Impact of Changing Flood Frequency on Sediment Connectivity Between River Channels and their Riparian Margins

在健康的溪流中，溪流和其泛滥平原之间存在广泛和持续的营养物质和沉积物交换。因此，重新建立这种交流往往是河流恢复的主要重点。即使在健康的河流中，极端降水事件的频率和幅度的预期变化，加上土地利用的变化，可能会改变河流和泛滥平原之间的营养物质和沉积物的交换，可能会通过改变河道与其边缘之间的营养物质交换平衡来改变河岸生态。如果泛滥平原的沉积物受到污染，河流-泛滥平原交换的改变可能导致以前隔离在泛滥平原上的污染物输出到下游河口和终端湖泊。该项目的目的是更好地了解河流及其泛滥平原之间泥沙交换的水文控制，以便我们能够预测和准备应对气候变化对河岸生态系统可能产生的影响。此外，我们还将建立一个外展项目，作为NSF赞助的将研究生与K-12科学课堂联系起来的项目的一部分。在这个项目的支持下，研究生将与当地一位来自资源匮乏的农村地区的中学教师合作，开发一个基于探究的项目，旨在提高学生对水文和水资源的理解和兴趣。使用最近开发的一种方法，结合放射性核素7Be和210Pb和水中氢的稳定同位素(2H)的测量来量化个别风暴事件中细颗粒沉积物的连通性，研究人员建议重复评估细粒沉积物来源以及控制美国康涅狄格河砾石河床支流中净河床到边缘沉积物通量的大小和方向的因素。假设有足够的流量来调动悬浮泥沙，研究人员假设存在一个临界流量，在该临界流量下，悬浮泥沙的净迁移是从河床到边缘，超过这个临界流量，净迁移是从边缘到河床或出流域。研究人员试图确定这一临界流量的季节性，以及悬浮泥沙净转移对偏离临界流量的敏感性。他们预计，目前在自然系统中，当流量低于临界值时，河滩上的净沉降量将被大流量事件期间河滩的净侵蚀所平衡。因此，极端降水事件频率的增加可能导致来自泛滥平原的沉积物、营养物质和颗粒结合污染物的整体净侵蚀。

In healthy streams there is an extensive and on-going exchange of nutrients and sediment between the stream and its floodplain. As a result, re-establishing this exchange is often a primary focus of river restoration. Even in healthy streams, expected changes in the frequency and magnitude of extreme precipitation events, coupled with changes in land use, may alter the exchange of nutrients and sediment between the stream and the floodplain, possibly altering riparian ecology by changing the balance of nutrient exchanges between a channel and its margins. If the floodplain sediments are contaminated, alterations of stream-floodplain exchanges may results in the export of contaminants previously sequestered on floodplains to downstream estuaries and terminal lakes. The objective of this project is to better understand the hydrologic controls on the exchange of sediment between streams and their floodplains so that we can predict and prepare for possible impacts of climate change on riparian ecosystems. In addition, we will build on an outreach project developed as part of an NSF-sponsored linking graduate students with K-12 science classrooms. The graduate student supported by this project will work with a local middle school teacher from an under-resource rural district to develop an inquiry-based project designed to increase students' understanding of, and interest in, hydrology and water resources.Using a recently-developed methodology that combines measurements of the fallout radionuclides 7Be and 210Pb and the stable isotopes of hydrogen (2H) in water to quantify fine sediment connectivity during individual storm events, the investigators propose to repeatedly assess fine-grained sediment sources and the factors controlling the magnitude and direction of net channel bed-to-margin sediment flux in a gravel-bedded tributary of the Connecticut River (USA). Given sufficient discharge to mobilize suspended sediment, the investigators hypothesize that there exists a critical discharge, below which the net transfer of suspended sediment is from the bed to the margins, and above which, the net transfer is from the margins to the bed or out of the watershed. The investigators seek to determine the seasonality of this critical discharge and the sensitivity of the net transfer of suspended sediment to departure from the critical discharge. They expect that currently in natural systems net deposition onto the floodplain during discharges less than the critical value is balanced by net erosion from the floodplain during high discharge events. Thus, an increase in the frequency of extreme precipitation events could result in an overall net erosion of sediment, nutrients, and particle-bound contaminants from the floodplain.