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.

0408744Packman项目摘要：溪流与周围地下之间的水和溶质交换（地表交换）最近被认为是流域中许多重要物质循环的关键过程。潜流交换尤其被证明会影响营养物和碳动态，以及地表水中污染物的命运和迁移。这些问题在美国中西部已经成为最重要的问题，因为来自农业和城市中心的大量硝酸盐导致了墨西哥湾的长期缺氧。尽管源头河流的水文过程、去除河流硝酸盐的反硝化效率和到达海湾的氮负荷之间存在明显的联系，但我们目前对低梯度沙床河流中这些过程的理解很大程度上是经验性的。最明显的是，缺乏基于基础的沙床流下流交换预测模型，这阻碍了将一个地点获得的实验观察结果转移到其他地点，甚至转移到不同流动条件下的同一地点。我们的目标是从低梯度沙床流中收集明确的数据集，并测试几种基本的、基于过程的潜流交换模型的适用性，这些模型已在实验室水槽中证明是成功的。我们寻求既增进对真实河流中地下交换过程的基本理解，又评估在各种流动和地貌条件下可能的溶质运输预测的改进。选择进行深入研究的河流是糖溪，它是伊利诺伊州和印第安纳州北部边境农业区的一条源头溪流。糖溪是农业源头区许多低梯度溪流的代表，这些溪流是伊利诺伊河和密西西比河系统的支流。我们建议进行详细的示踪剂实验和相关的物理测量，这些实验和相关的物理测量将是值得注意的，因为它们将以前所未有的详细程度解决潜流路径、溶质运输和控制过程。将在几个季节在 Sugar Creek 3 至 4 公里长的河段进行河流内溶质注射。河流追踪数据将用于评估代表可变地貌条件的 8 至 10 个支河段（长 50 300 m）的散装运输。其中一些子河段将在其河床地形和形态、跨河道流量变化、沉积物特征和溶质示踪剂的地下运动方面得到彻底的表征。这种前所未有的细节水平将通过使用最先进的测量技术来实现。由此产生的数据集将支持一套基本的、预测的、基于过程的潜流交换模型的应用及其对下游溶质运输的影响。这些模型不仅能够预测平均示踪剂浓度数据，而且还能预测界面潜流和孔隙水示踪剂浓度的点估计。基于基础理论，我们将开发和测试提高潜流交换速率的方法，以预测季节性变化条件下整个研究范围内的溶质运输。总之，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沙床流中潜流交换的能力，2) 开发合理的方法来扩大计算范围，以便可以用指定的值来预测溶质传输由于这项研究的重点是广泛发生的基本过程，因此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/沉积物条件与潜流交换之间的关系将有助于更好地了解养分动态、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）与河段和流域规模水质模型的未来应用兼容。特别是，选择糖溪作为集中研究地点将提供关键的水文信息，以支持密西西比河流域源头硝酸盐通量和沉积反硝化的补充研究。 PI 的协同活动也将增强该项目的更广泛影响。两位 PI 都有参与科学组织的悠久历史，项目的主题将反映在重大技术会议上的特别会议等不活动中。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。该项目还将通过对学生的直接培训和利用现场进行教育示范，为人力资源开发做出巨大贡献。