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

河流的四个部分之间有相当大的水和溶质交换：河道的快速移动部分，河道内的存储区，以及浅和深沉积物区。这些隔室之间的水交换促进溶解的营养物反应和去除。 该团队假设，河流中的营养反应不仅受水文运输控制，还受营养物质的化学计量（C：N：P的比例）控制。 该团队将通过在三个对比鲜明的临界区观测站（CZO）站点（博尔德溪，科罗拉多的落基山脉环境;卡特琳娜-杰梅斯，新墨西哥州的低营养环境;和爱荷华州的农业景观）进行实地数据收集和流溶质注入来测试他们的假设。在这三个站点中，地质、水文和背景养分浓度（因此养分限制）存在很大差异。该项目将吸引多名研究生，强调多样性。此外，该小组亦会举办工作坊，以促进和鼓励溪流修复领域的主要参与者，特别是年青科学家和从业者、溪流修复公司和当地环保机构，互相交流意见和知识。 流中的营养物反应和去除（碳、氮和磷）不仅受到可用于吸收营养物的生物质的限制，而且还受到特定反应的化学计量限制。该项目将采用以下假设：（1）河流中的营养物保留不仅受水文输运控制，而且受营养物化学计量（C：N：P的比例）控制;（2）河流的每个分区（主河道，表面储存，浅/深潜流）具有不同的最佳化学计量需求（即，C：N：P）;（3）好氧代谢引起的溶解氧的消耗是一级控制，当隔室变为缺氧和生物地球化学过程改变时，其引起C、N和P的化学计量需求的阈值改变。这些概念将通过在三个不同的临界区观测站（CZO）进行现场数据收集和流溶质注入来测试，每个站点的水文条件不同，以测试一系列水文运输条件。该团队将部署一套方法，包括电阻率成像，基于化学计量权衡的营养示踪剂注入，螺旋曲线表征的示踪剂添加（TASCC方法），在溪流中应用“智能”示踪剂刃天青，以及使用浅（MINIPOINT采样器）和深（威尔斯）的潜流路径。营养示踪剂注入的目的是专门破译化学计量控制营养保留在每一个四个隔间的流。 更广泛的影响将在一个研讨会上进行交流，该研讨会将确定学术研究和恢复计划的相互需求，以更全面地处理河流恢复项目。

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.