Abstract

Environmental conflicts of interest are important to account for when environmental policies are designed. This paper explores the quantitative connection between urban wastewater treatment, coastal eutrophication, and fish biomass in the mesotrophic Gulf of Riga (northern Europe). The probable effect on the water quality from one clearly defined abatement measure, improved urban sewage treatment, has been studied. The implementation cost and the likely effect on total fish biomass also have been assessed. Computer simulations by using the previously published model CoastMab suggested that good water quality according to the European Union (EU Marine) Strategy Framework Directive could be achieved if urban sewage treatment would be upgraded to Nordic and German standards, and not only around the Gulf of Riga but also in the whole Baltic Sea drainage basin. The Secchi depth would double according to these simulations, whereas total phosphorus and summer chlorophyll concentrations would decrease by 54% and 53%, respectively. The total fish biomass should be expected to decrease by approximately 42% if good water quality (as defined in EU directives) should be achieved. However, changes in total fish biomass also could be offset by changes in other important determinants, such as climate-related variables or fishing pressure. The study estimated that it could take approximately 20-40years after abatement action for the trophic state in the Gulf to stabilise again. Upgrading urban sewage treatment to this extent would cost 468-1,118million Euro per year. Treatment could have substantial positive effects on the water quality of the Gulf but could also have adverse side effects on the total fish biomass.

Published in

Journal of Environmental Engineering
2012, volume: 138, number: 6, pages: 663–672

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