McIsaac G F, Libra R D
Department of Natural Resources and Environmental Sciences, University of Illinois, W-503 Turner Hall, 1102 South Goodwin Avenue, Urbana, IL 61801, USA.
J Environ Qual. 2003 Nov-Dec;32(6):2280-9. doi: 10.2134/jeq2003.2280.
Recent compilations of historical and contemporary riverine nitrate (NO3) concentrations indicate that concentrations in many rivers in the north-central USA increased during the second half of the 20th century. The Des Moines River near Des Moines, Iowa, however, was reported to have had similar NO3 concentrations in 1945 and the 1980s, in spite of substantially greater N input to the watershed during the latter period. The objective of this study was to reconsider the comparison of historical and contemporary NO3 concentrations in the Des Moines River near Des Moines in light of the following: (i) possible errors in the historical data used, (ii) variations in methods of sample collection, (iii) variations in location of sampling, and (iv) additional data collected since 1990. We discovered that an earlier study had compared the flow-weighted average concentration in 1945 to arithmetic annual average concentrations in the 1980s. The intertemporal comparison also appeared to be influenced by differences in sample collection methods and locations used at different times. Depending on the model used and the estimated effects of composite sample collection, the 1945 arithmetic average NO3 concentration was between 44 and 57% of the expected mean value at a similar water yield during 1976-2001. The flow-weighted average NO3 concentration for 1945 was between 54 and 73% of the expected mean value at a similar water yield during 1976-2001. The difference between NO3 concentrations in 1945 and the contemporary period are larger than previously reported for the Des Moines River.
近期对历史和当代河流硝酸盐（NO₃）浓度的汇编表明，美国中北部许多河流的浓度在20世纪后半叶有所增加。然而，据报道，爱荷华州得梅因附近的得梅因河在1945年和20世纪80年代的NO₃浓度相似，尽管后期流域的氮输入大幅增加。本研究的目的是根据以下因素重新考虑得梅因附近得梅因河历史和当代NO₃浓度的比较：（i）所用历史数据可能存在的误差，（ii）样本采集方法的变化，（iii）采样地点的变化，以及（iv）1990年以来收集的额外数据。我们发现，早期一项研究将1945年的流量加权平均浓度与20世纪80年代的算术年均浓度进行了比较。跨期比较似乎也受到不同时期样本采集方法和地点差异的影响。根据所使用的模型以及复合样本采集的估计影响，1945年的算术平均NO₃浓度在1976 - 2001年类似产水量时预期平均值的44%至57%之间。1945年的流量加权平均NO₃浓度在1976 - 2001年类似产水量时预期平均值的54%至73%之间。1945年与当代时期的NO₃浓度差异比之前报道的得梅因河的差异更大。
