Environmental Science and Policy, Framingham State University, Framingham, MA 01701.
Dept. of Biology, Framingham State University, Framingham, MA 01701.
Water Res. 2021 Sep 1;202:117434. doi: 10.1016/j.watres.2021.117434. Epub 2021 Jul 15.
Despite massive financial investment in mitigation, eutrophication remains a major water quality problem and management priority. Eutrophication science-well established for lakes-is not as well developed for rivers, and scientific understanding of how rivers respond to eutrophication management is far more limited. Long-term data are required to evaluate progress, but such datasets are relatively rare for rivers. We analyzed 23 years of water quality data for the Charles River, a major urban river system in the northeastern U.S.A., to examine nutrient and phytoplankton biomass (chl-a) responses to decades of phosphorus (P) management. Using the more novel and robust approach of quantile regression, we identified statistically and ecologically significant declines in both total phosphorus (TP) and chl-a over time, but only for middle percentiles. Statistically high concentrations of TP and chl-a persist-the segments of the data of greatest concern to managers and the public-and yet this critical result is concealed by statistical tests often employed in eutrophication studies that only evaluate mean changes. TP, temperature, precipitation, and river segment jointly explain the most chl-a variation observed at the decadal scale. Spatial variation is also considerable: despite a significant decline in TP, the impounded lower river exhibits no long-term trend in chl-a and continues to experience annual blooms of harmful cyanobacteria-a lagging response comparable to that of a recovering eutrophic lake. Despite long-term successes in reducing P, chl-a, and cyanobacteria in the Charles River system, we did not detect any significant, long-term change in the attainment of statutory compliance, illustrating the protracted and complex nature of the river's response. Our analysis demonstrates the need for high-frequency, long-term water quality data to evaluate the progress of eutrophication management in urban rivers, and the utility of quantile regression for detecting critical trends in the occurrence of statistically low-frequency but ecologically high-impact events, including blooms of harmful cyanobacteria.
尽管在缓解方面投入了大量资金，但富营养化仍然是一个主要的水质问题和管理重点。湖泊富营养化科学已经得到很好的确立，但河流富营养化科学的发展还不够完善，对河流如何应对富营养化管理的科学理解更是有限。需要长期数据来评估进展，但河流的此类数据集相对较少。我们分析了美国东北部主要城市河流系统查尔斯河 23 年的水质数据，以研究几十年的磷（P）管理对营养物和浮游植物生物量（chl-a）的响应。我们使用更新颖和稳健的分位数回归方法，确定了总磷（TP）和 chl-a 随时间的统计学和生态学上显著下降，但仅适用于中间百分位。TP 和 chl-a 的统计学高浓度仍然存在——这是管理者和公众最关心的数据部分——但这一关键结果被富营养化研究中经常使用的统计测试所掩盖，这些测试仅评估平均变化。TP、温度、降水和河流段共同解释了在十年尺度上观察到的大部分 chl-a 变化。空间变化也相当大：尽管 TP 显著下降，但被堤坝阻挡的下游河流在 chl-a 方面没有长期趋势，并且仍然每年都会发生有害蓝藻的水华——这种滞后反应与恢复富营养化湖泊的反应相当。尽管查尔斯河流域系统在长期减少 P、chl-a 和蓝藻方面取得了成功，但我们没有检测到法定合规性的任何显著、长期变化，这说明了河流响应的漫长而复杂性质。我们的分析表明，需要高频、长期的水质数据来评估城市河流富营养化管理的进展情况，以及分位数回归在检测统计学低频但生态高影响事件（包括有害蓝藻水华）发生的关键趋势方面的效用。
