The effects of cattle farming and snowfall to the eutrophication of Oshima-Ohnuma in Hokkaido

Abstract

A comparative study of the interannual change of water quality in a eutrophic lake, Oshima Ohnuma in Hokkaido, between 1984-2005 and 2009-2021 showed that the main factor of the change in COD 75％ value was the number of beef cattle in the basin before 2005, but it was the maximum snow depth (MSD) in the previous winter since 2009. This change since 2009 may be due to the recent reduction of livestock load, and the climate change to amplify the interannual change in MSD. The dilution effect by snowmelt water on the lake water seemed to change the interannual change in COD value. As a future measure to suppress the eutrophication of the lake, it was proposed to introduce a livestock load adjustment system that predicts the upper limit of compost use for each cattle farm in the basin according to MSD in the previous winter.