Water flux and nitrogen cycling in the hyporheic zones of a semi-arid watershed: Hydrologic and geomorphic driving forces in a transitional climate

[450317]潜流交换，即地表水在河岸沉积物中的暂时储存，影响溶质（包括营养物质）通过流域的运输。与其他流道的水相比，流入潜流带的水停留时间更长，与生物地球化学活性沉积物的相互作用更多。在半干旱的山间流域，在高山集水区和沙漠低地之间的气候过渡中，还没有研究过低潮通量率和地球化学。在湿润地区，河流曲流、可变流速和沉积物的水力传导性增强了流域的低潜流交换。在缺水地区，其他地貌特征，特别是海狸坝，可能同样影响地下交换。我们建议在一个具有显著海狸活动的山间半干旱流域完成潜流相互作用和氮吸收潜力的深入研究。该研究将包括实地实验和数值水文模型，旨在1.)确定和量化地下通道以及水和溶解溶质穿过地表水-地下水界面的通量；2.)确定地下通量变化的原因。我们将验证以下假设：与其他地貌和水文控制措施的影响相比，河流内的水流障碍物，特别是小型海狸坝，特别增强了沿半干旱河流的潜流带的范围。我们将通过对一系列流内示踪剂测试进行反向建模来验证我们的假设，以表征怀俄明州红峡谷溪不同河段的低循环存储参数。我们将使用达西通量计算和近流井示踪剂的观察来独立测试流内示踪剂测试的结果。我们将检验一个假设，即低循环相互作用程度越高，硝酸盐的吸收潜力越大。在流内示踪剂测试中，溶解的硝酸盐将与保守示踪剂配对。利用下游硝酸盐浓度的下降速率、氨和其他氮物种的测量以及指数营养吸收模型，我们将量化红峡谷溪的氮吸收长度，并将这些结果与潜流交换的水文测量结果进行比较。此外，我们将进行微生物调查，结合分子技术和近溪流水的地球化学分析，以独立评估反硝化和氮吸收在多大程度上推动了潜流带的氮处理。流内示踪剂测试的结果本质上是经验性的，因此很难推广到其他地点。因此，我们将使用近流路径的三维数值计算机模型来评估控制通过潜流带的空中范围和通量的物理过程。这些模型的结果将与河流地貌和沉积学特征的详细测量相结合，在一系列多变量地统计学方法中探索哪些河流特征对研究环境和其他类似顺序的河流的潜流交换影响最大。该项目将建立在雪城大学、密苏里大学布兰森地质野外营地和怀俄明州自然保护协会之间正在进行的合作关系的基础上。这些机构之前的合作导致了红峡谷河流域部分地区的水文仪器，用于从冰川历史到生态学等领域的学生研究和教育。我们将在先前工作的基础上，用仪器设备加强该站点，以提供流域尺度的研究级水文数据。通过这个项目，来自全国各地在布兰森地质野外营地学习的学生将有前所未有的机会在红峡谷溪流域的更广泛的地点进行更广泛的水文地质野外实验。此外，中央怀俄明学院（Central Wyoming College）是一所两年制社区学院，招收了大量美国原住民学生，该校的学生将被招募来直接参与该项目，担任暑期研究助理。这些合作，从本科生到研究生，将有可能在本地和更大范围内产生广泛的教育影响。

0450317SiegelHyporheic exchange, the temporary storage of surface water in stream bank sediments, affects the transport of solutes, including nutrients, through watersheds. Water diverted into the hyporheic zone has a longer residence time and more interaction with biogeochemically active sediments than water in other flow paths. Hyporheic flux rates and geochemistry have not been studied in semi-arid intermountain watersheds, transitional in climate between alpine catchments and desert lowlands. Hyporheic exchange in watersheds in humid regions is enhanced by stream meanders, variable flow rates, and sediment hydraulic conductivity. In water poor regions other geomorphic characteristics, particularly beaver dams, may equally influence hyporheic exchange. We propose to complete an intensive study of hyporheic interaction and nitrogen uptake potential in an intermountain semi-arid watershed with significant beaver activity. The study will include field experiments and numerical hydrologic models designed to 1.) identify and quantify hyporheic pathways and fluxes of water and dissolved solutes across the surface-groundwater interface and 2.) identify the causes of hyporheic flux variability. We will test the hypothesis that in-stream flow obstructions, particularly small beaver dams, particularly enhance the extent of the hyporheic zone along semi-arid streams compared to the effects of other geomorphic and hydrologic controls. We will test our hypothesis by inversely modeling a series of in-stream tracer tests to characterize hyporheic storage parameters along various reaches of Red Canyon Creek, Wyoming. We will use Darcy flux calculations and observations of tracers at near-stream wells to independently test the results of the in-stream tracer tests. We will test the hypothesis that reaches with a greater degree of hyporheic interaction have a greater potential for uptake of nitrate. Dissolved nitrate will be paired with the conservative tracers during in-stream tracer tests. Using the rate of decline of nitrate concentrations downstream, measurements of ammonia and other nitrogen species, and an exponential nutrient uptake model, we will quantify nitrogen uptake lengths along Red Canyon Creek and compare these results with hydrologic measures of hyporheic exchange. Furthermore, we will do microbial investigations incorporating molecular techniques and analysis of the geochemistry of near-stream waters to independently evaluate the degree to which denitrification and nitrogen uptake drives nitrogen processing in the hyporheic zone. Results of in-stream tracer tests are empirical in nature, and therefore difficult to generalize to other sites. For this reason, we will use three-dimensional numerical computer models of near-stream flow paths to evaluate the physical processes controlling the aerial extent and flux of water through hyporheic zones. The results of these models will be combined with detailed measurements of stream geomorphological and sedimentological characteristics in a series of multivariate geostatistical approaches to explore what stream characteristics most affect hyporheic exchange in the study setting and in similar order streams elsewhere. This project will build on the ongoing collaborative relationships between Syracuse University, the University of Missouri's Branson geology field camp, and the Wyoming Nature Conservancy. Previous collaborations between these institutions have resulted in hydrologic instrumentation of part of the Red Canyon Creek watershed for student research and education in fields from glacial history to ecology. We will build on this previous work, enhancing the site with instrumentation that will provide research grade hydrologic data at a watershed scale. Through this project, students from across the Nation studying at the Branson geology field camp will have unprecedented access to a broader range of hydrogeological field experiments at a wider variety of sites within the Red Canyon Creek watershed. In addition, students from Central Wyoming College, a 2-year community college with a large Native American enrollment, will be recruited to participate directly as summer research assistants for the project. These collaborations, undergraduate through graduate in level, will potentially have broad educational impact at both the local and larger scale.