A Metabolically Active Transient Storage Model for Predicting Nutrient Retention in Streams

Roy Haggerty，Alba Argerich，David D.Myrold，Eugènia Martí&Amp；Nancy B.Grimm在过去的25年里，瞬时存储已经成为水文学中最重要的概念之一，有助于预测河流中的溶质和热量传输，也是河流生态学中最频繁的量化过程之一。然而，最近的研究表明，瞬时储存对溪流中营养物质的保留具有最小的解释能力。这是一个悖论，因为营养保持与有氧代谢密切相关，而有氧代谢又与瞬时储存的主要组成部分--低渗透交换密切相关。此外，其他保留养分的过程(磷的吸附和厌氧微生物过程)也应该优先发生在瞬时储存区。因此，令人惊讶的是，瞬时储存并没有更好地预测营养物质的保留。我们假设养分保留主要与代谢活跃的瞬时储存有关。新陈代谢活跃的瞬时存储(MATS)被定义为流速远低于存在显著初级生产或呼吸的平均值的水。我们预测，垫子将包括大部分潜水带和一些水池的海底区域。由于已知养分转化和新陈代谢之间的机制关系，我们预测MATS区也将是养分保留的热点。我们已经做了初步工作来开发对MAMS敏感的示踪剂Resazurin。在有氧呼吸存在的情况下，瑞珠灵迅速还原为间苯二酚。我们的测试表明，使用溪流中的天青素来测量MAT是可行的，并且可以采用一种标准化的方法来测量MATS，这类似于通常使用保守示踪剂(如氯化钠)来测量瞬时贮存量的方法。我们将进行一系列柱状和中观实验，以联系营养物质的保留和代谢(重点是呼吸)。我们还将测试不同底物和多个沉积物样本中雷公英还原和呼吸作用的关系，并进一步表征雷公英的吸附、光降解和降解。然后我们将进行实地实验，在溪流中添加营养物质和重天青。这些实验将主要在俄勒冈州的异养低营养河流中进行，但也将在亚利桑那州和西班牙进行一些实验，以增加新陈代谢的梯度和溶解无机氮与磷的比例(DIN：P)。还将在一年中的不同时间进行注射，包括俄勒冈州河流中的新陈代谢梯度，这样我们的解释就不局限于河流间的变化。河流将被调查和地貌特征，以帮助控制物理差异。提出了垫子的初步模型，并将在研究期间进一步开发。一个计算机代码将被更新和发布，该代码可以对存在MATS的溪流中的活性迁移进行建模和参数估计，其中交换的时间尺度可以是传统的指数分布或另一种分布。广泛影响：养分保持与MATS的关联将提高我们对养分保持的水文成分的理解，并帮助我们预测养分在溪流中的传输。Resazurin还原可能被证明是测量MATS的一个有价值的工具，并为基于示踪的呼吸量化开辟了道路。最后，我们将与一所小学合作，测量溪流并收集溪流营养数据，作为其科学课程的一部分。这些数据对科瓦利斯市很重要，因为有提议使用大量处理后的废水在溪流排出的分水岭进行灌溉，但没有测量标准。

A Metabolically Active Transient Storage Modelfor Predicting Nutrient Retention in StreamsRoy Haggerty, Alba Argerich, David D. Myrold, Eugènia Martí & Nancy B. GrimmTransient storage has become one of the most important concepts in hydrology in the past 25 years,helping to predict solute and heat transport in streams, and it is one of the most frequently quantifiedprocesses in stream ecology. However, recent research shows that transient storage has minimalexplanatory power for nutrient retention in streams. This is a paradox because nutrient retention isclosely tied to aerobic metabolism, which in turn is very strongly tied to hyporheic exchange, a majorcomponent of transient storage. Further, other processes that retain nutrients (sorption of phosphorus,and anaerobic microbial processes) also should happen preferentially in transient storage zones.Consequently, it is surprising that transient storage has not been a better predictor for nutrientretention.We hypothesize that nutrient retention is mostly associated with transient storage that ismetabolically active. Metabolically active transient storage (MATS) is defined as water with velocitymuch slower than the mean in which there is significant primary production or respiration. Wepredict that MATS will include much of the hyporheic zone and some benthic areas of pools. Givenknown mechanistic relationships between nutrient transformations and metabolism, we predict thatMATS zones will also be hotspots for nutrient retention.We have done preliminary work to develop a MATS-sensitive tracer, resazurin. Resazurin quicklyreduces to resorufin in the presence of aerobic respiration. Our tests indicate that it is feasible to useresazurin in streams to measure MATS, and that a standardized methodology to measure MATS canbe adopted similar to what is commonly done with a conservative tracer (e.g., NaCl) to measuretransient storage.We will conduct a series of column and mesocosm experiments to relate nutrient retention tometabolism (focusing on respiration). We will also test the relationship between resazurin reductionand respiration in different substrates and multiple sediment samples, and further characterizeresazurin sorption, photodegradation, and degradation. We will then conduct field experiments,adding nutrients and resazurin in streams. These will primarily be conducted in heterotrophic, lownutrientstreams of Oregon, but a few experiments will also be conducted in Arizona and Spain toadd a gradient in metabolism and dissolved inorganic nitrogen to phosphorus (DIN:P) ratio.Injections will also be carried out at different times of the year encompassing a metabolism gradientwithin the Oregon streams, so that our interpretations are not limited to inter-stream variability.Streams will be surveyed and geomorphically characterized to help control for physical differences.A preliminary model of MATS is presented, and will be further developed during the study. Acomputer code will be updated and released that can model and do parameter estimation for reactivetransport in streams in the presence of MATS, where the timescales of exchange may be theconventional exponential distribution or another distribution.Broader impact: Correlation of nutrient retention with MATS would improve our understanding ofthe hydrologic component of nutrient retention and help us to predict transport of nutrients in streams.Resazurin reduction could prove a valuable tool for measuring MATS, and open the way for a tracerbasedquantification of respiration. Lastly, we will work with an elementary school to gauge a streamand collect stream nutrient data as part of their science curriculum. The data are important to theCity of Corvallis because of a proposal to use a large quantity of treated wastewater for irrigation inthe watershed that the stream drains, and there is no gauge.