Development of short and long-term management options for bergelenput to avoid fish kills caused by algal blooms

Numerous stagnant waters in Flanders are characterized by high nutrient concentrations, leading to severe algal blooms and under critical conditions to fish mortality. In this context, a eutrophicated pond was analysed hydrobiologically during one month in order to develop a management plan for the coming years to restore its ecological stability. Bergelenput (Wevelgem), a former sand pit, is now a nature reserve, currently also used for recreational fishing. During the last decade, incidental fish kills have occurred. The main cause is thought to be nutrient enrichment, enhancing algal blooms. The most probable source of these nutrients is fertiliser runoff from the surrounding fields characterised by intensive agricultural activities. Two possible causes of these fish kills, both associated with algal blooms, were considered during this preliminary study. The first was oxygen depletion of the water caused by algal respiration during the night. The second was related to the presence of Microcystis aeruginosa, a cyanobacterium known to be toxic sometimes and hence responsible for fish kills. Short-term and long-term management options are being developed within the context of this research to rehabilitate the ecosystem.