Abstract
Constructed lakeshores occupy 73％ of the shoreline in the southern basin of Lake Biwa and 38％ in the northern basin. To elucidate the effect of lakeshore construction on the sediment of coastal zone, sediments were sampled from coastal zones near constructed shorelines and near natural shorelines, and were characterized by their particle size distribution, chemical components, and depth distributions of dissolved oxygen （DO） and microalgae cells. A micro profiling system with a micro DO sensor was used for determining DO concentration in the sediment every 0.5－1.0-mm layer. The microalgae cells were counted under an epifluorescence microscope every 1-mm sediment layer. As a result, the sediments near constructed lakeshores were anaerobic with a thin aerobic layer at the sediment surface and contained fine clay silt more than 50％ in volume, whereas the percentages of fine clay silt in the sediments near natural lakeshores were not more than 1.3％. Furthermore, much higher cyanobacteria was detected in the sediments near constructed lakeshores than near natural lakeshores. Thus, it was suggested that the lakeshore construction made the sediments in the coastal zone more anaerobic and contributed to the predomination of cyanobacteria. However, further researches will be required for the better understanding of the effect of lakeshore construction in detail.
