Collaborative Research: Deconstructing Nitrate Stable Isotope Ratios in Aquifers

合作研究：解构含水层中的硝酸盐稳定同位素比率

• 批准号: 1424720
• 负责人: Julie Granger
• 金额: $ 30万
• 依托单位: University of Connecticut
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-01 至 2019-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1424720&HistoricalAwards=false
• 关键词: Collaborative; Research; Deconstructing; Nitrate; Stable

Anthropogenic nutrient loading and the consequent eutrophication of aquatic systems pose a substantial environmental threat. Excessive nitrogen can have profound detrimental effects on the diversity and function of ecosystems, and on human health. The proposed study is an important venture to establish a robust rubric in nitrogen isotope systematic, to allow for accurate and more quantitative interpretations of nitrate isotope distributions in the environment, and thus a sound understanding of inherent nitrogen dynamics. The goal of the study is to investigate the isotope dynamics of nitrogen species in the West Falmouth Wastewater Plume in Falmouth, Massachusetts, in order to resolve differences in isotope discrimination observed between studies of mono-cultures of nitrifying and of denitrifying bacterial isolates and patterns ascribed to analogous transformations in aquatic environments. For one, nitrate 18O/16O values produced by nitrifiers in cultures reveal isotope effects that are largely overlooked when interpreting environmental trends. Second, the fractionation of 18O/16O relative to 15N/14N has a characteristic and consistent slope of ~1 in cultures of denitrifiers, in contrast to a slope of ~0.6 observed for nitrate attenuation by denitrification in aquifers. The investigators seek to (1) constrain the nitrate 18O/16O values produce by nitrification in relation to environmental conditions and (2) investigate the organism-level 18O/16O versus 15N/14N enrichment imparted on nitrate during denitrification in situ as compared to culture observations. They propose to test hypotheses with a set of in-lab incubations of environmental samples from the site, as well as an in situ tracer test. The project is in collaboration with the US Geological Survey and will support a graduate student. The investigation is important because the discordance of culture to field observations raises the possibility that isotope trends in the environment are misinterpreted, possibly overlooking important fluxes in the nitrogen mass balance of aquifers.

人为的营养物质负荷和随之而来的水生系统富营养化构成了严重的环境威胁。过量的氮会对生态系统的多样性和功能以及人类健康产生深远的有害影响。拟议的研究是一项重要的尝试，目的是在氮同位素系统中建立一个强有力的标准，以便能够准确和更定量地解释环境中的硝酸盐同位素分布，从而对固有的氮动态有一个良好的了解。本研究的目的是研究马萨诸塞州法尔茅斯西法尔茅斯污水羽流中氮物种的同位素动力学，以解决在单一培养的硝化和反硝化细菌以及归因于水环境中类似转化的模式之间观察到的同位素识别差异。首先，培养物中硝化菌产生的硝酸盐18O/16O值揭示了在解释环境趋势时基本上被忽视的同位素效应。反硝化细菌培养中18O/16O相对于15N/14N的分馏斜率为~1，而含水层中反硝化硝酸盐衰减的斜率为~0.6。研究人员试图(1)限制硝化作用产生的硝酸盐18O/16O值与环境条件的关系，以及(2)与培养观察相比较，研究在原位反硝化过程中生物水平对硝酸盐的18O/16O和15N/14N的富集量。他们建议通过一系列实验室内对现场环境样本的孵化以及现场示踪剂测试来检验假设。该项目是与美国地质调查局合作的，将支持一名研究生。这项调查很重要，因为培养与实地观察的不一致增加了环境中同位素趋势被误解的可能性，可能忽略了含水层氮物质平衡中的重要通量。