Chemical and Isotopic Compositions of Groundwater and Stream Water in a Heavy Agricultural Basin of Korea

Abstract

The chemical and isotopic compositions of groundwater and stream water in the Haean basin, Korea, which have been intensively used for agricultural irrigation, were examined. The field parameters and chemical compositions were typical of relatively uncontaminated waters, except for the agricultural impact. The low EC levels indicated that the waters had not experienced any significant geochemical processes such as water-rock interaction and evaporation. The very similar chemical compositions and ionic ratios were also indicative of fast circulation and good hydraulic connection. The oxygen and hydrogen isotopic compositions of most of the samples in wet and dry seasons showed very similar range which indicated a single source for both waters without any significant geochemical alteration. However, in the wet season, evaporation trends were observed in some groundwaters because of inflow of irrigation return flow from a rice paddy field. The isotopes of both waters were affected by the altitude and amount of precipitation.

Stream Water and Groundwater Interaction Revealed by Temperature Monitoring in Agricultural Areas

“…It is bordered by high elevation mountains with altitudes of 1147-1242 m. The lowermost area of the basin has an elevation of about 400 m. Forests cover the uppermost areas, while the lower areas are mostly used for agriculture. This unusually deep depression was formed by differential weathering between meta-sedimentary rocks at the outer rim and granites in the interior [29]. Alluvial deposits are found close to streams in the flat areas.…”

“…Most groundwater recharged by rainfall quickly reaches the stream. Therefore, the chemical compositions and isotopic compositions of groundwater are not significantly distinguished from those of stream water [29]. Geological investigations revealed that there are typically six hydrogeological layers in the lowlands: surface reclamation soil, sand and gravel, scree, weathered rock, soft rock with fractures, and fresh hard rock [28].…”

“…Geological investigations revealed that there are typically six hydrogeological layers in the lowlands: surface reclamation soil, sand and gravel, scree, weathered rock, soft rock with fractures, and fresh hard rock [28]. Groundwater levels measured during April-October 2008 in the lowlands were between 0.92 and 8.83 m (mean = 3.21 m) below the ground surface [29]. The annual mean air temperature measured at the center of the basin (at an automatic weather station; AWS) was 8.4 °C , but with a wide seasonal variation from a maximum of 26.0 °C in summer (July) to a minimum of −15.5 °C in winter (January).…”

“…The annual mean air temperature measured at the center of the basin (at an automatic weather station; AWS) was 8.4 °C , but with a wide seasonal variation from a maximum of 26.0 °C in summer (July) to a minimum of −15.5 °C in winter (January). The annual mean precipitation is approximately 1800 mm, with over 60% of precipitation in the summer season (June to August) [29]. The basin has experienced heavy agricultural use and much of the water supply depends on groundwater pumping (approximately 10 wells/km 2 in the agricultural area) [30].…”