沖縄県宮古島の水道水源窒素の由来と森林による窒素除去能の推定

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The amount and origins of nitrogen supplied in environment and groundwater were calculated for Shirakawata, Higashi-soedo and Hukusato groundwater basins from where drinking water is taken on Miyako Isl., Okinawa, Japan. The concentrations of inorganic nitrogen were surveyed monthly in 1995-1999 for groundwater in the basins. Also, nitrogen removal by forest was estimated by analyzing the correlation of surveyed/estimated ratio of groundwater nitrogen concentration with the forest area ratio. The amount of nitrogen supplied in the environment in the basins was calculated as 109.9-130.8 kg N ha^<-1> y^<-1>, of which 57.5-6l.6% was derived from fertilizers and 22.0-30.2% from livestock wastes. The surveyed concentrations of nitrogen in groundwater in the respective basins were 5.32,5.58 and 7.01 mg L^<-1>. The estimated concentrations of nitrogen were 7.89,6.77 and 7.65 mg L^<-1>, respectively, of which 48-50% was derived from fertilizers and 20-28% from livestock wastes. The forest area ratios in the basins were 24.2,19.8 and 14.2%, respectively. The correlation mentioned above was negative (y=- 4O.23x+51.77,R=0.980) and the capacity of nitrogen removal by forest was estimated at 36-84 kg N ha^<-1> y^<-1>.
2001-06-05