RAPID: Cascading of Extreme Events (Drought-Wildfire) in a Pristine Watershed Located in the Southeast US: Implication on Hydrology, Water Quality and Microbial Communities

美国东南部许多地区正处于极端干旱之中，这不仅威胁到我们的农业生产力，还可能导致森林火灾，并引发其他连锁事件。其中一个事件就是对饮用水质量的影响。南卡罗来纳州格林维尔的大部分饮用水来自一个保护良好的水库，该水库位于森林中央，目前正在进行的森林大火严重破坏了这座水库，这场大火在过去一周刚刚得到控制。随着随之而来的季节性降雨，许多焚烧的材料将进入向这个大城市供水的溪流。我们在这个项目中的目的是了解森林大火对这个重要水库的水文和水质造成的变化。我们将比较受火灾影响的溪流和未受影响的溪流之间的水文、生物和化学差异，以评估这些极端事件是否会影响我们的饮用水质量。我们将结合新的水文模型和下一代分子工具与标准的化学测量来研究这些差异。一名帮助开发水文模型的工程学研究生也将接受这些最新微生物学和统计技术的交叉培训。我们的评估将是了解森林火灾可能对美国其他地区的水质产生什么影响的重要一步。该项目的目标是收集与易腐烂的水质有关的数据，以确定当前极端气候(如干旱和随后的野火事件)如何影响南卡罗来纳州原始分水岭的水文、水质以及微生物群落的组成和结构。具体地说，我们将解决以下问题：a)火灾发生后，分水岭内的水质如何变化？与河流内部过程的变化相比，流域条件的变化(地形变化和水文变化)在多大程度上控制了水质的变化？和b)我们将根据火灾前和火灾后的情况，具体评估干旱-野火对原始流域的径流和泥沙负荷的影响。我们将评估野火对溪流水质的影响，例如溶解氧、硝酸盐、磷酸盐、重金属和铵；分类群丰富度(α多样性)和微生物群落的结构和组成。我们将利用下一代测序来评估微生物群落，并在统计上比较通过这些分子和化学分析评估的水质与未受森林火灾影响的溪流的差异。通过这些实验，我们希望量化火灾后水质的主要控制以及减轻溪流水质的内部溪流过程。这些数据将使溪流水质恢复时间得到更好的描述，并将直接影响火灾后分水岭作为公共供水应如何管理。这项研究将告知利益攸关方(例如，格林维尔水系)野火可能对水质造成的影响，并采取必要的措施，如绿色技术，帮助减少来自流域烧毁区域的任何碎片径流和/或任何溪流淤积。这些研究结果可以应用于美国其他地区，因为目前和预计未来将发生干旱和野火事件。

Many parts of the southeastern US are in the middle of an extreme drought that not only threatens our agricultural productivity, but also may lead to forest fires that have other cascading events. One such event is the impact on drinking water quality. Greenville, SC obtains the bulk of its drinking water from a well-protected reservoir that is situated in the middle of a forest that is currently heavily damaged by ongoing forest fires that just got under control within the past week. With the ensuing seasonal rains, much of the burned material will enter the streams that supply water to this large, metropolitan city. Our aims in this project are to access the changes that the forest fire has on the hydrology and water quality of this important reservoir. We will compare hydrological, biological and chemical differences between streams impacted by fire and those that have not been impacted to evaluate if these extreme events affect the quality of our drinking water. We will combine new hydrological models and next generation molecular tools with standard chemical measurements to investigate these differences. An engineering graduate student that is helping to develop the hydrological model will also be cross-trained in these latest microbiological and statistical techniques. Our assessment will be an important step in understanding what impacts forest fires may have on water quality in other areas of the US. The objective of this project is to collect perishable water quality related data to determine how the current combination of climate extremes such as droughts and subsequent wildfire events affect a pristine watershed in South Carolina in terms of its hydrology, water quality, and microbial community composition and structure. Specifically, we will address the following:a) How does the water quality change within a watershed following fire? How much water quality change is controlled by change in watershed conditions (altered landscape and changing hydrology) vs changes in stream internal processes? andb) We will evaluate the consequences of drought - wildfire regime specifically after the destruction of the vegetation cover and the subsequent alteration of spatial soil properties (e.g., infiltration) and geomorphic features on runoff and sediment loads in a pristine watershed based on the pre-fire and the post-fire conditions.We will assess the influence of wildfires on stream water quality, for example, dissolved oxygen, nitrate, phosphate, heavy metals and ammonium; taxon richness (alpha diversity) and the structure and composition of microbial communities. We will utilize next-generation sequencing to assess the microbial communities and statistically compare differences in water quality as assessed by these molecular and chemical assays to streams not impacted by forest fires. With these experiments we hope to quantify the major controls on post-fire water quality as well as the internal stream processes that mitigate stream water quality. These data will enable stream water quality recovery times to be better characterized and will directly impact how the post-fire watershed should be managed as a public water supply. This research will inform stakeholders (e.g., Greenville water system) about the possible impacts of wildfire on water quality and take necessary steps such as green technology to help mitigate any debris run-off and/or any stream siltation from the burned areas of the watershed. These research findings can be applied to other areas of the U.S. due to current and expected future combinations of drought and wildfire events.