Abstract
The aim of this study was to estimate the removal effects of runoff loads in an irrigation reservoir. The watershed of the irrigation reservoir is a tea field zone in Shizuoka prefecture. The annual average T-N concentration of the Tanno reservoir was particularly high, being 24.5 mg·l-1. On the other hand, the T-P and COD concentrations were very low, being 0.02 mg·l-1 and i.e, 1.8mg·l-1, respectively, and living things such as aquatic plants were not observed, which is very rare in such an irrigation reservoir. Compared to the inflow water of the irrigation reservoir, the effluent water had wide ranges of changes in the concentrations of NO2-N, T-P. However, the changes in other water quality parameters were in contrast to these three parameters. The NH4-N, NO3-N, T-N, K+,Na+,Mg2+,Al3+, Cl- and SO42- effluent loads were smaller than the influent loads, and there were reductions in the loads in the irrigation reservoir. The Ca2+ and T-P effluent loads increased due to production load from the sediment, and this effluent load was larger than the influent load. The total T-N influent load was 73848kg·y-1, the annual reduction load was 6516kg·y-1, and the removal rate was 337mg·m-2 per day.
