AbstractsEarth & Environmental Science

Nutrient inflows from anthropogenic sources into water systems are causing eutrophication, algal blooms and trophic changes in Swedish lakes and seas. The European water framework directive was implemented to regulate member countries' policies to achieve a good status in surface waters. Reduction fishing has shown to be an effective lake restoration tool involving removal of large quantities of planktivorous fish, decreasing the internal nutrient loads and recovering the lake status. The Administrative board of Östergötland (Länsstyrelsen Östergötland) started this project with the aims to find out how to dispose of the fish from reduction fishing projects in a sustainable way in the county of Östergötland. With analysis of secondary lake data, the study also aims to highlight the ecological and chemical status in five of the county's most eutrophic lakes: Asplången, Värnässjön, Svinstadsjön, Nimmern and Hällerstadsjön. The amount of predicted catch during a reduction project, for each lake with the corresponding amount of phosphorus (P) and nitrogen (N) removal, was calculated based on lake area and reduction fishing guidelines. To find out the prospects and possibilities fora sustainable catch disposal, literature review, interviews and communication with possible stakeholders in the area were conducted and analysed in a SWOT-analysis (Strengths, Weaknesses, Opportunities, Threats) as wellas for three sustainability criteria based on the Swedish waste regulation. The results showed that the ecological status is ranging from bad to moderate in the five studied lakes and that approximately 162 - 218 tonnes of fishcould be removed which corresponds to a reduction of P by ca. 1.1 - 1.5 tonnes and N by ca. 4.4 - 5.9. Four possible disposal methods were determined: the use of bream and roach as food for humans, for animal feed, for production of biogas and waste disposal by incineration. Roach and bream for human consumption showed to be a possible option despite a huge resistance in acceptance of roach and bream as edible fishes. Fish as feed was also possible if used as bait for fishing. Biogas production from fish worked well at the local biogas plant as long as the fish was prepared in the right way. Incineration could work as an easy way to dispose off the fish. The SWOT-analysis showed most strengths and possibilities for the biogas option, whereas the food alternative had more weaknesses and threats. However, due to waste management regulations, the use of roach and bream as food or animal feed were the more sustainable options.