Calculation of runoff pollution load from the upland field

Abstract

 The nutrient salt concentrations of inner bays or lakes are still not decreasing. The nutrient loads from non-point sources are large, however, the actual contribution of the loads to inner bays and lakes is not clarified. In this study the nutrients loads from the upland fields were evaluated by conducting river investigations and a specific load dose was calculated using the obtained data. 70% of annual precipitation has recorded between May and September and red tides were occurred in the Mikawa Bay in this term. Since the primitive unit of pollution load of upland fields established by the Ministry of Environment are based on the investigations in case of fine weather condition, TN and TP load ratios are 6.58kg/km²/day and 0.09kg/km²/day, respectively. The TN and TP load rations obtained using the data collected during rain events in this study were 2.94 and 1.0 in which the ratio of P was quite high.