25 巻 (2002) 11 号 p. 635-640
Various countermeasures have been taken against eutrophication in lake. However, such countermeasure may increase CO2 emission even if lake water quality is improved. An integrated evaluation of such trade-off is necessary in terms of comprehensive environmental improvement. The objectives of this study are to develop and apply an integrated assessment method of the improvement of water environment by multiple countermeasures and the impact of global warming by additional CO2 emission. The method comprised the quantification of reduced water pollutants and additional CO2, estimation of environmental improvement and impact, economic evaluation and the comparison of them. Along with the method, multiple countermeasures against point source and non-point source for environmental improvement of Lake Suwa in Nagano Prefecture were evaluated. Environmental improvement in Lake Suwa was simulated by applying an ecosystem model and its economic value was estimated by applying the Contingent Valuation Method. On the other hand, CO2 emission was calculated by applying an inventory analysis of Life Cycle Assessment, and the economic value of global warming was estimated by using marginal social costs. It is inferred that the completion of sewerage systems and the change of fertilization practices are effective within environmental aspects of eutrophication and global warming.