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潜力的可持续河流和河岸恢复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。宾夕法尼亚州东南部的大春季奔流(BSR)恢复实验的目标是更好地了解浅水植被流系统中景观格局发展和稳定的地质、生物和环境机制，并测试溪流湿地恢复的新范式。这种新的方法是基于这样一种假设，即清除埋藏了大约三个世纪的全新世湿润草甸的历史沉积物可以有效地恢复一些生态系统功能。修复的目标包括加强修复区域内河道和浅层地下水之间的水文交换，增加从泉水向富含有机物质的泛滥平原排放的地下水的停留时间，并通过减少从修复河段流出的地表水中的泥沙和营养物质负荷来改善水质。地表水和地下水之间的水和营养物质的交换促进了湿地生态系统中沉积物和营养物质的清除，在那里，地表水的流速较低，有机碳的有效性很高。通过比较恢复前后的数据，我们能够确定这些和其他恢复目标是否实现，并评估恢复后早期湿地景观的演变。最近，我们与来自12个机构和学术机构的26名科学家和资源经理组成的团队，完成了BSR第三年的修复前监测。在2011年8月完成1公里的谷底修复后，开始了修复后的监测。水质监测包括美国环保局在修复流域内安装的3个USGS水系计量站(带有浊度传感器和悬浮泥沙采样器)、18个USGS压力计和30多口浅层地下水井的连续运行。此外，我们使用数值模拟1)研究河流-滩涂系统在一系列环境条件下的演变和稳定性，2)确定地下水流动路径和营养物质转化区，以及3)预测这种新的河流恢复模式在当今泥沙输入和水文通量下是否可持续。这项工作的结果将对恢复溪流和改善水质产生广泛影响。在这项工作之前，河流恢复的主要模式是基于这样的假设，即河流受损的原因主要是现代土地利用(例如，城市化地区过多的暴雨径流)的结果，而不是几个世纪以来人类影响的遗留问题，包括将原始湿地-河流景观掩埋在几米或更长的历史泥浆下。BSR的修复包括清除历史沉积物，以适应整个谷底的暴雨水流，并以比受损状态低得多的速度、水流深度和剪应力。我们预计，这种清除沉积物和湿地恢复将是重建生态系统多样性和功能、减少向下游地区排放暴雨水以及改善已发现类似损害的流域水质的可持续手段。

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.