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Research article - Peer-reviewed, 2012

Estimated trophic state effects and abatement costs in connection with improved urban sewage treatment in the Gulf of Riga

Bryhn, Andreas


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

Authors' information

Swedish University of Agricultural Sciences, Department of Aquatic Resources

Sustainable Development Goals

SDG6 Clean water
SDG14 Life below water
SDG11 Sustainable cities and communities

UKÄ Subject classification

Environmental Management
Oceanography, Hydrology, Water Resources
Other Biological Topics
Environmental Sciences

Publication Identifiers


URI (permanent link to this page)