Long-term Changes in the Concentrations of Total Phosphorus and Nitrate in Some Quality Parameters of Water in Lake Biwa Using Integrated Analysis from Several Monitoring Data

Abstract

Some early monitoring data of the quality of water in Lake Biwa from 1962 to 2008 were collected and changes in the concentrations of nitrogen and phosphorus in water from the lake were analyzed to obtain an overview of eutrophication. Mean concentrations of phosphorus and nitrate-N in the past were assumed according to characterization of the horizontal distribution and seasonality of monthly monitoring data in the present, because the number of data in past total phosphorus and nitrate-N were small densities. The result shows that the peak concentrations of total phosphorus in the lake water occurred in the 1970s. The changes in the total phosphorus concentrations in the lake water harmonized with the phytoplankton biomass indicating the progress of eutrophication. A careful comparison of two or more sets of survey data with the characterization of water quality in the lake was effective to obtain an overview of time series data from the past.