HR: 1340h
AN: H43C-1510    [Abstracts]
TI: Seasonal Variations of Biogeochemical Characteristics in Predominantly Anaerobic Groundwater From a Riverine Alluvial Aquifer
AU: * Koh, D
EM: chankoh@kigam.re.kr
AF: Korea Institute of Geoscience & Mineral Resources, 92 Gwahang-no, Yuseong-gu, Daejeon, 305-350, Korea, Republic of
AU: Ha, K
EM: hasife@kigam.re.kr
AF: Korea Institute of Geoscience & Mineral Resources, 92 Gwahang-no, Yuseong-gu, Daejeon, 305-350, Korea, Republic of
AU: Kim, K
EM: kangjoo@kunsan.ac.kr
AF: Kunsan National University, san 68, Miryong-dong, Kunsan, 573-701,
AU: Ko, K
EM: kyungsok@kigam.re.kr
AF: Korea Institute of Geoscience & Mineral Resources, 92 Gwahang-no, Yuseong-gu, Daejeon, 305-350, Korea, Republic of
AB: Hydrogeochemical parameters were investigated for groundwater from six multi-level wells (up to 30 m deep) in a riverine alluvial aquifer with intense agricultural activities of rice, barley and vegetable cultivation during two sampling campaigns in rainy summer (July) and dry spring (March) season to identify seasonal variation in biogeochemical processes in the aquifer. The alluvial aquifer is located in flooldplains of Mangyeong River, western part of South Korea near the city of Jeonju. pH, concentrations of Na, Cl, Ca, F have little difference between the two sampling periods. Electrical conductivity (EC) and concentrations of HCO₃, Mg, SO₄ slightly increased as a whole from rainy season to dry season. Dissolved concentrations of major ions in river water increased by more than three fold during the seasons. These feature indicates that the groundwater system is relatively stable and less affected by the river in hydrogeochemical aspects. Dissolve oxygen (DO) concentrations were less than 1 mg/L for most of the wells whereas two wells turned to aerobic conditions in dry season which can be attributed to removal of stagnant water in the paddy fields. NO₃ concentrations decreased significantly in dry season at most well points near the paddy fields. This indicates that denitrification is dominant over nitrate supply by infiltrating water from the land surface which is likely to be significantly decreased after harvesting of rice during the dry season. However, NO₃ increased in upper zones (<10 m) in two wells near the barley and vegetable fields, which suggest continued nitrate supply from the crop fields to the upper part of the aquifer during the season. Fe concentrations have relatively small variations in most of wells for two sampling periods. However, from rainy season to dry season, Fe concentrations significantly increased more than two fold in two wells whereas NO₃ concentration decreased below detection limit from 2 to 8 mg/L. The increase of Fe resulted in the increase of HCO₃ concentrations by two fold and significant increase of EC, which even transformed hydrogeochemical pattern of major ions in those intervals, which can be attributed to the much higher proton consumption in iron reduction than in denitrification. This is indicative of the seasonal change in electron-accepting processes from nitrate reduction to iron reduction along with decrease in nitrate supply from the land surface. Seasonal variations in concentrations of DO, NO₃, and Fe show that the temporal change in agricultural activities on land surface significantly affects biogeochemical processes in an alluvial aquifer. Denitrification of agriculturally derived NO3 and iron reduction in the alluvial aquifer can significanlty affect water chemistry of the river.
DE: 0402 Agricultural systems
DE: 0469 Nitrogen cycling
DE: 0471 Oxidation/reduction reactions (4851)
DE: 0483 Riparian systems (0744, 1856)
SC: Hydrology [H]
MN: 2007 Fall Meeting