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

河流的四个隔间之间存在着相当大的水和溶质交换：河道的快速流动部分、河道内储存区以及浅层和深层沉积区。这些隔间之间的水交换促进了溶解的营养物质的反应和清除。研究小组假设，溪流中的营养物质反应不仅受水文传输的控制，还受营养物质的化学计量比(C：N：P的比率)的控制。该团队将通过在三个不同的临界区天文台(CZO)站点(科罗拉多州的岩石山脉Boulder Creek；新墨西哥州的低营养环境Catalina-Jemez；以及爱荷华州的一处农业景观)进行现场数据收集和溪流溶质注入来验证他们的假设。在这三个地点，地质、水文和本底营养浓度有很大的差异(因此也有营养限制)。该项目将吸引多名研究生参与，强调多样性。该小组还将组织一次研讨会，以促进和鼓励河流恢复领域的主要参与者之间的互动和思想和知识的交流，特别是年轻的科学家和从业者、河流恢复公司和当地环境机构。河流及其潜水带之间的水和溶质交换导致对河流营养物质的净反应和清除。河流中的养分反应和去除(碳、氮和磷)不仅受到可用于吸收养分的生物量的限制，而且还受到特定反应的化学计量学限制。该项目的工作假设是：(1)河流中的营养物质保持不仅受水文传输的控制，而且还受营养物质的化学计量比(C：N：P)的控制；(2)河流的每个隔室(主河道、地表储存、浅/深层水生生物)有不同的最佳化学计量需要(即C：N：P)；以及(3)有氧代谢中的溶解氧消耗是一级控制，当一个隔室变得缺氧和生物地球化学过程发生变化时，它会引起C、N和P的化学计量需求的阈值变化。这些概念将通过在三个不同的临界区观测站(CZO)不同的水文条件下进行实地数据收集和流动溶质注入来测试，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、基于化学计量比权衡的营养示踪剂注射、用于螺旋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)和深(井)亚流路径。营养示踪剂注射的目的是专门破译在溪流的四个隔间中的每个隔间中对养分保留的化学计量控制。更广泛的影响将在研讨会上传达，该研讨会将确定学术研究和修复计划的互惠需求，以寻求更全面地处理溪流恢复项目。

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.