Dept. of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada.
Dept. of Marine Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27606, United States of America.
Sci Total Environ. 2021 Mar 15;760:143414. doi: 10.1016/j.scitotenv.2020.143414. Epub 2020 Nov 7.
Chromophoric dissolved organic matter (CDOM) exported from riverine catchments can influence biogeochemical processes in coastal environments with implications for water quality and carbon budget. Despite recent efforts to quantify C fluxes during high flow events, knowledge gaps exist regarding the fluxes and yield of terrestrial, reactive vs. recalcitrant CDOM under episodic to base-flow conditions from uplands to downstream estuaries. We used stream dissolved organic carbon (DOC) concentrations and CDOM optical properties using parallel factor analysis to characterize composition and fluxes under variable flow conditions for a coastal river basin in the SE USA. Our findings showed that episodic flows (>75th percentile) were marked by the elevated flux of humic acid-like CDOM and lower in-stream autochthonous production, or microbial degradation. Further, 70% of the terrestrial CDOM was exported during high flows, with a 3-fold increase in CDOM flux during episodic events, including Hurricane Irene in 2011. While, low flows (<25th percentile) were marked by an increased abundance of microbial, humic CDOM that can be easily processed within the estuary. Due to greater wetland coverage in the Neuse, the annual CDOM yield was 5-6 times higher than the larger rivers, such as the Mississippi, USA, and Changjiang, China. We suggest that similar coastal watersheds in SE USA or elsewhere may contribute substantial amounts of reactive CDOM to the estuaries during high flow conditions and can have negative water quality implications for the coastal C dynamics. These findings can help predict the evolution of coastal C cycling under projected climate change and inform the development of appropriate management strategies.
河川流域输出的有色溶解有机物质 (CDOM) 会影响沿海环境中的生物地球化学过程，从而影响水质和碳预算。尽管最近在量化高流量事件期间的碳通量方面做出了努力，但对于从高地到下游河口的间歇性到基流条件下陆地、反应性与难降解 CDOM 的通量和产量，仍存在知识空白。我们使用溪流溶解有机碳 (DOC) 浓度和 CDOM 光学特性，通过平行因子分析来描述美国东南部沿海流域可变流量条件下的组成和通量。我们的研究结果表明，间歇性水流（>第 75 百分位数）的特征是腐殖酸样 CDOM 通量的升高和溪流中自生产量或微生物降解的降低。此外，70%的陆地 CDOM 在高流量时被输出，在间歇性事件期间 CDOM 通量增加了 3 倍，包括 2011 年的飓风艾琳。而低流量（<第 25 百分位数）的特征是微生物、腐殖质 CDOM 的丰度增加，这些 CDOM 很容易在河口内被处理。由于 Neuse 湿地的覆盖面积更大，每年的 CDOM 产量比美国密西西比河和中国长江等更大的河流高出 5-6 倍。我们认为，美国东南部或其他类似的沿海流域在高流量条件下可能会向河口输送大量反应性 CDOM，这对沿海碳动态可能会产生负面的水质影响。这些发现有助于预测在预计的气候变化下沿海碳循环的演变，并为制定适当的管理策略提供信息。
