2013 Volume 4 Issue 2 Pages 56-61
In this study, the characteristics of nitrogen in river water at the normal water level were examined for a period after the enforcement of animal waste regulation. The differences in agricultural land use in the two study sites in Eastern Hokkaido were taken into consideration. In 35 watersheds in the two areas, the total nitrogen (T-N), nitrate nitrogen (NO3-N), nitrite nitrogen (NO2-N) and ammonium nitrogen (NH4-N) concentrations, and the river discharges were investigated. A total of 7 investigations were carried out during the period from late May to late November 2005. In the Tokachi area (24 watersheds), the main land uses are upland and dairy farming. In the Nemuro area (11 watersheds), the main land use is large-scale dairy farming. Irrespective of the land use in the watershed, when the proportion of the agricultural land was about 20% or lower, the value obtained by adding the standard deviation to the annual mean T-N concentration of river water in many investigated watersheds was 1.0 mg/L or lower. When watersheds whose proportion in the agricultural land was 65% or higher were examined, there were some whose values obtained by adding the standard deviation to the annual mean T-N concentration were close to 10 mg/L. Decreasing trends were not identified in the nitrogen concentration in river water investigated in the first year after enforcement of animal waste regulation. From the viewpoint of water quality conservation, it is effective to appropriately adjust the use of chemical fertilizers in the cropland in the watersheds and to encourage dairy farmers to practice appropriate management of livestock manure.
