Nitrate contamination and subsequent hydrogeochemical processes of shallow groundwater in agro-livestock farming districts in South Korea

Ho Rim Kim, Soonyoung Yu, Junseop Oh, Kyoung Ho Kim, Jeong Ho Lee, Md Moniruzzaman, Hyun Koo Kim, Seong Taek Yun

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Abstract

In last several decades, the nitrogen cycle has been significantly perturbed, largely due to intensification of agricultural activities throughout the world. In this study, we examined the impact of agricultural N inputs on the quality and chemistry of shallow groundwater, based on a large hydrochemical dataset (n ≈ 4000) collected from 100 agro-livestock farming districts in South Korea. The South Korean groundwater, studied mostly in silicate aquifers, shows very high nitrate concentrations (median NO3 = 22.2 mg/L) and acidification (median pH = 5.6). The groundwater nitrate levels tend to increase with the estimated N loadings, and the groundwater pH generally decreases with increasing nitrate levels. The relationship between the concentrations of Ca2+ + Mg2+ and HCO3- has a moderate adjusted R2 value (0.4), and the molar (Ca2+ + Mg2+) / HCO3- ratios (r) tend to increase with nitrate concentrations. This implies that the chemical composition of the groundwater is controlled by multiple hydrogeochemical processes, which include weathering of silicates and carbonates induced by carbonic acid (r = 0.5), nitrification (r ≥ 1) and denitrification (mostly, r < 0.5 in this study). In particular, undrinkable (NO3 > 44.3 mg/L) groundwater (n = 988) shows an average molar ratio of 1.04, indicating that such highly contaminated groundwater experiences the enhanced geochemical weathering of aquifer materials by an anthropogenic process (e.g., addition of N fertilizers). The results of principal component (PC) analysis also support our explanation: the first PC shows significant negative correlations with major components including NO3 while there is a weak positive correlation with pH, indicating anthropogenically enhanced weathering that includes the buffering process by agricultural liming materials, while the second PC shows negative correlations with Eh, DO and NO3 but positive correlations with pH and HCO3 , suggesting the denitrification process. A few groundwater samples (about 4%) experienced heterotrophic denitrification, and they have molar ratios (r) of less than 0.5. The results of this study indicate that 1) geochemical weathering of aquifer materials in shallow groundwater systems is enhanced by nitrate contamination caused by high N loadings in agro-livestock farming districts, causing increased salinity, and 2) in silicate aquifers, the prevailing hydrochemical process can be interpreted by the molar (Ca2+ + Mg2+) / HCO3- ratios of groundwater.

Original languageEnglish
Pages (from-to)50-61
Number of pages12
JournalAgriculture, Ecosystems and Environment
Volume273
DOIs
Publication statusPublished - 2019 Mar 1

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livestock farming
South Korea
groundwater
livestock
farming systems
nitrates
nitrate
weathering
aquifers
silicates
denitrification
aquifer
silicate
calcium
contamination
carbonic acid
liming materials
nitrogen cycle
liming
buffering

Keywords

  • Agro-livestock farming
  • Enhanced weathering
  • Nitrate contamination
  • Nitrification and denitrification
  • Shallow groundwater
  • South Korea

ASJC Scopus subject areas

  • Ecology
  • Animal Science and Zoology
  • Agronomy and Crop Science

Cite this

Nitrate contamination and subsequent hydrogeochemical processes of shallow groundwater in agro-livestock farming districts in South Korea. / Kim, Ho Rim; Yu, Soonyoung; Oh, Junseop; Kim, Kyoung Ho; Lee, Jeong Ho; Moniruzzaman, Md; Kim, Hyun Koo; Yun, Seong Taek.

In: Agriculture, Ecosystems and Environment, Vol. 273, 01.03.2019, p. 50-61.

Research output: Contribution to journalArticle

Kim, Ho Rim ; Yu, Soonyoung ; Oh, Junseop ; Kim, Kyoung Ho ; Lee, Jeong Ho ; Moniruzzaman, Md ; Kim, Hyun Koo ; Yun, Seong Taek. / Nitrate contamination and subsequent hydrogeochemical processes of shallow groundwater in agro-livestock farming districts in South Korea. In: Agriculture, Ecosystems and Environment. 2019 ; Vol. 273. pp. 50-61.
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AU - Lee, Jeong Ho

