Collaborative Research: How do interactions of transport and stoichiometry maximize stream nutrient retention?

在河流的四个区间，水和溶质有相当大的交换：河道的快速流动部分，河道内储存区，浅层和深层沉积物区。这些隔室之间的水交换促进溶解的营养反应和去除。研究小组假设，河流中的营养反应不仅受到水文运输的控制，还受到营养物质化学计量学（C:N:P的比例）的控制。研究小组将通过在三个不同的关键区域观测站（CZO）进行实地数据收集和溪流溶质注入来验证他们的假设（Boulder Creek，科罗拉多州的岩石山环境；Catalina-Jemez，新墨西哥州的低营养环境；以及爱荷华州的农业景观）。在这三个地点，在地质、水文和背景营养浓度（因此营养限制）方面存在很大的差异。该项目将吸引多名研究生参与，重点是多样性。该小组亦会举办工作坊，促进和鼓励溪流修复界的主要人士，特别是青年科学家和实践者、溪流修复公司和本地环保机构之间的互动和交流思想和知识。河流及其潜流带之间的水和溶质交换导致净反应和从河流中去除营养物质。营养物的反应和去除（碳、氮和磷）不仅受到可吸收营养物的生物量的限制，而且在化学计量上也受到特定反应的限制。该项目将基于以下假设：(1)河流中的营养物质保留不仅受水文运输控制，而且受营养物质化学计量学（C:N:P比）控制；(2)河流的每个隔室（主河道、地表水库、浅/深潜流）具有不同的最佳化学计量需求（即C:N:P）；(3)有氧代谢中溶解氧的消耗是一阶控制，当隔室缺氧和生物地球化学过程发生变化时，会导致C、N和P的化学计量需求发生阈值变化。这些概念将通过在三个不同水文条件的关键区域观测站（CZO）进行现场数据收集和溪流溶质注入来进行测试，以测试每个站点在一系列水文运输条件下的变化。该团队将部署一套方法，包括电阻率成像、基于化学计量学权衡的营养示踪剂注射、用于螺旋曲线表征的示踪剂添加（TASCC方法）、在溪流中应用“智能”示踪剂resazurin，以及使用浅（MINIPOINT采样器）和深（井）的潜流路径。营养示踪剂注射剂的设计是专门破译化学计量控制的营养保留在每四个隔间的溪流。更广泛的影响将在研讨会上进行交流，以确定学术研究和修复项目的相互需求，寻求更全面地处理河流修复项目。

There is considerable exchange of water and solutes among four compartments of streams: the fast moving part of the stream channel, in-channel storage zones, and shallow and deep sediments zones. Exchanges of water between these compartments promote dissolved nutrient reactions and removal. The team hypothesizes that nutrient reaction in streams is controlled by not only hydrologic transport, but also stoichiometry of nutrients (ratio of C:N:P). The team will test their hypotheses by conducting field data collection and stream solute injections at three contrasting Critical Zone Observatory (CZO) sites (Boulder Creek, a rocky mountain setting in Colorado; Catalina-Jemez, a low nutrient setting in New Mexico; and an agricultural landscape in Iowa). Across these three sites there is substantial variability in geology, hydrology, and background nutrient concentrations (and therefore nutrient limitations). The project will engage multiple graduate students with an emphasis on diversity. The team will also organize a workshop to promote and stimulate interaction and exchange of ideas and knowledge among the principal players in the stream restoration field, particularly young scientists and practitioners, stream restoration companies and local environmental agencies.The exchange of water and solutes among the river and its hyporheic zones result in a net reaction and removal on nutrients from the stream. Nutrient reaction and removal (carbon, nitrogen, and phosphorous) in streams is limited by not only the biomass available to take up nutrients, but is also stoichiometrically limited by the specific reaction. This project will work with the hypothesis that: (1) nutrient retention in streams is controlled by not only hydrologic transport, but also stoichiometry of nutrients (ratio of C:N:P); (2) each compartment of a stream (main channel, surface storage, shallow/deep hyporheic) has a different optimal stoichiometric need (i.e., C:N:P); and (3) depletion of dissolved oxygen from aerobic metabolism is a first-order control that causes a threshold change in the stoichiometric demand of C, N, and P as a compartment becomes anoxic and biogeochemical processes change. The concepts will be tested by conducting field data collection and stream solute injections at three contrasting Critical Zone Observatory (CZO) sites across variable hydrologic conditions at each site to test over a range of hydrologic transport conditions. The team will deploy a suite of methods including electrical resistivity imaging, nutrient tracer injections based on stoichiometric tradeoffs, the Tracer Additions for Spiraling Curve Characterization (TASCC method), application of the "smart" tracer resazurin in streams and use of shallow (MINIPOINT samplers) and deep (wells) hyporheic flow paths. Nutrient tracer injections are designed to specifically decipher stoichiometric controls on nutrient retention in each of the four compartments of the streams. The broader impacts will be communicated in a workshop setting that identifies reciprocal needs from academic research and restoration programs seeking to approach stream restoration projects more holistically.