Dissolved nitrogen concentration in river water and its impacts on downstream brackish-estuary lakes in the Bekanbeushi River and Lake Akkeshi catchment, northern Japan

Abstract To clarify the effects of land use in a catchment on river water quality, its nutrient environment and primary production in downstream brackish-estuary lakes, we observed nutrient concentrations (nitrogen and phosphorus) in river and lake water and analyzed land use in the catchment. The concentration of nitrate-nitrogen tended to increase in river water associated with a high percentage of agricultural land (pastureland) in its catchment. It is suggested that nitrogen management in agricultural lands in the catchment area and the arrangement of forests and riparian wetlands and their nitrogen removal functions may have an important effect on the productivity of aquatic organisms and food webs in downstream lakes, especially near river estuaries.