Proposed the Model for Estimation of Nitrogen Load in the Agro-Forestry Watershed

Abstract

Increasing nitrogen concentration in the river water caused by agricultural activities was reported in the Tokachi River basin, Hokkaido, Japan. The water quality conservation is required for the compatibility between the agricultural production and the environmental protection. It is important to analyze the nitrogen load in the watershed for water quality restoration. Nitrogen load is estimated by the nitrogen concentration in the river water and the water discharge. However, this model needs frequent samples of the nitrogen concentrations and water discharges. Also, many observations at multipoint have been required to figure out where and how much the nitrogen load occurs in the watershed. Here, we proposed a model to estimate the nitrogen load by land use in a watershed. The land use data such as watershed area and land use classification could be taken easily from a satellite image. Also, it can estimate the nitrogen load at any investigation point by using land use data for the estimation model. In the Tokachi River basin, the nitrate-nitrogen concentration in the river water had a positive correlation with the proportion of agricultural land in the watershed. Further, the water discharge was proportional to the watershed area. Thus, the estimation model of nitrogen load could be substituted the nitrogen concentration with the proportion of agricultural land, and the watershed discharge with the watershed area. From this, there is a high possibility to estimate the nitrogen load in the watershed by the agricultural land area in the Tokachi River basin. Future subject of this model is how to correct for the variations of nitrogen concentration and river water discharge at different investigation periods.