US Geological Survey, Denver Federal Center, Box 25046 MS 415, Denver, Colorado 80225, United States.
Environ Sci Technol. 2011 Sep 1;45(17):7209-16. doi: 10.1021/es201221s. Epub 2011 Aug 9.
Changes in nitrate concentration and flux between 1980 and 2008 at eight sites in the Mississippi River basin were determined using a new statistical method that accommodates evolving nitrate behavior over time and produces flow-normalized estimates of nitrate concentration and flux that are independent of random variations in streamflow. The results show that little consistent progress has been made in reducing riverine nitrate since 1980, and that flow-normalized concentration and flux are increasing in some areas. Flow-normalized nitrate concentration and flux increased between 9 and 76% at four sites on the Mississippi River and a tributary site on the Missouri River, but changed very little at tributary sites on the Ohio, Iowa, and Illinois Rivers. Increases in flow-normalized concentration and flux at the Mississippi River at Clinton and Missouri River at Hermann were more than three times larger than at any other site. The increases at these two sites contributed much of the 9% increase in flow-normalized nitrate flux leaving the Mississippi River basin. At most sites, concentrations increased more at low and moderate streamflows than at high streamflows, suggesting that increasing groundwater concentrations are having an effect on river concentrations.
利用一种新的统计方法，确定了 1980 年至 2008 年密西西比河流域 8 个地点硝酸盐浓度和通量的变化情况。该方法能够适应硝酸盐随时间的演变，产生与流量无关的、归一化的硝酸盐浓度和通量估计值，不受流量随机变化的影响。结果表明，自 1980 年以来，减少河流硝酸盐方面几乎没有取得一致的进展，一些地区的归一化浓度和通量呈上升趋势。在密西西比河和密苏里河的四个支流以及俄亥俄河、爱荷华河和伊利诺伊河的支流上，有四个地点的归一化硝酸盐浓度和通量增加了 9%至 76%，而在其他支流上变化很小。在密西西比河的克林顿和密苏里河的赫尔曼，归一化浓度和通量的增加幅度比其他任何地点都要大三倍以上。这两个地点的增加导致密西西比河流域归一化硝酸盐通量增加了 9%。在大多数地点，低流量和中流量的浓度增加幅度大于高流量，表明地下水浓度的增加正在影响河流浓度。
