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

SiegelHyporheic交换是河岸沉积物中地表水的临时储存，影响包括营养物质在内的溶质在流域中的传输。与其他流道中的水相比，进入潜流带的水具有更长的停留时间和更多的与生物地球化学活性沉积物的相互作用。在高山集水区和沙漠低地气候过渡的半干旱山间流域，潮汐通量速率和地球化学还没有被研究过。河流弯道、可变流量和泥沙水力传导性增强了湿润地区流域的地下水位交换。在缺水地区，其他地貌特征，特别是河狸坝，也可能同样影响地下水交换。我们建议在一个具有显著海狸活动的山间半干旱分水岭中完成一项关于海藻相互作用和氮素吸收潜力的深入研究。这项研究将包括现场实验和设计为1。确定和量化穿过地表-地下水界面的水和溶解溶质的潜流路径和通量。确定低渗通量变异性的原因。我们将检验这样一种假设，即与其他地貌和水文控制的影响相比，溪流中的水流障碍物，特别是小型河狸大坝，特别是增加了半干旱溪流低潮带的范围。我们将通过反向模拟一系列流中示踪测试来验证我们的假设，以表征怀俄明州红峡谷小溪不同范围的地下储藏参数。我们将使用达西通量计算和近流井示踪剂的观测来独立测试流中示踪剂测试的结果。我们将检验这一假设，即水中相互作用程度越高，摄取硝酸盐的潜力就越大。在流中示踪剂测试中，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、氨氮和其他氮素形态的测量以及指数养分吸收模型，我们将量化红峡谷小溪沿线的氮素吸收长度，并将这些结果与潮汐交换的水文测量进行比较。此外，我们将结合分子技术和近流水域的地球化学分析进行微生物调查，以独立评估反硝化和氮素吸收在多大程度上推动浅水区的氮素加工。流中示踪剂测试的结果本质上是经验的，因此很难推广到其他地点。为此，我们将使用近流路径的三维数值计算机模型来评估控制水通过潜流带的空中范围和流量的物理过程。这些模型的结果将与一系列多元地质统计学方法中对河流地貌和沉积学特征的详细测量相结合，以探索在研究环境中以及在其他地方类似顺序的河流中，哪些河流特征对地下水交换影响最大。该项目将建立在锡拉丘兹大学、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。这些机构之间以前的合作导致了红峡谷溪分水岭的部分水文仪器，用于从冰川历史到生态等领域的学生研究和教育。我们将在以前工作的基础上，通过提供分水岭尺度的研究级水文数据的仪器来加强网站。通过该项目，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小溪分水岭内的更多地点进行更广泛的水文地质野外实验。此外，来自中央怀俄明学院的学生将被直接招募参与该项目的暑期研究助理。中央怀俄明学院是一所两年制社区大学，招收了大量美国原住民学生。这些合作，从本科生到研究生，可能会在当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.