ANALYSIS OF WATER QUALITY TRENDS IN OSAKA BAY WITH A WEIGHTED REGRESSION APPROACH

摘要

Understanding of physical, chemical and biological characteristics of the coastal areas is essential for the qualitative analysis of driving factors for the change in the ecosystem as a whole. Trends of historical water quality parameters and their relationship help in better understanding of how the parameters are changing with climate and terrestrial forcings. In this study, the trends of dissolved inorganic nitrogen (ammonium, nitrateitrite, sum of former two) in the Osaka bay is modelled with a weighted regression approach. The Weighted Regressions on Time, Discharge, and Season (WRTDS) is adapted for the bay area to improve the long term changes in dissolved inorganic nitrogen. Modelled trends showed that the nutrient concentration is declining except in the 90~(th) percentile. The predicted trends of the dissolved inorganic nitrogen is higher in the current years than the observed values. The trend of all forms of nitrogen in three groups of the Osaka bay, near to the coastline, in mid and the seaward side is analysed.