Collaborative Research: In Situ Examination of Hydrogen Peroxide Sources and Sinks in a Slightly Alkaline Stream

光化学产生的过氧化氢（H2 O2）在阳光照射下的淡水中普遍存在，并可能发挥许多重要的地球化学作用。特别令人感兴趣的是，H2 O2可能是最重要的来源羟基自由基（OH）在表面沃茨通过还原H2 O2的Fe（II）。羟基自由基氧化是将难降解有机化合物（包括污染物和天然有机物）转化为CO2和微生物底物的有效机制。目前还不清楚是否在湖泊和海洋系统中确定的H2 O2的源和汇是最重要的控制H2 O2在流。H2 O2的还原作用，特别是，仍然是未开发的，但非常酸性的流。此外，初步模拟的理论达到规模流示踪剂注入实验表明，H2- 18 O2，与保守的示踪剂一起使用，可以是唯一有用的，以解决模拟流地球化学过程的主要问题之一（例如氮循环、污染物生物降解、吸附）：需要一种示踪剂，可以区分涉及地表水池中的瞬时储存的流动路径和通过潜流区（地下）的流动路径。然而，H2- 18 O2作为示踪剂的应用需要更好地了解H2- 18 O2在地表和地下沃茨中分解速率的控制。拟议工作的总体目标是进行第一次全面研究过氧化氢循环的天然流选择广泛代表农业源头流在美国中部的天然H2 O2和注入同位素标记的H2-直接放置在河流沉积物中的中型生态系统中的18 O2示踪剂将用于测试我们目前对阳光照射下的河流水中H2 O2源和汇的理解，以及其底层沉积物我们的研究结果将表明，是否羟基自由基的生产过氧化氢可能是一个主要的机制，间接光解的有机污染物和天然有机物的流。天然有机物的光分解具有重要意义，因为它产生生物可利用的碳基质以及二氧化碳，并且被认为是生态系统尺度碳循环的重要控制。我们的工作还可以为开发加速芬顿在农业水源等系统中的反应的方法奠定基础，以降低阿特拉津等污染物的浓度。最后，如果过氧化氢原来是一个很好的示踪剂，区分地表和地下存储在流，拟议的工作将有助于发展更好的模型的生态地球化学过程，如氮循环和生物降解的污染物在这些环境中。这项拟议的工作是一名新研究员（Durelle Scott）和一名中层女科学家（Bettina Voelker）的共同努力，并将支持科罗拉多矿业学院和内布拉斯加大学各一名研究生和一名本科生研究员。

Photochemically produced hydrogen peroxide (H2O2) is ubiquitous in sunlit freshwater and may play a number of important biogeochemical roles. Of particular interest is that H2O2 may be the most important source of hydroxyl radical (OH) in surface waters via reduction of H2O2 by Fe(II). Oxidation by hydroxyl radical is an effective mechanism for converting refractory organic compounds, including contaminants and natural organic matter, to CO2 and microbial substrates. It is still unclear whether the sources and sinks of H2O2 identified in lakes and marine systems are the most important controls on H2O2 in streams. The role of reduction of H2O2, in particular, remains unexplored in all but very acidic streams. In addition, preliminary modeling of a theoretical reach-scale stream tracer injection experiment suggests that H2-18O2, used in conjunction with a conservative tracer, could be uniquely useful for addressing one of the main problems of modeling biogeochemical processes in streams (e.g. nitrogen cycling, contaminant biodegradation, sorption): the need for a tracer that can distinguish flowpaths involving transient storage in surface water pools from flowpaths through the hyporheic zone (subsurface). However, H2-18O2's application as a tracer requires a better understanding of the controls on H2-18O2 decomposition rates in surface and subsurface waters. The overall goal of the proposed work is to conduct the first comprehensive study of hydrogen peroxide cycling in a natural stream chosen to be broadly representative of agricultural headwater streams in the central U.S. Measurement of the fate of natural H2O2 and an injected isotope-labeled H2-18O2 tracer in mesocosms placed directly into stream sediments will be used to test our current understanding of H2O2 sources and sinks in sunlit stream water and the underlying sediment. Our results will show whether hydroxyl radical production from hydrogen peroxide could be a dominant mechanism of indirect photolysis of organic contaminants and natural organic matter in streams. Photolysis of natural organic matter is of significance because it produces bioavailable carbon substrates as well as carbon dioxide, and is thought to be an important control on ecosystem-scale carbon cycling. Our work could also lay the groundwork for developing methods to accelerate Fenton's reaction in systems such as agricultural headwaters, for the purpose of decreasing concentrations of contaminants such as atrazine. Finally, if hydrogen peroxide turns out to be a good tracer for distinguishing between surface and subsurface storage in streams, the proposed work will contribute to the development of better models of biogeochemical processes such as nitrogen cycling and biodegradation of contaminants in these environments. The proposed work is a joint effort between a new investigator (Durelle Scott) and a mid-level female scientist (Bettina Voelker), and will support one graduate student and one undergraduate researcher each at the Colorado School of Mines and at the University of Nebraska.