Surface water chemistry, particularly concentrations of NO3- and DO and delta15 N values, near a tea plantation in Kyushu, Japan
1997
Ii, H. | Hirata, Toshimi | Matsuo, H. | Nishikawa, M. | Tase, N.
To investigate the influence of chemical fertilizers on drinking water neighboring tea plantations in Kyushu, Japan, time series of chemical concentrations and nitrogen isotopic ratios within local ponds were studied. Results indicated that the main dissolved components of spring and river water originating from a tea plantation catchment were Ca(2+), Mg(2+), NO3(-), and SO4(-2). Furthermore, pH values were below 7 due to plantation soil enrichment using nitrogen fertilizers and calcium and magnesium carbonates. Although acidic spring water flowed into a local pond, the pH value of the pond water remained mostly above 7. Occasionally, excessive spring water influx after heavy rains caused the pond water pH to dip below 7. The pond water showed temporal variations of pH ranging over 4 orders of magnitude within a 3-4 month period. The increase in pH values within the pond was associated with an increase in dissolved, oxygen (DO) and delta 15N values and the partial disappearance of NO3(-). This is explained by nitrogen assimilation and production of oxygen during photosynthesis by algae.
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