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首页> 外文期刊>Estuarine Coastal and Shelf Science >Four decades of water quality change in the upper San Francisco Estuary
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Four decades of water quality change in the upper San Francisco Estuary

机译：旧金山河口上游四十年的水质变化

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Quantitative descriptions of chemical, physical, and biological characteristics of estuaries are critical for developing an ecological understanding of drivers of change. Historical trends and relationships between key species of dissolved inorganic nitrogen (ammonium, nitrateitrite, total) from the Delta region of the San Francisco Estuary were modelled with an estuarine adaptation of the Weighted Regressions on Time, Discharge, and Season (WRTDS). Analysis of flow-normalized data revealed trends that were different from those in the observed time-series. Flow-normalized data exhibited changes in magnitude and even reversal of trends relative to the observed data. Modelled trends demonstrated that nutrient concentrations were on average higher in the last twenty years relative to the earlier periods of observation, although concentrations have been slowly declining since the mid-1990s and early 2000s. We further describe mechanisms of change with two case studies that evaluated 1) downstream changes in nitrogen following upgrades at a wastewater treatment plant, and 2) interactions between biological invaders, chlorophyll, macro-nutrients (nitrogen and silica), and flow in Suisun Bay. WRTDS results for ammonium trends showed a distinct signal as a result of upstream wastewater treatment plant upgrades, with specific reductions observed in the winter months during low-flow conditions. Results for Suisun Bay showed that chlorophyll a production in early years was directly stimulated by flow, whereas the relationship with flow in later years was indirect and influenced by grazing pressure. Although these trends and potential causes of change have been described in the literature, results from WRTDS provided an approach to test alternative hypotheses of spatiotemporal drivers of nutrient dynamics in the Delta.
机译：定量描述河口的化学，物理和生物学特性对于建立对变化驱动因素的生态理解至关重要。利用趋势，时间，流量和季节加权回归（WRTDS）的河口模型，对来自旧金山河口三角洲地区的溶解无机氮的关键物种（铵，硝酸盐/亚硝酸盐，总量）的历史趋势和关系进行了建模。对流量归一化数据的分析显示出与观察到的时间序列不同的趋势。相对于观测数据，流量归一化数据表现出幅度的变化，甚至趋势的逆转。模拟趋势表明，尽管从1990年代中期和2000年代初以来，营养素的浓度一直在缓慢下降，但在过去20年中，其营养素的平均浓度要高于早期的观测。我们通过两个案例研究进一步描述了变化的机制，该案例评估了1）废水处理厂升级后下游氮素的变化，以及2）生物入侵者，叶绿素，大量养分（氮和二氧化硅）与穗顺湾水流之间的相互作用。铵趋势的WRTDS结果显示出上游废水处理厂升级的明显信号，在冬季低流量条件下观察到特定的减少。遂孙湾的研究结果表明，水流直接刺激了早年叶绿素a的产生，而晚年与水流的关系是间接的，并且受到放牧压力的影响。尽管这些趋势和潜在的变化原因已在文献中进行了描述，但WRTDS的结果提供了一种方法来检验三角洲营养动态时空驱动因素的替代假设。

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