In calcareous watersheds, groundwater alkalinity results largely from dissolution of carbonate minerals in soils. The alkalinity increases initially approximately in proportion to nitrate (NO 3 − ) concentration and eventually approaches an apparent maximum of approximately 8 mmol L −1 at high NO 3 − concentrations. This close positive relationship between alkalinity and NO 3 − concentration appears to be predominantly a result of three processes: (i) mineralization of organic nitrogen fertilizer, (ii) exchange of OH − and H + during the uptake of NO 3 − or ammonium by crop plants, and (iii) CO 2 released by roots as a result of fertilizer-stimulated plant growth. We suggest that the asymptotic approach to a maximum groundwater alkalinity at NO 3 − concentrations exceeding 0.25 mmol L −1 may be caused by (i) a maximum possible areal crop production at excessive N fertilization and (ii) an increasing CO 2 loss to the atmosphere due to the increasing CO 2 production in the soil. Our analysis provides a general understanding and quantitative prediction of steady-state groundwater NO 3 − concentration, alkalinity, pH, the degree of CO 2 supersaturation in the soil, and soil CO 2 emissions to the atmosphere. The positive correlation between alkalinity and NO 3 − concentration observed in groundwaters persists in rivers and lakes. We conclude that an economically efficient agricultural practice that avoids over-fertilization might accelerate the in-soil carbonate weathering rate up to approximately threefold compared to unfertilized soils, but it will not jeopardize the use of aquifers for drinking water.

中文翻译：

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土壤施氮促进钙质流域碳酸盐风化和易位

在钙质流域，地下水碱度主要是由碳酸盐矿物在土壤中溶解造成的。碱度最初大约与硝酸盐(NO 3 - ) 浓度成比例地增加，并且最终在高NO 3 - 浓度下接近大约8 mmol L -1 的表观最大值。碱度和 NO 3 - 浓度之间的这种密切正相关似乎主要是三个过程的结果：(i) 有机氮肥的矿化，(ii) 在吸收 NO 3 - 或铵的过程中交换 OH - 和 H +作物植物，以及 (iii) 由于肥料刺激植物生长而由根部释放的 CO 2。我们建议在 NO 3 - 浓度超过 0 时对最大地下水碱度的渐近方法。25 mmol L -1 可能由以下原因引起：(i)过量施氮时最大可能的面积作物产量和(ii)由于土壤中CO 2 产量增加而导致的CO 2 损失增加到大气中。我们的分析提供了对稳态地下水 NO 3 - 浓度、碱度、pH、土壤中 CO 2 过饱和度以及土壤向大气排放的 CO 2 的一般理解和定量预测。在地下水中观察到的碱度和NO 3 - 浓度之间的正相关在河流和湖泊中持续存在。我们得出的结论是，与未施肥的土壤相比，避免过度施肥的经济有效的农业实践可能会将土壤碳酸盐风化速率加快约三倍，但不会危及含水层作为饮用水的使用。