Burkart M R, Stoner J D
USDA-ARS, Ames, Iowa 50011, USA.
Water Sci Technol. 2002;45(9):19-28.
Research from several regions of the world provides spatially anecdotal evidence to hypothesize which hydrologic and agricultural factors contribute to groundwater vulnerability to nitrate contamination. Analysis of nationally consistent measurements from the U.S. Geological Survey's NAWOA program confirms these hypotheses for a substantial range of agricultural systems. Shallow unconfined aquifers are most susceptible to nitrate contamination associated with agricultural systems. Alluvial and other unconsolidated aquifers are the most vulnerable and shallow carbonate aquifers provide a substantial but smaller contamination risk. Where any of these aquifers are overlain by permeable soils the risk of contamination is larger. Irrigated systems can compound this vulnerability by increasing leaching facilitated by additional recharge and additional concentrations of groundwater nitrate than all other agricultural systems, although mean nitrate concentrations in counties with dairy, poultry, cattle and grains, and horticulture systems were similar. If trends in the relation between increased fertilizer use and groundwater nitrate in the United States are repeated in other regions of the world, Asia may experience increasing problems because of recent increases in fertilizer use. Groundwater monitoring in Western and Eastern Europe as well as Russia over the next decade may provide data to determine if the trend in increased nitrate contamination can be reversed. If the concentrated livestock trend in the United States is global, it may be accompanied by increasing nitrogen contamination in groundwater. Concentrated livestock provide both point sources in the confinement area and intense non-point sources as fields close to facilities are used for manure disposal. Regions where irrigated cropland is expanding, such as in Asia, may experience the greatest impact of this practice.
来自世界多个地区的研究提供了空间上的轶事证据，以推测哪些水文和农业因素导致地下水易受硝酸盐污染。对美国地质调查局的NAWOA计划全国一致测量数据的分析证实了这些假设适用于广泛的农业系统。浅层无压含水层最容易受到与农业系统相关的硝酸盐污染。冲积含水层和其他松散含水层最易受污染，浅层碳酸盐含水层也存在相当大但较小的污染风险。当这些含水层中的任何一个被渗透性土壤覆盖时，污染风险就会更大。灌溉系统会因额外补给促进淋溶以及地下水硝酸盐浓度高于所有其他农业系统而加剧这种脆弱性，尽管乳制品、家禽、牲畜、谷物和园艺系统所在县的平均硝酸盐浓度相似。如果美国化肥使用增加与地下水硝酸盐之间的关系趋势在世界其他地区重演，亚洲可能会因近期化肥使用增加而面临越来越多的问题。未来十年在西欧、东欧以及俄罗斯进行的地下水监测可能会提供数据，以确定硝酸盐污染增加的趋势是否可以逆转。如果美国集中式畜牧业的趋势是全球性的，可能会伴随着地下水中氮污染的增加。集中式畜牧业在圈养区域提供点源污染，在设施附近的田地用于粪便处理时也提供强烈的非点源污染。灌溉农田正在扩大的地区，如亚洲，可能会受到这种做法的最大影响。
