摘要：On the basis of the chemical components found in Lake Biwa, Japan from May 1963 to May 2008, the vertical variation (0~70 m depth) of total phosphorus (TP) and total nitrogen (TN) concentrations in the Northern Basin (Ie-1) were evaluated. Similarly, TP and TN concentrations were also discussed at the surface of the Southern basin (Nb-5). It was concluded that the second stage nutrient concentrations had decreased compared to Northern basin due to increased macrophyte growth, improvement in inflow river waters and implementation of laws. The long term variations in the TN/TP ratios were also discussed in relation to propagation of plankton. The lower TN/TP ratios observed in the Northern and Southern Basins waters were well coincident with the more frequent and denser propagation of N2-fixing cyanobacteria. Recently, the TN/TP ratios have shown a tendency of increase in Southern Basin suggesting a first sign for the restoration of water.
关键词：lake biwa; total phosphorus; total nitrogen; vertical distribution; long term trends
