2011 年 67 巻 4 号 p. I_583-I_588
Groundwater pollution by nitrate due to agricultural activities has become serious environmental issues in the two shirasu plateaus of Kasanohara and Kanoyabaru of Osumi peninsula, Kagoshima prefecture. We developed a groundwater recharge model and examined the water budget characteristics. Furthermore, two-dimensional numerical simulations were carried out to evaluate the effects of countermeasures for the contaminated source. The results of water balance analysis showed that runoff is 10-15%, groundwater recharge is 65%, and evapotranspiration is 20-25% of precipitation in the catchment area. The numerical results indicate that it takes 50 years for Kasanohara and 80 years for Kanoyabaru to display the effects of countermeasure of 80% reduction in concentration of the source zone. The long-term numerical simulation suggested that detailed recharge rate fluctuation rather than constant recharge rate should be applied.