Restoration and Conservation of Brackish Environments after the Termination of the Nakaumi Reclamation Project

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Working toward the restoration and sustainable utilization of the brackish environment of Lake Nakaumi, which has deteriorated significantly due to the reclamation project, the following studies were carried out ; (A)exploring and analyzing existing data, (B)accumulating new data mainly using a ecotechnological approach and running an environmental simulation based on these data, and (C)taking steps for conservation and management of a healthy environment in this brackish lagoon. The following areas were emphasized in research activities : coastal ecosystems, water quality, bottom environment and environmental remote sensing.Coastal ecosystem : The thanatobiologic condition of the bivalve Ruditapes philippinarum is controlled not only by water quality, but by lake basin shape, algal blooms, and the saprogenic effects of aquatic plants. This research provides important guidelines for the conservation of this filter-feeding bivalve, which will, in turn, promote bio-cleansing of the water … More column.Water quality : A maintenance-free observation unit and cost-effective data transmission system, necessary for long-term water quality monitoring in estuarine areas, was designed.Bottom environment : Based on sediment core analyses, an indicator of permanent sub-oxic to anoxic water is a sediment accumulation rate of less than 1kg/m2/yr and TOC greater than 3% when water depth is more than 15m in an enclosed coastal lagoon. In the sublittoral zone, the bottom topography was greatly modified by erosion and large masses of dead seaweed accumulated on the inner side of offshore breakwaters.Environmental remote sensing : The validity of wide-area environmental observation of the coastal lagoon environment was tested using satellite and airborne sensor data, Water-surface signatures interpreted from SAR data (JERS-1 and RADARSAT-1) showed a good correlation with wind direction and speed.These results were applied to computer simulation experiments investigating the alleviation of hypolimnetic anoxic conditions in Lake Nakaumi.In January of 2004 an international seminar was held to summarize and disseminate the results of this project. The following features were emphasized : (1)the importance of long-term monitoring, (2)the importance of citizen's consensus, (3)the need for any economic benefit analysis to include the concept of ecosystem goods and services, and (4)the need for the integration of research and education programs on this problem. Less