River network travel time is correlated with dissolved organic matter composition in rivers of the contiguous United States
River network travel time is correlated with dissolved organic matter composition in rivers of the contiguous United States
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DOI：
10.1002/hyp.14124
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发表时间：
2021-03
影响因子：
3.2
通讯作者：
J. Hosen;G. Allen;Giuseppe Amatuli;Sara E. Breitmeyer;M. Cohen;B. Crump;Yuehan Lu;J. Payet;Brett A. Poulin;A. Stubbins;B. Yoon;P. Raymond
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作者：
J. Hosen;G. Allen;Giuseppe Amatuli;Sara E. Breitmeyer;M. Cohen;B. Crump;Yuehan Lu;J. Payet;Brett A. Poulin;A. Stubbins;B. Yoon;P. Raymond
大多数陆地外来有机物在高流量时通过源头进入河网。在源头，外来输入是大量和可变的，但在具有较大流域的溪流和河流中变得不那么重要。随着异源溶解有机质（DOM）向下游移动，具有异源特征的非芳香族有机质所占比例增加。环境因素如何在大陆范围内控制DOM的这种转换还不太确定。我们假设水在内陆系统（溪流、河流、湖泊和水库）的地表水中花费的时间与DOM组成有关。为了验证这一假设，我们使用已建立的河网尺度关系来预测美国60个河流和河流站点的相对河网流量加权旅行时间（FWTT）（超过10个水年的3090个离散样本）。我们估计了上游网络内湖泊和水库体积对旅行时间的实际贡献。采用紫外、可见吸收光谱和荧光光谱定量测定DOM的组成。在考虑流量、比流量、流域面积和上游河道长度的模型中，FWTT和湖泊和水库体积的组合是DOM组成的最佳整体预测因子。各站点DOM光谱斜率比（R2 = 0.77）和新鲜度指数（R2 = 0.78）增加，254 nm特定紫外吸光度（R2 = 0.68）和腐殖化指数（R2 = 0.44）降低。这表明原生样DOM在FWTT较大的水域中持续占据主导地位。我们认为河流的FWTT可以作为DOM组成从源头到河流连续体的度量。检测到的DOM组成变化的性质表明，这种连续体是由光氧化、生物过程、水文变化的陆地补贴和老化的地下水输入共同驱动的。
Most terrestrial allochthonous organic matter enters river networks through headwater streams during high flow events. In headwaters, allochthonous inputs are substantial and variable, but become less important in streams and rivers with larger watersheds. As allochthonous dissolved organic matter (DOM) moves downstream, the proportion of less aromatic organic matter with autochthonous characteristics increases. How environmental factors converge to control this transformation of DOM at a continental scale is less certain. We hypothesized that the amount of time water has spent travelling through surface waters of inland systems (streams, rivers, lakes, and reservoirs) is correlated to DOM composition. To test this hypothesis, we used established river network scaling relationships to predict relative river network flow‐weighted travel time (FWTT) of water for 60 stream and river sites across the contiguous United States (3090 discrete samples over 10 water years). We estimated lentic contribution to travel times with upstream in‐network lake and reservoir volume. DOM composition was quantified using ultraviolet and visible absorption and fluorescence spectroscopy. A combination of FWTT and lake and reservoir volume was the best overall predictor of DOM composition among models that also incorporated discharge, specific discharge, watershed area, and upstream channel length. DOM spectral slope ratio (R2 = 0.77) and Freshness Index (R2 = 0.78) increased and specific ultraviolet absorbance at 254 nm (R2 = 0.68) and Humification Index (R2 = 0.44) decreased across sites as a function of FWTT and upstream lake volume. This indicates autochthonous‐like DOM becomes continually more dominant in waters with greater FWTT. We assert that river FWTT can be used as a metric of the continuum of DOM composition from headwaters to rivers. The nature of the changes to DOM composition detected suggest this continuum is driven by a combination of photo‐oxidation, biological processes, hydrologically varying terrestrial subsidies, and aged groundwater inputs.