Groundwater Quality in Collective Tea Fields and Estimation of Nitrogen and Phosphorus Outflow

Abstract

The study area was located in the Makinohara collective tea fields in Shizuoka, Japan. There are flourishing tea industries in this area. The quality and level of the groundwater were observed from Jun. 2002 to Sept. 2003 and examined on the basis of hydrogeology. The Makinohara plateau comprises of clay layers between gravel beds. It yielded discontinuous water qualities caused by perched water in a geological structure. The average concentrations of T-N and NO₃-N in the surface water were 26.4 mg·l^-1, 23.8mg·l^-1, respectively. In contrast, for the groundwater, these concentrations were 17.2 mg·l^-1 and 12.6 mg·l^-1, respectively. The average concentrations of T-P were 0.012 mg·l^-1 in the surface water and 0.022 mg·l^-1 in the groundwater. This difference is caused by the dilution effect and release of phosphorus from on aquifer. The annual groundwater effluent loads of nitrogen and phosphorus from the catchments of the Makinohara plateau were 406 t·y^-1 and 0.7 t·y^-1, respectively.