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

在健康的河流中，在河流和河漫滩之间存在着广泛而持续的营养物质和沉积物交换。因此，重建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，也可能改变河流与洪泛区之间营养物质和沉积物的交换，可能通过改变河道与其边缘之间营养物质交换的平衡来改变河岸生态。如果洪泛区沉积物受到污染，河流与洪泛区交换的改变可能导致先前在洪泛区隔离的污染物向下游河口和终端湖泊出口。该项目的目的是更好地了解河流及其洪泛平原之间沉积物交换的水文控制，以便我们能够预测和准备气候变化对河岸生态系统可能产生的影响。此外，我们将在nsf赞助的研究生与K-12科学教室联系项目的基础上进一步发展。该项目资助的研究生将与一名来自资源不足农村地区的当地中学教师合作，开发一个基于探究的项目，旨在提高学生对水文学和水资源的理解和兴趣。研究人员利用最近开发的一种方法，将沉降放射性核素7Be和210Pb的测量与水中氢（2H）的稳定同位素结合起来，量化单个风暴事件期间细粒沉积物的连通性。研究人员建议反复评估细粒沉积物来源以及控制美国康涅狄格河砾石层状支流净河床到边缘沉积物通量的大小和方向的因素。如果有足够的流量来调动悬沙，研究人员假设存在一个临界流量，低于这个流量，悬沙的净转移是从河床到边缘，高于这个流量，净转移是从边缘到河床或流出流域。调查人员试图确定这一临界流量的季节性和悬浮物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，在低于临界值的流量期间，洪泛区的净沉积被高流量事件期间洪泛区的净侵蚀所平衡。因此，极端降水事件频率的增加可能导致洪泛区沉积物、营养物质和颗粒污染物的总体净侵蚀。

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.