Collaborative Proposal: Landscape evolution and sediment-nutrient fluxes in a wetland-stream restoration experiment

设计具有改善生态系统服务的高潜力的可持续河流和河岸生态系统的先决条件是增加关于这些系统如何演变和应对环境变化和人类影响的多学科知识。在宾夕法尼亚州东南部的大泉运行（BSR）恢复实验的目标是更好地了解地质，生物和环境机制负责发展和稳定的景观格局在浅植被流系统，并测试一个新的范式流湿地恢复。这种新方法是基于这样一种假设，即去除掩埋了大约三个世纪的全新世湿草甸的历史沉积物，可以有效地恢复一些生态系统功能。 恢复的目标包括加强恢复区内河道和浅层地下水之间的水文交换，增加从泉水中流出的地下水在富含有机物的洪泛区的停留时间，并通过减少流出恢复河段的地表水中的沉积物和营养物负荷来改善水质。 地表水和地下水之间的水和营养物质交换促进了湿地生态系统中沉积物和营养物质的去除，其中地表水流速低，有机碳可用性高。恢复前和恢复后的数据比较，使我们能够确定是否这些和其他恢复目标的实现，并评估如何恢复后的初期湿地景观演变。 在来自12个机构和学术机构的26名科学家和资源管理人员的团队中，我们最近完成了BSR恢复前监测的第三年。 2011年8月完成1 km谷底修复后，开始修复后监测。水质监测包括美国地质勘探局三个溪流测量站（配备浊度传感器和悬浮沉积物采样器）、18个美国地质勘探局压力计和美国环保局在恢复流域内安装的30多口浅层地下水威尔斯井的连续运行。 此外，我们使用数值模拟1）调查在一系列环境条件下河流-洪泛区系统的演变和稳定性，2）确定地下水流路径和营养转化区，3）预测这种新的河流恢复模式在当今沉积物输入和水文通量下是否可持续。这项工作的结果将对恢复河流和改善水质产生广泛的影响。在这项工作之前，河流恢复的主要范例是基于这样的假设，即河流损害的原因主要是现代土地利用的结果（例如，城市化地区过多的雨水径流），而不是几个世纪以来人类影响的遗产，包括将原始湿地-溪流景观掩埋在数米或更深的历史淤泥之下。在BSR恢复涉及删除历史沉积物，以适应风暴流在整个谷底，并在一个低得多的速度，流深和剪切应力比受损状态。 我们预计，这种沉积物清除和湿地恢复将是一种可持续的手段，重建生态系统的多样性和功能，减少暴雨水排放到下游，并改善水质的流域，类似的损害已经确定。

Prerequisite to designing sustainable stream and riparian restorations with high potential for improved ecosystem services is to increase multi-disciplinary knowledge of how these systems evolve and respond to environmental change and human impacts. The goal of the Big Spring Run (BSR) restoration experiment in southeastern Pennsylvania is to better understand the geological, biological, and environmental mechanisms responsible for development and stability of landscape patterns in shallow vegetated flow systems, and to test a new paradigm of stream-wetland restoration. This new approach is based on the hypothesis that removal of historic sediment that buried a pre-existing Holocene wet meadow for approximately three centuries can effectively restore a number of ecosystem functions. Goals of the restoration include enhancing hydrologic exchange between stream channels and shallow groundwater within the restoration area, increasing the residence time of groundwater emanating from springs onto an organic-rich floodplain, and improving water quality by reducing sediment and nutrient loads in surface water flowing out of the restored reach. The exchange of water and nutrients between surface and ground water fosters removal of sediment and nutrients in wetland ecosystems where surface water flow speeds are low and organic carbon availability is high. Comparison of pre- and post-restoration data enables us to determine whether or not these and other restoration goals are achieved, and to evaluate how an incipient wetland landscape evolves after restoration. With a team of 26 scientists and resource managers from 12 agencies and academic institutions, we recently completed the 3rd yr of pre-restoration monitoring at BSR. Post-restoration monitoring began after 1 km of valley bottom restoration was completed in August, 2011. Water quality monitoring includes continuous operation of three USGS stream gaging stations (with turbidity sensors and suspended sediment samplers), 18 USGS piezometers, and over 30 shallow groundwater wells installed by USEPA within the restoration watershed. In addition, we use numerical modeling to 1) investigate the evolution and stability of stream-floodplain systems over a range of environmental conditions, 2) identify ground water flow paths and zones of nutrient transformation, and 3) predict whether this new paradigm of stream restoration will be sustainable under present-day sediment inputs and hydrologic fluxes. Results of this work will have broad implications for restoring streams and improving water quality. Prior to this work, the dominant paradigm for stream restoration was based on the assumption that causes of stream impairment are largely the result of modern land use (e.g., excess storm water runoff from urbanizing areas) rather than a legacy of centuries of human impacts that included the burial of original wetland-stream landscapes beneath several meters or more of historic mud. Restoration at BSR involved removing historic sediment so as to accommodate storm flow within the entire valley bottom, and at a much lower velocity, flow depth, and shear stress than in the impaired state. We anticipate that such sediment removal and wetland rehabilitation will be a sustainable means of reestablishing ecosystem diversity and function, reducing storm water discharge to downstream reaches, and improving water quality in watersheds where similar impairments have been identified.