U.S. Geological Survey, Sacramento, California 95819, USA.
Environ Sci Technol. 2010 Jul 1;44(13):4988-97. doi: 10.1021/es100546y.
An assessment of nitrate concentrations in groundwater in the United States indicates that concentrations are highest in shallow, oxic groundwater beneath areas with high N inputs. During 1991-2003, 5101 wells were sampled in 51 study areas throughout the U.S. as part of the U.S. Geological Survey National Water-Quality Assessment (NAWQA) program. The well networks reflect the existing used resource represented by domestic wells in major aquifers (major aquifer studies), and recently recharged groundwater beneath dominant land-surface activities (land-use studies). Nitrate concentrations were highest in shallow groundwater beneath agricultural land use in areas with well-drained soils and oxic geochemical conditions. Nitrate concentrations were lowest in deep groundwater where groundwater is reduced, or where groundwater is older and hence concentrations reflect historically low N application rates. Classification and regression tree analysis was used to identify the relative importance of N inputs, biogeochemical processes, and physical aquifer properties in explaining nitrate concentrations in groundwater. Factors ranked by reduction in sum of squares indicate that dissolved iron concentrations explained most of the variation in groundwater nitrate concentration, followed by manganese, calcium, farm N fertilizer inputs, percent well-drained soils, and dissolved oxygen. Overall, nitrate concentrations in groundwater are most significantly affected by redox conditions, followed by nonpoint-source N inputs. Other water-quality indicators and physical variables had a secondary influence on nitrate concentrations.
对美国地下水中硝酸盐浓度的评估表明,在高氮输入地区,浅层、含氧地下水中的浓度最高。1991 年至 2003 年,作为美国地质调查局国家水质评估(NAWQA)计划的一部分,在美国 51 个研究区域的 5101 口井中进行了采样。这些井网络反映了主要含水层中国内井所代表的现有利用资源(主要含水层研究),以及主要地表活动(土地利用研究)下最近重新补给的地下水。在土壤排水良好且具有氧化地球化学条件的农业用地的浅层地下水中,硝酸盐浓度最高。在地下水被还原的深层地下水中,或者地下水较老,因此浓度反映了历史上较低的氮施用量,硝酸盐浓度最低。分类和回归树分析用于确定氮输入、生物地球化学过程和物理含水层特性在解释地下水中硝酸盐浓度方面的相对重要性。按平方和减少排序的因素表明,溶解铁浓度解释了地下水硝酸盐浓度变化的大部分,其次是锰、钙、农田氮肥投入、土壤渗透率百分比和溶解氧。总体而言,地下水中的硝酸盐浓度受氧化还原条件的影响最大,其次是非点源氮输入。其他水质指标和物理变量对硝酸盐浓度有次要影响。