Murdoch Peter S, Shanley James B
US Geological Survey, Troy, NY, USA.
Environ Monit Assess. 2006 Sep;120(1-3):1-25. doi: 10.1007/s10661-005-9028-1. Epub 2006 Aug 1.
Two new methods for assessing temporal trends in stream-solute concentrations at specific streamflow ranges were applied to long (40 to 50-year) but sparse (bi-weekly to quarterly sampling) stream-water quality data collected at three forested mesoscale basins along an atmospheric deposition gradient in the northeastern United States (one in north-central Pennsylvania, one in southeastern New York, and one in eastern Maine). The three data sets span the period since the implementation of the Clean Air Act in 1970 and its subsequent amendments. Declining sulfate (O4(2-)) trends since the mid 1960s were identified for all 3 rivers by one or more of the 4 methods of trend detection used. Flow-specific trends were assessed by segmenting the data sets into 3-year and 6-year blocks, then determining concentration-discharge relationships for each block. Declining sulfate (O4(2-)) trends at median flow were similar to trends determined using a Seasonal Kendall Tau test and Sen slope estimator. The trend of declining O4(2-) concentrations differed at high, median and low flow since the mid 1980s at YWC and NR, and at high and low flow at WR, but the trends leveled or reversed at high flow from 1999 through 2002. Trends for the period of record at high flows were similar to medium- and low-flow trends for Ca2++ Mg2+ concentrations at WR, non-significant at YWC, and were more negative at low flow than at high flow at NR; trends in nitrate (NO3-), and alkalinity (ALK) concentrations were different at different flow conditions, and in ways that are consistent with the hydrology and deposition history at each watershed. Quarterly sampling is adequate for assessing average-flow trends in the chemical parameters assessed over long time periods (approximately decades). However, with even a modest effort at sampling a range of flow conditions within each year, trends at specified flows for constituents with strong concentration-discharge relationships can be evaluated and may allow early detection of ecosystem response to climate change and pollution management strategies.
两种用于评估特定流量范围内河流溶质浓度时间趋势的新方法，被应用于美国东北部沿大气沉降梯度的三个森林中尺度流域收集的长期（40至50年）但稀疏（每两周至每季度采样）的河流水质数据（一个位于宾夕法尼亚州中北部，一个位于纽约州东南部，一个位于缅因州东部）。这三个数据集涵盖了自1970年《清洁空气法》实施及其后续修正案以来的时间段。通过使用的4种趋势检测方法中的一种或多种，确定了所有3条河流自20世纪60年代中期以来硫酸盐（SO₄²⁻）下降的趋势。通过将数据集分割为3年和6年的时间段，然后确定每个时间段的浓度-流量关系，评估了特定流量趋势。中位流量下硫酸盐（SO₄²⁻）下降趋势与使用季节性肯德尔秩次相关检验和森斜率估计器确定的趋势相似。自20世纪80年代中期以来，在YWC和NR处，高、中、低流量下SO₄²⁻浓度下降趋势不同，在WR处高流量和低流量下也不同，但在1999年至2002年期间高流量趋势趋于平稳或逆转。WR处高流量记录期的趋势与Ca²⁺+Mg²⁺浓度的中、低流量趋势相似，在YWC处不显著，在NR处低流量趋势比高流量趋势更负；硝酸盐（NO₃⁻）和碱度（ALK）浓度趋势在不同流量条件下不同，且与每个流域的水文和沉积历史一致。每季度采样足以评估长期（约几十年）内所评估化学参数的平均流量趋势。然而，即使每年在采样一系列流量条件方面付出适度努力，对于具有强浓度-流量关系的成分，也可以评估特定流量下的趋势，并可能有助于早期检测生态系统对气候变化的响应和污染管理策略。
