Author(s): Fatos Kerciku; Yoshiyuki Nakamura; Inoue Tetsunori
Linked Author(s):
Keywords: Nutrient recycling; Continuous flow system; Batch system; Eutrophication; Bivalve
Abstract: Various research works have been conducted during the last decade emphasizing the role of metabolic processes of different suspension feeding bivalves in lakes. However, only a few such studies have been concerned with Corbicula japonica, which is the most popular brackish-water species in Japan. C. japonica is a tiny suspension-feeding bivalve very abundant in the littoral region of Lake Shinji, Japan. Although the lake is well fed with nutrients, it still remains less eutrophied than other lakes with comparable external nitrogen and phosphorus loadings. Also, less turbid water often develops in littoral regions of the lake where bivalves dominate. Attributing these facts to the functional role of C. japonica, we have adapted a microcosm approach utilizing a continuous-flow microcosm and a batch system technique subjected to several selected temperature conditions to assess the bivalve's role in lake ecosystem.?? Results show that filtration, excretion and respiration rates of C. japonica significantly depend on temperature having a maximum value for temperatures close to 25 ° C. Also C. japonica selectively grazes phytoplankton with high content of Chl. a, creating a possibility for the change of the phytoplankton composition in the lake. C. japonica shortcuts the internal nutrient circulation, excreting ca. 87 % of the nitrogen uptake and ca. 60 % of the phosphorus uptake. At the end, the laboratory results were extrapolated to the scale of the whole lake and the mass balance of nitrogen and phosphorus for summer and wintertime was evaluated. The fisheries output consisted 15 % of external loading of River Hii, it is suggested that C. japonica is very efficient tool for natural eutrophication control during summertime. Also, it results that abatement of pollutant loading is a necessary but insufficient step toward improving and restoring water quality and quantity, and ecosystem function.
Year: 2001