Prediction of hyporheic exchange and solute transport dynamics in a headwater tributary of the Illinois and Mississippi River systems

伊利诺伊州和密西西比河系统源头支流的潜流交换和溶质输运动态的预测

• 批准号: 0408744
• 负责人: Aaron Packman
• 金额: $ 36万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-01 至 2008-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0408744&HistoricalAwards=false
• 关键词: Prediction; hyporheic; exchange; solute; transport

0408744PackmanProject Summary: Water and solute exchange between streams and the surrounding subsurface(hyporheic exchange) has recently been recognized as a critical process in the cycling of many importantsubstances in watersheds. Hyporheic exchange has particularly been shown to influence nutrient andcarbon dynamics, and the fate and transport of contaminants in surface waters. These issues have risen tothe forefront in the Midwestern U.S. because substantial nitrate loads from agriculture and urban centerscontribute to chronic hypoxia in the Gulf of Mexico. Despite the clear link that exists between hydrologicprocesses in headwater streams, denitrification efficiency in removing stream nitrate, and nitrogen loadsreaching the Gulf, our current understanding of these processes in low-gradient, sand-bed streams islargely empirical. Most glaring is the lack of, fundamentally-based, predictive models for hyporheicexchange in sand-bed streams, which has prevented the transfer of experimental observations gained atone site to other sites, or even to the same site under different flow conditions.Our objective is to collect a definitive data set from a low-gradient, sand-bed stream and test theapplicability of several fundamental, process based models of hyporheic exchange that have provensuccessful in laboratory flumes. We seek to both advance our fundamental understanding of hyporheicexchange processes in real stream, but also to assess the improvements in prediction of solute transportthat are possible for a variety of flow and geomorphic conditions. The stream selected for intensive studyis Sugar Creek, a headwater stream in the agricultural region along the northern Illinois-Indiana border.Sugar Creek is representative of many low-gradient streams in agricultural headwater areas that aretributary to the Illinois and Mississippi River systems. We propose to conduct detailed tracer experimentsand related physical measurements that will be notable because they will resolve hyporheic flow paths,solute transport, and controlling processes with an unprecedented level of detail. In-stream soluteinjections will be undertaken in several seasons in a 3 to 4 kilometer long reach of Sugar Creek. Stream-tracerdata will be used to assess bulk transport integrated over 8 to 10 sub-reaches (50 300 m long)representing variable geomorphic conditions. Several of those sub-reaches will be thoroughlycharacterized in terms of their streambed topography and morphology, cross-channel flow variability,sediment characteristics, and subsurface movement of the solute tracer. This unprecedented level ofdetail will be made possible using state of the art measurement technologies. The resulting data sets willsupport the application of a suite of fundamental, predictive, process-based models of hyporheic exchangeand its effects on downstream solute transport. The models will be evaluated in terms of their ability topredict not only reach-averaged tracer concentration data, but also point estimates of interfacial hyporheicflux and porewater tracer concentrations. Based on fundamental theory, we will develop and testapproaches for upscaling rates of hyporheic exchange to predict solute transport in the entire study reachunder seasonally varying conditions. In sum, we will apply several modeling approaches of differingsophistication in order to 1) evaluate our current ability to predict hyporheic exchange in sand bed streamsfrom first principles, and 2) develop reasonable approaches for upscaling the computations so that solutetransport can be predicted with a specified level of uncertainty for longer stream reaches.Because this study is focused on fundamental processes that occur widely, this work will have verybroad scientific impacts and will be used to address multiple pressing societal concerns. Detailedunderstanding of the relationship between stream/sedimentary conditions and hyporheic exchange willfacilitate improved understanding of nutrient dynamics, carbon cycling, and releases from contaminatedsediments. Our goals for predictions (in terms of uncertainty and spatial resolution) are compatible withfuture applications in reach and basin-scale water-quality models. In particular, the choice of Sugar Creekas the intensive study site will provide critical hydrologic information to support complementary studieson nitrate fluxes and sedimentary denitrification in the headwaters of the Mississippi River basin. Theproject's broader impacts will also be increased by the synergistic activities of the PI's. Both PI's have astrong history of involvement in scientific organizations, and the project's themes will be reflected inactivities such as special sessions at major technical meetings. We will particularly seek to broaden thegeneral contribution of this work by encouraging interdisciplinary and international communication andinter-site comparisons. The project will also contribute considerably to human resource development,both through direct training of students and via the use of the field site for educational demonstrations.

