 2008; Accepted 2 March 2008