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

一个预测河流中营养物质滞留的代谢活性瞬时储存模型Roy Haggerty，Alba Argerich，大卫D. Myrold，Eugènia Martí Nancy B.在过去的25年里，瞬时存储已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输运，并且它是河流生态学中最经常量化的过程之一。然而，最近的研究表明，瞬时存储有极小的解释能力，养分滞留在溪流。这是一个悖论，因为营养保留与有氧代谢密切相关，而有氧代谢又与潜流交换密切相关，这是瞬时储存的主要组成部分。此外，其他保留营养素的过程（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，瞬时储存并不是营养素保留的更好预测因素。我们假设营养素保留主要与代谢活跃的瞬时储存有关。代谢活性瞬时储存（MATS）是指水的速度远低于平均值，其中有显着的初级生产或呼吸。我们预测，MATS将包括大部分的潜流区和一些底栖区池。鉴于已知的养分转化与代谢之间的机制关系，我们预测MATS区也将成为养分保留的热点。在有氧呼吸作用下，刃天青迅速还原为试卤灵。我们的测试表明，在流中使用天青来测量MATS是可行的，并且可以采用类似于通常使用保守示踪剂所做的标准化方法来测量MATS（例如，我们将进行一系列的柱和围隔生态系统实验，将营养物保留与代谢（重点是呼吸作用）联系起来。我们还将测试刃天青还原和呼吸之间的关系，在不同的基板和多个沉积物样品，并进一步characterizeresazurin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刃天青。这些试验将主要在俄勒冈州的异养、低营养流中进行，但也将在亚利桑那州和西班牙进行一些试验，以增加代谢和溶解无机氮与磷的梯度（DIN：注入也将在一年中的不同时间进行，包括俄勒冈州溪流之间的代谢梯度，因此我们的解释不限于溪流之间的变化。溪流将被调查和地貌特征化，以帮助控制物理差异。提出了MATS的初步模型，并将在研究期间进一步发展。一个计算机代码将被更新和发布，它可以对存在MATS的流中的反应性传输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。养分截留与MATS的相关性将提高我们对养分截留的水文组成的理解，并有助于我们预测河流中养分的迁移。证明了测量MATS的有价值的工具，并为基于示踪剂的呼吸定量开辟了道路。最后，我们将与一所小学合作，测量河流并收集河流营养数据，作为他们科学课程的一部分。这些数据对科瓦利斯市很重要，因为有一项建议，要使用大量的处理后的废水用于灌溉流域的河流排水，没有衡量。

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.