Nitrate Legacy in a Tropical and Complex Fractured Volcanic Aquifer System
Nitrate Legacy in a Tropical and Complex Fractured Volcanic Aquifer System
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DOI：
10.1029/2023jg007554
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发表时间：
2023-07
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影响因子：
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通讯作者：
R. Sánchez-Gutiérrez;R. Sánchez‐Murillo;G. Esquivel‐Hernández;C. Birkel;J. Boll;L. Rojas‐Jiménez;L. Castro-Chacón
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作者：
R. Sánchez-Gutiérrez;R. Sánchez‐Murillo;G. Esquivel‐Hernández;C. Birkel;J. Boll;L. Rojas‐Jiménez;L. Castro-Chacón
硝酸盐遗产正在影响整个热带地区的地下水资源。本研究描述了四十年来哥斯达黎加中部热带断裂火山多含水层系统与土地利用变化的同位素和离子空间趋势。对泉水和威尔斯井（海拔800至2,400米）进行采样，以测定NO3−和Cl−浓度、δ 18 O水、δ 15 NNO 3和δ 18 ONO 3。贝叶斯同位素混合模型被用来估计潜在的源贡献地下水中的硝酸盐遗产。利用1979年至2019年的卫星图像评估了土地利用变化。据报道，在森林保护区附近的水源泉水中，硝酸盐浓度较低（<1 mg/L NO3−N），而在威尔斯（无限制单元中的中海拔和低海拔地点）和低海拔泉水中，硝酸盐浓度较高（高达1.63 mg/L）。高海拔泉水的特征是Cl−和NO3−/Cl−比值较低，表明土壤氮（SN）输入的潜在影响。威尔斯和低海拔泉水的NO3−/Cl−比值和Cl−浓度高于100 μmol/L。贝叶斯计算表明，污水（家庭化粪池），SN（森林补给区）和化肥（咖啡种植园）的混合物，作为在过去40年中突然的土地利用变化的直接结果。我们的研究结果证实了地下水氮增加的初期趋势，并强调迫切需要一个多城市计划，从国内化粪池过渡到区域污水处理和可持续农业实践，以有效防止未来地下水质量退化。
Nitrate legacy is affecting groundwater sources across the tropics. This study describes isotopic and ionic spatial trends across a tropical, fractured, volcanic multi‐aquifer system in central Costa Rica in relation to land use change over four decades. Springs and wells (from 800 to 2,400 m asl) were sampled for NO3− and Cl− concentrations, δ18Owater, δ15NNO3, and δ18ONO3. A Bayesian isotope mixing model was used to estimate potential source contributions to the nitrate legacy in groundwater. Land use change was evaluated using satellite imagery from 1979 to 2019. The lower nitrate concentrations (<1 mg/L NO3−N) were reported in headwater springs near protected forested areas, while greater concentrations (up to ∼63 mg/L) were reported in wells (mid‐ and low‐elevation sites in the unconfined unit) and low‐elevation springs. High‐elevation springs were characterized by low Cl− and moderate NO3−/Cl− ratios, indicating the potential influence of soil nitrogen (SN) inputs. Wells and low‐elevation springs exhibited greater NO3−/Cl− ratios and Cl− concentrations above 100 μmol/L. Bayesian calculations suggest a mixture of sewage (domestic septic tanks), SN (forested recharge areas), and chemical fertilizers (coffee plantations), as a direct result of abrupt land use change in the last 40 years. Our results confirm the incipient trend in increasing groundwater nitrogen and highlight the urgent need for a multi‐municipal plan to transition from domestic septic tanks to regional sewage treatment and sustainable agricultural practices to prevent future groundwater quality degradation effectively.