Collaborative Research: Water partitioning between trees, soils, and streams following forest disturbance

在毗连的美国，超过一半的淡水供应来自森林流域。因此，至关重要的是，必须妥善管理有森林覆盖的水源集水区，以确保为水生生态系统和下游社区提供清洁和充足的水。造林试验流域的研究表明，减少森林覆盖一般会增加出水量，而造林则会减少出水量。但是，对于流量变化的幅度和持久性，特别是在最高和最低流量期间，仍然没有达成一致意见。这是因为森林采伐或其他森林干扰与河川流量之间的联系本质上是一个“黑箱”，影响河川流量的机制尚不清楚。这项研究将通过调查当代森林管理如何影响加利福尼亚沿海流域的水运动和储存，拓宽我们对森林水文学过程的理解。这项研究的结果将为推动沿海流域新的森林管理提供证据，并使人们更好地了解植被与供水之间的联系。这些结果将与美国农业部林业局和加州林业和消防部共同产生，后者将利用这些结果更新加州的森林实践规则。提高我们对森林干扰如何影响集水区储水和放水的定量认识，变得越来越重要。然而，目前还不清楚干扰是如何在除年水平衡以外的时间尺度上影响水分区的。这是因为流量增加的机制只能在成对的流域研究中推断出来，而成对的流域研究是量化森林扰动水文效应的最常用工具。结合质量平衡和双水同位素方法，有可能极大地提高我们对扰动对驱动水储存和释放的过程和机制的影响的理解。在这里，假设森林流域的生态水文响应与干扰的严重程度成正比。利用不同的森林采伐强度（去除预处理植被的0%、35%、55%和75%）作为研究森林扰动的机制，将解决以下研究问题：扰动水平的增加如何影响不同山坡位置的水收支？森林扰动如何影响土壤、地下水、溪流和树木之间的水分离？为了回答这些问题，本研究采用了一种新颖的方法，通过结合质量平衡分析和双水同位素，将森林干扰影响水收支、地下水运动和植物水分利用的过程联系起来。将监测水收支的所有组成部分（即水流、土壤水分、地下水、蒸散和雾），并与双稳定同位素（2H和18O）耦合。本研究还提出了实地水文研究的关键要求，为水文模型提供信息，以回答有关干扰对水资源影响的关键问题。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Over half of the freshwater supply in the contiguous United States originates in forested watersheds. It is thus critical that forested headwater catchments are properly managed to ensure clean and ample water supplies for aquatic ecosystems and downstream communities. Research on forested experimental watersheds has established that reducing forest cover generally increases water yield and that afforestation decreases water yield. However, there is still not agreement on the magnitude and persistence of changes in streamflow, particularly during periods of the highest and lowest streamflow. This is because the connection between forest harvesting, or other forest disturbances, and streamflow is essentially a "black box", whereby the mechanisms influencing streamflow are not understood. This research will broaden our process-based understanding of forest hydrology by investigating how contemporary forest management affects water movement and storage in a well-studied coastal California watershed. Results of this research will provide evidence to motivate new forest management in coastal watersheds and lead to better foundational knowledge of the linkages between vegetation and water supply. These results will be generated in conjunction with the USDA Forest Service and the California Department of Forestry and Fire Protection, which will use the results to update California's Forest Practice Rules. It is increasingly critical to improve our quantitative understanding of how forest disturbances affect the storage and release of water through catchments. However, it is not yet understood how disturbances impact water compartmentalization at time scales other than the annual water balance. This is because the mechanisms by which streamflow increases can only be inferred in paired watershed studies, which have been the most popular tool for quantifying hydrological effects of forest disturbance. A combined mass balance and dual water isotope approach offers the potential to critically improve our understanding of the effects of disturbances on the processes and mechanisms that drive water storage and release. Here, it is hypothesized that the ecohydrological response of a forested watershed is proportional to the severity of disturbance. Using different intensities of forest harvesting (0%, 35%, 55%, and 75% removal of pre-treatment vegetation) as a mechanism for studying forest disturbances, the following research questions will be addressed: How do increasing levels of disturbance affect the water budget at different hillslope positions? How does forest disturbance affect the separation of water between soils, groundwater, streams, and trees? To answer these questions, this study takes a novel approach to connect the processes by which forest disturbance affects water budgets, subsurface water movement, and plant water use by combining a mass balance analysis and dual water isotopes. All components of the water budget (i.e., streamflow, soil moisture, groundwater, evapotranspiration, and fog) will be monitored and coupled with dual stable isotopes (2H and 18O). This study also addresses critical calls for field-based hydrologic research to inform hydrologic models to answer key questions about disturbance impacts on water resources.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.