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

在健康的溪流中，营养物和沉积物在溪流和漫滩之间进行着广泛和持续的交换。 因此，重建这种交换往往是河流恢复的主要重点。 即使在健康的溪流中，极端降水事件的频率和幅度的预期变化，再加上土地利用的变化，可能会改变溪流和洪泛区之间的营养物质和沉积物的交换，可能会通过改变渠道及其边缘之间的营养物质交换平衡来改变河岸生态。 如果洪泛区沉积物受到污染，河流洪泛区交换的改变可能会导致污染物的出口，以前隔离在洪泛区下游河口和终端湖泊。 该项目的目标是更好地了解河流及其洪泛区之间沉积物交换的水文控制，以便我们能够预测气候变化对河岸生态系统可能产生的影响并为此做好准备。 此外，我们将建立一个外展项目，作为NSF赞助的研究生与K-12科学教室联系的一部分。 该项目支持的研究生将与一位来自资源不足的农村地区的当地中学教师合作，开发一个以探究为基础的项目，旨在提高学生对以下方面的理解和兴趣：水文学和水资源：使用最近开发的方法，将沉降物放射性核素7 Be和210 Pb以及氢的稳定同位素（2 H）的测量结合起来为了量化个别风暴事件期间的细沉积物连通性，研究人员建议反复评估细颗粒沉积物来源和控制康涅狄格河（美国）砾石层支流中净河床至边缘沉积物通量的大小和方向的因素。考虑到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，低于该流量，悬浮泥沙的净转移是从河床到边缘，高于该流量，净转移是从边缘到河床或出流域。调查人员试图确定这一临界流量的季节性和悬浮泥沙净转移偏离临界流量的敏感性。他们预计，目前在自然系统中，在低于临界值的排放过程中，洪泛区的净沉积被高排放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河漫滩沉积物、营养物和颗粒结合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.