Approaches to enhance biodiversity in a eutrophic inner bay of Lake Biwa

Author(s): Yoshiaki Kohno
Email (s):
Institution or organization of origin: NPO Biwako Houjyounosato
Country: Japan


Despite improvement in lake water eutrophication, fish stock recovery in many lakes is limited. Thus, the importance of near-shore biodiversity, damaged by shoreline restructuring and escalated eutrophication by flow-in sludge and secondary photosynthetic production, has been widely recognized. To find feasible and sustainable ways enhancing biodiversity, feasibility of the following approaches has been tested at an inner bay connected to Akanoi bay of Lake Biwa with careful observation of the ecosystem. Firstly, to enable environmentally stable habitats, 3 connected rafts with different surface depths have been prepared, as annual change in water level usually exceeds 50cm. On the rafts, various kinds of irises, waterlilies and wild aquatic plants grew fast with nutrients in water and soil containing sludge from the bay bottom. Especially, connected ecosystems giving variety in living conditions showed wider biodiversity.Secondly, to minimize adverse effects from disturbed sludge in a shallow water zone, improved rearing methods were introduced, such as keeping bivalves in a mesh bag above the bay bottom and serving a sludge shelter zone to zooplanktons and other aquatic animals depending on filtration diet.Thirdly, crayfish dominance found to be the major reason of scarcity of algae and submerged plants which give hiding place for aquatic animals including juvenile fish, needed control and introduction of protection system against them. Despite the study being limited in space and duration, the integrated trials to make an attractive zone for fish revealed feasibility and expandability.

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