Source and distribution of nitrate contamination in alluvial groundwater in a riverside agricultural field, Buyeo area
Jang-Soon Kwon
1,*
․Gi-Tak Chae
2
․Seong-Taek Yun
1
․Byoung-Young Choi
3
1
Department of Earth & Environmental Sciences, Korea University, [email protected]
2
Korea Institute of Geoscience and Mineral resources
3
Korea Atomic Energy Research Institute
Major ions and stable isotopic (Dw
ater,
18
Ow
a
ter,
15N
ni
t
rate, 1
8On
it
r
ate) me
asurements in concert with hydrochemical modeling were used in order to elucidate the sources and geochemical processes controlling nitrate contamination of shallow alluvial groundwater underneath a riv- erside agricultural field in the Buyeo area, Korea. Beneath vegetable fields in the sandy soil the mean nitrate concentration of groundwater was 148.6 mg/L, which is significantly higher than in groundwater (mean 28.8 mg/L) beneath silty soils underneath rice paddy fields.
Nitrogen isotope data indicate that synthetic fertilizers are the predominant source of ground- water nitrate in the study area. Denitrification during recharge through rice paddy soils appears to be responsible for the lower nitrate concentrations in groundwater beneath the silty soil zone. The relationship between nitrogen and oxygen isotope data of nitrate suggests also the mixing of two different groundwater bodies with nitrates from the silt zone and the sand zone.
Geochemical mass balance modeling on hydrochemical data indicate that various agricul- tural chemicals such as urea, lime, magnesium sulfate and potassium chloride dissolve in vegetable fields of the sand zone, resulting in significant enrichments of various solutes such as K
+
, Ca
2+
, Mg
2+
, NO
3,
SO4
2 a
nd Cl.
I
n addition to the over-used synthetic nitrogen fertilizers, the aerobic condition of the sand zone results in a high nitrate vulnerability of groundwater.
Nitrate contamination of the Buyeo area is caused by overuse of nitrogen fertilizers and is enhanced by the geologic characteristics of the soils. This study suggests that a reduction of over-fertilization especially on vegetable fields in the riverside sand zone is required to minimize the nitrate contamination of groundwater. The integrated use of hydrochemical and isotopic data will be useful for managing the groundwater quality in riverside alluvial sand aquifers where intensive agricultural activity occurs.
