Department of Civil Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-6105, United States; Department of Civil Engineering, Chulachomklao Royal Military Academy, Nakhon Nayok 26001, Thailand.
Water Sciences Laboratory, University of Nebraska, Lincoln, NE 68583, United States.
J Contam Hydrol. 2019 Jan;220:33-48. doi: 10.1016/j.jconhyd.2018.11.007. Epub 2018 Nov 22.
A four-decade dataset (1974-2013) of 107,823 nitrate samples in 25,993 wells from western and eastern parts of Nebraska was used to assess long-term trends of groundwater nitrate concentration and decadal changes in the extent of groundwater nitrate-contaminated areas (NO-N ≥ 10 mg N/L) over the entire state. Spatial statistics and regressions were used to investigate the relationships between groundwater nitrate concentrations and several potential natural and anthropogenic factors, including soil drainage capacities, vadose zone characteristics, crop production areas, and irrigation systems. The results of this study show that there is no statistically significant trend in groundwater nitrate concentrations in western Nebraska, in contrast with the increasing trend (p < .05) to the east. The spatial extent and nitrate concentrations in contaminated groundwater in center pivot-irrigated areas was less than in gravity-irrigated areas. Areas with a thicker vadose zone and larger saturated thickness of the aquifer have relatively lower nitrate concentrations. The results of a classification and regression tree (CART) model indicate the difference in the influence of physical factors on groundwater nitrate concentrations between western and eastern Nebraska, namely that groundwater nitrate concentrations correspond with vadose zone thickness, effective hydraulic conductivity, and saturated thickness in the west, while in eastern Nebraska, concentrations are correlated with average percent sand in the topsoil (0-150 cm), well depth, and effective hydraulic conductivity.
利用内布拉斯加州西部和东部 25993 口井的 107823 个硝酸盐样本，长达 40 年的数据（1974-2013 年），评估了整个州地下水硝酸盐浓度的长期趋势和地下水硝酸盐污染区（NO-N≥10mgN/L）的年代际变化。空间统计和回归用于研究地下水硝酸盐浓度与几种潜在的自然和人为因素之间的关系，包括土壤排水能力、包气带特征、作物种植区和灌溉系统。本研究结果表明，内布拉斯加州西部地下水硝酸盐浓度没有统计学上的显著趋势，而东部则呈上升趋势（p<.05）。中心枢轴灌溉区污染地下水的空间范围和硝酸盐浓度小于重力灌溉区。包气带较厚和含水层饱和厚度较大的地区硝酸盐浓度相对较低。分类回归树（CART）模型的结果表明，物理因素对地下水硝酸盐浓度的影响在内布拉斯加州西部和东部存在差异，即地下水硝酸盐浓度与包气带厚度、有效水力传导率和含水层饱和厚度呈正相关，而在东部内布拉斯加州，浓度与表层土壤（0-150cm）中的平均砂百分比、井深和有效水力传导率呈正相关。
