| Abstract: | Ground water from springs and public supply wells was investigated for hydrochemistry and environmental isotopes of 3H, 18O and D in Jeju volcanic island, Korea. The wells are completed in a basaltic aquifer and the upper part of hydrovolcanic sedimentary formation. Nitrate contamination is conspicuous in the coastal area where most of the samples have nitrate concentrations well above 1 mg NO3? N/l. Agricultural land use seems to have a strong influence on the distribution of nitrate in ground water. Comparison of stable isotopic compositions of precipitation and ground water show that ground water mostly originates from rainy season precipitation without significant secondary modification and that local recharge is dominant. 3H concentration of ground water ranged from nearly zero to 5 TU and is poorly correlated with vertical location of well screens. The occurrence of the 3H‐free, old ground water is due to the presence of low permeability layers near the boundary of the basaltic aquifer and the hydrovolcanic sedimentary formation, which significantly limits ground water flow from the upper basaltic aquifer. The old ground water exhibited background‐level nitrate concentrations despite high nitrate loadings, whereas young ground water had considerably higher nitrate concentrations. This correlation of 3H and nitrate concentration may be ascribed to the history of fertilizer use that has increased dramatically since the early 1960s in the island. This suggests that 3H can be used as a qualitative indicator for aquifer vulnerability to nitrate contamination. Copyright © 2005 John Wiley & Sons, Ltd. |