0408744 Packman项目摘要：溪流和周围地下水之间的水和溶质交换（潜流交换）最近被认为是流域中许多重要物质循环的关键过程。特别是，潜流交换已被证明会影响营养物和碳的动态，以及污染物在地表沃茨中的命运和迁移。这些问题已经上升到美国中西部的最前沿，因为来自农业和城市中心的大量硝酸盐负荷导致了墨西哥湾的慢性缺氧。尽管在水源流中的水文过程、去除流中硝酸盐的反硝化效率和到达海湾的氮负荷之间存在明确的联系，但我们目前对低梯度砂床流中这些过程的理解主要是经验性的。最突出的是缺乏，基本上为基础的，预测模型的hyporheicexchange在砂床河流，这阻碍了转移的实验观测获得在一个网站到其他网站，甚至同一网站在不同的流动条件下。我们的目标是收集一个明确的数据集，从一个低梯度，砂床河流和测试的适用性的几个基本，在实验室水槽中证明是成功的基于过程的潜流交换模型。我们寻求既推进我们的hyporheicexchange过程在真实的流的基本理解，但也要评估溶质transportthat是可能的各种流量和地貌条件的预测的改进。选择进行深入研究的河流是糖溪，它是北方伊利诺斯州-印第安纳州边界沿着农业区的一条源头河流。糖溪是伊利诺斯州和密西西比河流域支流农业源头地区许多低坡度河流的代表。我们建议进行详细的示踪剂实验和相关的物理测量，这将是值得注意的，因为他们将解决hyporheic流动路径，溶质运移，并控制过程与前所未有的详细程度。在流溶质注入将在几个季节在3至4公里长的糖溪河段进行。溪流追踪数据将用于评估代表不同地貌条件的8至10个子河段（50至300 m长）的整体运输。这些子河段中的几个将在其河床地形和形态，跨通道流量的变化，沉积物的特性，和地下运动的溶质示踪剂彻底characterizedly。这种前所未有的细节水平将有可能使用最先进的测量技术。由此产生的数据集将支持一套基本的，预测的，基于过程的模型hyporheic exchange及其对下游溶质运移的影响的应用。这些模型将根据其预测能力进行评估，不仅达到平均示踪剂浓度数据，而且界面hyporheicflux和孔隙水示踪剂浓度的点估计。基于基本理论，我们将开发和测试方法的放大率hyporheic交换预测溶质运移在整个研究reachunder季节性变化的条件。总而言之，我们将应用几种不同复杂程度的建模方法，以便1）评估我们目前根据第一原理预测砂床流中的渗流交换的能力，以及2）开发合理的方法来扩大计算范围，以便可以在指定水平的不确定性下预测溶质迁移更长的河流河段。由于这项研究的重点是广泛发生的基本过程，这项工作将产生非常广泛的科学影响，并将用于解决多个紧迫的社会问题。详细了解河流/沉积条件和潜流交换之间的关系将有助于更好地了解营养动态，碳循环和污染沉积物的释放。我们的预测目标（在不确定性和空间分辨率方面）与未来在河段和流域尺度水质模型中的应用是兼容的。特别是，选择糖溪作为密集的研究地点将提供关键的水文信息，以支持补充studieson硝酸盐通量和沉积反硝化作用在源头的密西西比河流域。该项目的更广泛的影响也将通过PI的协同活动来增加。这两个PI都有参与科学组织的强烈历史，项目的主题将反映在诸如主要技术会议的特别会议等活动中。我们将特别寻求通过鼓励跨学科和国际交流以及站点间比较来扩大这项工作的总体贡献。该项目还将通过直接培训学生和利用实地进行教育示范，大大促进人力资源开发。