RAPID: Extreme Flooding Mobilized Natural Organic Matter from Forested Wetlands - Implication of Mercury and Carbon Cycling in Coastal Blackwater Rivers

RAPID：极端洪水从森林湿地动员天然有机物质 - 汞和碳循环对沿海黑水河流的影响

• 批准号: 1617040
• 负责人: Alex Chow
• 金额: $ 5万
• 依托单位: Clemson University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-15 至 2017-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1617040&HistoricalAwards=false
• 关键词: RAPID; Extreme; Flooding; Mobilized; Natural

Seasonally flooded, freshwater cypress-tupelo wetlands are commonly found in coastal regions of the southeastern United States, from Texas to North Carolina. These wetlands are the main terrestrial source of natural organic matter (NOM) that causes the yellowish tea-colored water in coastal blackwater rivers such as Waccamaw River in South Carolina (SC). Importantly, the concentration of NOM is highly correlated with concentrations of total mercury and methylated mercury, mediating the bioavailability and transport of mercury in coastal ecosystems. On October 1-5, 2015, the interaction between a stalled extratropical cyclone (nor'easter) and hurricane Joaquin caused torrential rain and extensive flooding in a short period of time in the coast of SC, resulting in a large volume of NOM exported from the forested wetlands into the coastal blackwater rivers. Such large quantity of NOM exports on an unprecedented scale could potentially mobilize relatively stable and recalcitrant pools of mercury and carbon from the forested wetlands into the blackwater rivers. This highly interdisciplinary research will dramatically improve understanding of mercury and carbon biogeochemistry under extreme weather conditions and demonstrate the relationships within the context of ecosystems. This study represents a new and unique collaboration between four investigators with different specialties from three universities including two assistant professors respectively in a minority serving institution and an undergraduate institution. This study will also raise the awareness of the impacts of extreme weather events on low-lying coastal areas in the Southeastern United States. Coastal wetlands are considered as important carbon and mercury sinks. However, extreme weather events under the changing climate could alter the equilibrium status, affecting the stability of carbon and mercury pools in the coastal ecosystems. The goal of this RAPID research is to study the influences of the extreme flooding on carbon and mercury cycles and associated biogeochemical processes in coastal wetlands and blackwater rivers. Specifically, the study will integrate field investigations, controlled field experiments, and hydrological computer modeling to examine carbon and mercury exports, sources, and temporal trends along the hydrograph of the extreme flooding event. The research team has been collecting water samples along the Waccamaw River since Oct 4, 2015, representing the rising limb of the hydrograph. Samples were analyzed for general water quality, dissolved organic carbon, ultraviolet absorbance, nutrients, cations, anions, total mercury, and methylated mercury in the filtered and unfiltered samples. To determine the carbon and mercury budget, a hydrological model will be used to estimate the total water discharge from this flooding event that went into Waccamaw River. The PIs will engage in a transformative research study to assess novel decomposition process routes of terrestrial organic matter in forested wetlands under the influence of extreme flooding event. The PIs contend that the novel method of using stable mercury isotope along the hydrograph of the flooding event, coupled with measurements of dissolved organic matter in water using ultraviolet/visible and fluorescence spectroscopy, will be useful for understanding the relationships between carbon and mercury in coastal blackwater rivers. Determining the temporal variation of carbon and mercury will be useful for developing a mechanistic and landscape-level understanding of how extreme flooding events affect the biogeochemical process of terrestrial organic matter in coastal ecosystems.

季节性洪水泛滥的淡水柏树-图珀洛湿地常见于美国东南部沿海地区，从德克萨斯州到北卡罗来纳州。这些湿地是天然有机物 (NOM) 的主要陆地来源，导致南卡罗来纳州 (SC) 的瓦卡莫河 (Waccamaw River) 等沿海黑水河流的水呈茶黄色。重要的是，NOM 的浓度与总汞和甲基化汞的浓度高度相关，调节沿海生态系统中汞的生物利用度和运输。 2015年10月1-5日，停滞的温带气旋（东北）与飓风华金相互作用，在南卡罗来纳州海岸短时间内引发暴雨和大面积洪水，导致南卡罗来纳州大量NOM出口。森林湿地流入沿海黑水河流。以前所未有的规模如此大量的 NOM 出口可能会将相对稳定且顽固的汞和碳库从森林湿地转移到黑水河流中。这项高度跨学科的研究将极大地提高对极端天气条件下汞和碳生物地球化学的理解，并展示生态系统背景下的关系。这项研究代表了来自三所大学的四名不同专业的研究人员之间新的、独特的合作，其中包括分别在少数族裔服务机构和本科院校的两名助理教授。这项研究还将提高人们对极端天气事件对美国东南部低洼沿海地区影响的认识。沿海湿地被认为是重要的碳汇和汞汇。然而，气候变化下的极端天气事件可能会改变平衡状态，影响沿海生态系统碳库和汞库的稳定性。这项 RAPID 研究的目标是研究极端洪水对沿海湿地和黑水河流中碳和汞循环以及相关生物地球化学过程的影响。具体来说，该研究将整合实地调查、受控实地实验和水文计算机建模，以检查极端洪水事件沿水文过程线的碳和汞输出、来源和时间趋势。自 2015 年 10 月 4 日以来，研究小组一直在瓦卡莫河沿岸采集水样，代表水文上升部分。对过滤和未过滤样品中的一般水质、溶解有机碳、紫外线吸光度、营养物、阳离子、阴离子、总汞和甲基化汞进行分析。为了确定碳和汞预算，将使用水文模型来估算本次洪水事件流入瓦卡莫河的总排水量。项目负责人将开展一项变革性研究，以评估极端洪水事件影响下森林湿地陆地有机物的新分解过程路线。 PI 认为，沿洪水事件过程线使用稳定汞同位素的新方法，再加上使用紫外/可见光和荧光光谱测量水中溶解的有机物，将有助于了解沿海地区碳和汞之间的关系。黑水河。确定碳和汞的时间变化将有助于从机制和景观层面理解极端洪水事件如何影响沿海生态系统中陆地有机物的生物地球化学过程。