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AU - Kim, Hyun Koo

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N2 - In last several decades, the nitrogen cycle has been significantly perturbed, largely due to intensification of agricultural activities throughout the world. In this study, we examined the impact of agricultural N inputs on the quality and chemistry of shallow groundwater, based on a large hydrochemical dataset (n ≈ 4000) collected from 100 agro-livestock farming districts in South Korea. The South Korean groundwater, studied mostly in silicate aquifers, shows very high nitrate concentrations (median NO3 − = 22.2 mg/L) and acidification (median pH = 5.6). The groundwater nitrate levels tend to increase with the estimated N loadings, and the groundwater pH generally decreases with increasing nitrate levels. The relationship between the concentrations of Ca2+ + Mg2+ and HCO3- has a moderate adjusted R2 value (0.4), and the molar (Ca2+ + Mg2+) / HCO3- ratios (r) tend to increase with nitrate concentrations. This implies that the chemical composition of the groundwater is controlled by multiple hydrogeochemical processes, which include weathering of silicates and carbonates induced by carbonic acid (r = 0.5), nitrification (r ≥ 1) and denitrification (mostly, r < 0.5 in this study). In particular, undrinkable (NO3 − > 44.3 mg/L) groundwater (n = 988) shows an average molar ratio of 1.04, indicating that such highly contaminated groundwater experiences the enhanced geochemical weathering of aquifer materials by an anthropogenic process (e.g., addition of N fertilizers). The results of principal component (PC) analysis also support our explanation: the first PC shows significant negative correlations with major components including NO3 − while there is a weak positive correlation with pH, indicating anthropogenically enhanced weathering that includes the buffering process by agricultural liming materials, while the second PC shows negative correlations with Eh, DO and NO3 − but positive correlations with pH and HCO3 −, suggesting the denitrification process. A few groundwater samples (about 4%) experienced heterotrophic denitrification, and they have molar ratios (r) of less than 0.5. The results of this study indicate that 1) geochemical weathering of aquifer materials in shallow groundwater systems is enhanced by nitrate contamination caused by high N loadings in agro-livestock farming districts, causing increased salinity, and 2) in silicate aquifers, the prevailing hydrochemical process can be interpreted by the molar (Ca2+ + Mg2+) / HCO3- ratios of groundwater.

AB - In last several decades, the nitrogen cycle has been significantly perturbed, largely due to intensification of agricultural activities throughout the world. In this study, we examined the impact of agricultural N inputs on the quality and chemistry of shallow groundwater, based on a large hydrochemical dataset (n ≈ 4000) collected from 100 agro-livestock farming districts in South Korea. The South Korean groundwater, studied mostly in silicate aquifers, shows very high nitrate concentrations (median NO3 − = 22.2 mg/L) and acidification (median pH = 5.6). The groundwater nitrate levels tend to increase with the estimated N loadings, and the groundwater pH generally decreases with increasing nitrate levels. The relationship between the concentrations of Ca2+ + Mg2+ and HCO3- has a moderate adjusted R2 value (0.4), and the molar (Ca2+ + Mg2+) / HCO3- ratios (r) tend to increase with nitrate concentrations. This implies that the chemical composition of the groundwater is controlled by multiple hydrogeochemical processes, which include weathering of silicates and carbonates induced by carbonic acid (r = 0.5), nitrification (r ≥ 1) and denitrification (mostly, r < 0.5 in this study). In particular, undrinkable (NO3 − > 44.3 mg/L) groundwater (n = 988) shows an average molar ratio of 1.04, indicating that such highly contaminated groundwater experiences the enhanced geochemical weathering of aquifer materials by an anthropogenic process (e.g., addition of N fertilizers). The results of principal component (PC) analysis also support our explanation: the first PC shows significant negative correlations with major components including NO3 − while there is a weak positive correlation with pH, indicating anthropogenically enhanced weathering that includes the buffering process by agricultural liming materials, while the second PC shows negative correlations with Eh, DO and NO3 − but positive correlations with pH and HCO3 −, suggesting the denitrification process. A few groundwater samples (about 4%) experienced heterotrophic denitrification, and they have molar ratios (r) of less than 0.5. The results of this study indicate that 1) geochemical weathering of aquifer materials in shallow groundwater systems is enhanced by nitrate contamination caused by high N loadings in agro-livestock farming districts, causing increased salinity, and 2) in silicate aquifers, the prevailing hydrochemical process can be interpreted by the molar (Ca2+ + Mg2+) / HCO3- ratios of groundwater.

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KW - Enhanced weathering

KW - Nitrate contamination

KW - Nitrification and denitrification

KW - Shallow groundwater

KW - South Korea

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