Study for water quality improvement in Kitakata Lake

This is a preliminary study for the water quality improvement in Kitakata Lake, Fukui, Japan, after the bilateral agreement made between Awara City and Fukui University of Technology in 2005. The water quality of Kitakata Lake has been chronically eutrophic. Over the last 20 years, Chemical Oxygen Demand (COD), Total Nitrogen (T-N) and Total Phosphorus (T-P) concentrations have remained on the same level, which violate the water quality standard imposed to the lake (classified as the type B and IV). The seasonal variation has shown that, in summer, pH, COD and T-P increase whereas Dissolved Oxygen (DO) and T-N decrease, which may be typical for eutrophic lakes. The analysis of incoming loads to the lake revealed that approximately 60% of COD, T-N and T-P originates from non-point sources like rice field, farm and forest, indicating the importance of measures against those sources