The farming in that area is given public goods such as flood control, underground water cultivation and oxygen production to the residents in the lower area. These functions are very important for a human being, but have never been evaluated in terms of money.
Farmers recently use a larger amount of artificial fertilizers and agricultural chemicals.
As a result, there is concern that the water environment will be contaminated. The main aim of this paper is to clarify the present relationship between the above-mentioned two factors and water quality of rivers. The water samples were taken about once a week from May 12 at upper and lower ends of canals in two areas. Therefore, it is very important to carry out the low input agriculture also in Japan in order to prevent the water environment from getting worse.