論文
湖沼・内湖の物質循環 - 生態系モデルによる生物学的水質浄化機能の評価 -
2001 年 7 巻 1+2 号 p. 31-52
詳細
2001 年 7 巻 1+2 号 p. 31-52
One of the effective measures to cope with eutrophication of lake waters is to remove nutrient substances that can cause to algal blooming, by taking advantage of the natural capability of water purification. Here the term 'purification' is defined, in a wide sense, as a potential role of the lake contributing to reduction of pollutants and thus restraint to eutrophication; in which various pro cesses concerning seasonal nutrient fixation such as uptake by aquatic plants, attachment to foli age substrates and feeding by organisms of higher-trophic level are regarded as biological purifi cation processes together with eternal losses or removals from waters. In order to evaluate the purification capacity, a numerical lake ecosystem model was developed highlighting on the role of macrophyte colonies that inhabit alongshore, and applied to Lakes Suwa, Kasumi, Biwa and five attached sublakes of Lake Biwa. The model takes account of the biological interactions between pelagic compartments (phytoand zooplankton, detritus, dissolved organic matter, pelagic fish and nutrients) and benthic com partments (macrophytes, attached algae, attached small animals, macro- and megalobenthos and demersal fish). Under the time-dependent conditions of meteorological and hydraulic factors, the model was run over a year to evaluate annual nutrient budget and purification capacity of each lake. The results revealed that the purification capacity is generally estimated, from the stand points of both stock and flux, higherin the shoreregion than in the offshoreregion becauseof a wide variety of organisms including aquatic plants. Moreover,it almost increases in proportion to vegetation densityof the shoreregion.Nutrientfluxes associatedwith purificationprocessesturned out closely related to surfacearea or equivalently to retentiontime of lake waters,suggestingthat the biological purificationdoes not becomedominantagainst physical turnoveruntil the surface area reaches around 103 ha or the retention time exceeds around 10^2 days.
