Exploring Silica Stoichiometry on a Large Floodplain Riverscape
Exploring Silica Stoichiometry on a Large Floodplain Riverscape
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DOI：
10.3389/fevo.2019.00346
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发表时间：
2019-09
影响因子：
3
通讯作者：
J. Carey;K. Jankowski;Paul Julian;L. Sethna;Patrick K. Thomas;Jason J. Rohweder
中科院分区：
文献类型：
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作者：
J. Carey;K. Jankowski;Paul Julian;L. Sethna;Patrick K. Thomas;Jason J. Rohweder
淡水生态系统是陆地 - 海洋连续体中营养物质和碳（C）处理的关键区域。相对于我们对淡水系统内碳（C）、氮（N）和磷（P）循环的了解，对硅（Si）循环和输出的控制了解较少。河流向沿海受纳水体输出的硅（Si）相对于氮（N）和磷（P）的量能够决定浮游植物的种类组合，进而影响碳循环和食物网结构。在此，我们利用两个数据集（一个来自支流，一个来自干流）研究了溶解硅（DSi）、总氮（TN）和总磷（TP）浓度之间的关系，以及这些关系如何与密西西比河上游水系（UMRS）的流域土地覆盖、岩性和河流水文地貌（即不同的“水域”之间）相关联。这两个数据集涵盖了九年时间（2010 - 2018年），代表了超过10,000个独特样本。我们发现，在干流UMRS的南北梯度上，所有六种水域类型的DSi浓度以及Si:TP和Si:TN比值都显著下降。这一信号部分是由沿此纬度梯度的支流DSi输入相应减少所驱动的。与北美其他地区的研究结果相反，流域土地覆盖不是支流DSi浓度的重要预测因子，尤其是与岩性相比。然而，Si:TN和Si:TP比值似乎受到流域土地覆盖的强烈控制，这可能是由于行栽作物农业带来的过量氮（N）和磷（P）负荷。硅（Si）及其与氮（N）和磷（P）的比值（即硅化学计量比）在大多数水域类型中相似，包括径流式水库和主河道，这表明在这些河段影响硅（Si）、氮（N）和磷（P）浓度的过程相似。然而，与其他水域类型相比，回水湖的DSi和TN浓度较低，这凸显了水停留时间和养分吸收在控制内陆水体硅化学计量比方面的重要性。总之，我们的研究结果表明，河流不是硅的简单通道，而是流域特征、水文和生物吸收的复杂性导致了河流连续体中动态的硅化学计量比。
Freshwater ecosystems are critical zones of nutrient and carbon (C) processing along the land-sea continuum. Relative to our understanding of C, nitrogen (N), and phosphorus (P) cycling within the freshwater systems, the controls on silicon (Si) cycling and export are less understood. The amount of Si in relation to N and P exported by rivers to coastal receiving waters can determine phytoplankton species assemblages, which in turn affects C cycling and food web structure. Here we examine the relationships between dissolved Si (DSi), total nitrogen (TN), and total phosphorus (TP) concentrations, and how these relationships relate to basin land cover, lithology, and river hydrogeomorphology (i.e., among different ‘aquatic areas’) in the Upper Mississippi River System (UMRS) using two datasets (one from the tributaries and one from the mainstem) that span a nine-year period (2010-2018) representing >10,000 unique samples. We found significant declines in DSi concentrations, as well as Si:TP and Si:TN ratios along the north-south gradient of the mainstem UMRS across all six aquatic area types. This signal was driven partially by a corresponding decline in tributary DSi inputs along this latitudinal gradient. Contrary to findings from other regions of North America, basin land cover was not an important predictor of tributary DSi concentrations, especially compared to lithology. However, Si:TN and Si:TP ratios appear to be strongly controlled by basin land cover, likely due to excess N and P loading from row-crop agriculture. Si, and its ratio with N and P (i.e., Si stoichiometry), was similar across most aquatic area types, including run-of-river impoundments and the main channel, suggesting similar processes affecting Si, N, and P concentrations in these reaches. However, backwater lakes had lower DSi and TN concentrations and compared to the other aquatic area types, highlighting the importance of water residence time and nutrient uptake in controlling Si stoichiometry in inland waters. Together, our results show rivers are not simple pipes for Si, but rather the complexity in watershed characteristics, hydrology, and biological uptake results in dynamic Si stoichiometry along the river continuum.