The Role of Protozoa in the Carbon Cycle of a Subterranean Estuary

伊丽莎白·B·库贾温斯基-伍兹霍尔海洋研究所含水层系统中的碳循环，特别是原核生物和真核生物微生物的作用，人们知之甚少。海洋和淡水系统的大量工作表明，真核生物，如原生动物，在所有水生环境--从营养丰富的沿海系统到营养贫乏的大洋中部环流--的碳循环和营养循环中发挥着基本作用。尽管如此，原生动物在含水层系统中的作用已经通过相对较少的研究得到了检验。考虑到这些生物在其他水生环境中发挥的关键作用，有理由认为它们在地下碳循环和营养循环中发挥着基础性作用。现在是时候调查存在哪些原生动物物种，它们捕食哪些细菌，以及原生动物放牧对地下水中碳循环和营养循环的影响。这项工作的目的是利用稳定的同位素，结合地球化学和微生物方法，研究原生动物对科德角地下河口营养物质再生速率和碳再矿化的影响。这项工作将使用13C标记的底物，如醋酸盐，来追踪活跃的细菌和原生动物群落。沉积物将从地下河口的淡水和咸水末端收集，并将用于建立流通柱。这些柱子将与从河口适当地点抽出的地下水一起培养，以保持原地盐度和离子组成。地下水将用13C底物进行修正。同位素标记从底物到有机物的移动将通过无机碳(含水的二氧化碳物种)、整体有机碳(TOC/DOC)和小有机分子(挥发性有机酸和氨基酸)的同位素比质谱学来监测。将通过检查同位素标记的核酸和磷脂脂肪酸(PLFA)来评估将该标签纳入微生物生物量的情况。活跃的细菌和原生动物物种将通过其同位素标记的rDNA或rRNA序列来识别。原生动物和细菌的相对作用将通过1.0微米过滤和非过滤地下水的并行柱培养来评估。据我们所知，这项拟议的工作是第一项将原生动物群落组成与淡水和咸水含水层中的营养再生和碳再矿化直接联系起来的研究。这一组微生物的研究程度很低，这项研究的结果有可能阐明含水层沉积物中微生物活动的现有范例之外的循环过程。此外，这里开发的方法一般可应用于从淡水系统到海洋沉积物等多种环境中的生态和生物地球化学研究。

EAR-0525166Elizabeth B. Kujawinski - Woods Hole Oceanographic InstitutionThe carbon cycle in aquifer systems, and particularly the role of prokaryotic and eukaryotic microbes, is poorly understood. A large body of work in marine and freshwater systems has indicated that eukaryotes such as protozoa play fundamental roles in the carbon and nutrient cycles in all aquatic environments - ranging from nutrient-rich coastal systems to nutrient-poor mid-ocean gyres. Nevertheless, the role of protozoa in aquifer systems has been examined by a relatively small number of studies. Given the pivotal role these organisms play in other aquatic environments, it is reasonable to assume that they play fundamental roles in the carbon and nutrient cycles of the subsurface. It is time to investigate which protozoan species are present, which bacteria they graze upon and the impact of protozoan grazing on the carbon and nutrient cycles in groundwater. The goal of this work is to utilize stable isotopes in combination with geochemical and microbial methods to study the effect of protozoa on nutrient regeneration rates and carbon remineralization in a subterranean estuary on Cape Cod MA. This work will use 13C-labeled substrates such as acetate to track the active bacterial and protozoan community. Sediment will be collected from the freshwater and saline end-members of the subterranean estuary and will be used to establish flow-through columns. These columns will be incubated with groundwater pumped from the appropriate site in the estuary to maintain the in situ salinity and ion composition. Groundwater will be amended with 13C-substrates. The movement of the isotopic label from substrate to organic matter will be monitored by isotope-ratio mass spectrometry of inorganic carbon (aqueous CO2 species), bulk organic carbon (TOC / DOC) and small organic molecules (volatile organic acids and amino acids). Incorporation of the label into microbial biomass will be assessed by examination of isotopically-labeled nucleic acids and phospholipid fatty acids (PLFAs). Active bacterial and protozoan species will be identified by their isotopically-labeled rDNA or rRNA sequence. The relative roles of protozoa and bacteria will be assessed by parallel column incubations with 1.0-um filtered and non-filtered groundwater. The proposed work is the first study, to our knowledge, that directly links protozoan community composition to nutrient regeneration and carbon remineralization in fresh and saline aquifers. This group of microbes is vastly under-studied and the results of this study have the potential to elucidate recycling processes outside the current paradigm of microbial activity in aquifer sediments. Furthermore, the methods developed here can be generally applied to ecological and biogeochemical studies in numerous environments, ranging from freshwater systems to marine sediments.