都市域の地下水における無機態窒素の組成と分布

Abstract

Distribution, composition and possible sources of nitrate and ammonia nitrogen (N03-N, NH4-N) in ground water in Osaka City area were studied. Osaka City has area been developed on the alluvial lowland, where the diluvial terrace extends nearly from north to south within the center of area. Ground water collected from the terrace showed the tendency : NO3-N >> NH4-N and vice versa in these from its surrounding plain.The land-use distribution in city area is 1.1% for agricultural field, and 99% of city area was serviced by municipal sewerage. Therefore, the load of nitrogen from the use of chemical fertilizers, the inadequate disposal of human excreta and domestic sewage are small.The main source of inorganic nitrogen may be the pore water involving NH4-N squeezed out with self-compaction of holocence clay bed lying on the aquifer. Such could be seen in the land subsidence of coastal area due to vigorous pumping of ground water in the past. The terrace play a role of the recharge area for the related aquifers in the pain, and so infiltrated surface water has considerable amount of oxygen. NO3-N was considered to result from the nitrification of NH4-N from the clay bed or only maintained in water dissolving oxygen.