Abstract

Changes in groundwater chemistry in the Great Bend Prairie aquifer, a portion of the High Plains aquifer in south-central Kansas (USA), were studied in order to better understand factors influencing groundwater quality and aquifer sustainability. To assess changes, groundwater samples from 22 monitoring wells were analyzed during 2016. Results were then compared to data obtained previously from the same wells in the 1970s and 1980s. Of the wells sampled, 13 wells were screened near the water table (average depth 22 m) and 9 wells were screened near the aquifer base (average depth 41 m). Nitrate levels in 2016 were higher for 20 of 21 wells with data available for comparison. The average increase for shallow-aquifer and aquifer-base samples was 9.5 (standard deviation, SD, 12.9) and 3.4 (SD 3.1) mg/L as N, respectively. Nitrate isotope ratios (δ¹⁵N-NO₃ and δ¹⁸O-NO₃) of the 2016 samples are consistent with nitrification of ammonium-based fertilizers as the nitrate source with potential contributions from animal waste. Total dissolved solute levels were also higher in samples from nine of 12 shallow-aquifer wells and four of eight aquifer-base wells, with average increases of 191 (SD 238) and 194 (SD 133) mg/L, respectively. Taken together, the results demonstrate that water quality has decreased considerably over the past 40 years primarily because of fertilizer use, but that groundwater mixing, evapotranspiration, and potentially animal waste inputs also affected groundwater chemistry. These findings help identify the scale of water-quality degradation in the High Plains aquifer.

中文翻译：

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美国堪萨斯州中南部高平原含水层的地下水地球化学的长期变化（1970-2016年）

摘要

为了更好地了解影响地下水质量和含水层可持续性的因素，研究了大弯本草原含水层（美国堪萨斯州中南部的高平原含水层的一部分）中的地下水化学变化。为了评估变化，2016年对22口监测井的地下水样品进行了分析。然后将结果与先前从1970年代和1980年代从同一口井获得的数据进行了比较。在取样的所有井中，在地下水位附近筛查了13口井（平均深度22 m），在含水层底部附近筛查了9口井（平均深度41 m）。可比较的数据显示，2016年21口井中的20口硝酸盐水平较高。浅层含水层和以含水层为基础的样品的平均增加量分别为9.5（标准差，SD，12.9）和3.4（SD 3.1）mg / L（N）。硝酸盐同位素比（δ¹⁵ N-NO ₃和δ ¹⁸ O型NO ₃的2016个样本）是具有基于铵的肥料作为硝酸盐源与从动物废物的潜在贡献的硝化是一致的。12个浅层含水井中的9个井和8个含水层基井中的4个井中的样品中的总溶解溶质水平也较高，分别平均增加191（SD 238）和194（SD 133）mg / L。两者合计，结果表明，过去40年水质已显着下降，主要原因是使用化肥，但是地下水的混合，蒸散和潜在的动物废物输入也影响了地下水的化学性质。这些发现有助于确定高平原含水层中水质退化的程度。