Surface Water Chemistry, Particularly Concentrations of NO sub(3) super(-) and DO and delta super(15)N Values, Near a Tea Plantation in Kyushu, Japan

Most spring waters near tea plantations in southern Japan cannot be used for drinking water because they have nitrate levels above the recommended maximum concentration limit. The influence of fertilizers used at tea plantations on surface water, especially downstream from plantation catchments, was studied by analyzing time series of chemical concentrations and nitrogen isotopic ratios in local ponds. The major dissolved components of spring and river water originating from a plantation catchment were calcium, magnesium, nitrate, and sulfate ions. Soil enrichment with fertilizers and calcium and magnesium carbonates also lowered pH values in plantation soil. Despite acidic spring water flows into ponds, pond water pH usually was above 7. Variations in pH over a 3-4 month period ranged over four orders of magnitude. Pond pH increases were associated with a rise in DO and nitrogen isotope values, and a decline in nitrates, probably due to assimilation and production of oxygen by algal photosynthesis.