Collaborative Research: Hydrologic Controls over Biogeochemistry and Microbial Community Structure and Function across Terrestrial/Aquatic Interfaces in a Polar Desert

水陆过渡带是理解景观生物地球化学的关键环境。在温带流域，这些地区通常以河岸带为主，这些地区已被确定为生物地球化学特别感兴趣的地区，因为这些地方的微生物活动增加，并且因为这些水文边缘在促进和缓冲陆地和水生生态系统之间的水文和生物地球化学交换方面具有重要意义。在南极干谷，陆水过渡带是有趣的景观特征，因为水在这片极地沙漠中具有巨大的重要性，因为干谷生态系统的物质和能量预算与水文有关。将在南极洲干谷研究水陆过渡带的水文边缘，以回答两个主要问题：(1)跨水陆过渡带的水文和生物地球化学交换的主要控制因素是什么；(2)跨这些过渡带的养分循环趋势（如氮循环）在多大程度上反映了微生物群落或功能的差异与物理和化学环境（如氧化还原电位）的差异？定义这些界面的水文梯度为评估物理条件和微生物生物多样性及其功能对生物地球化学循环的相对影响提供了机会。协调水文、生物地球化学和分子微生物研究将在水文边缘进行，研究目标如下：确定沉积物特征、永久冻土和活动层动态以及地形对水文边缘次表层水含量和分布的作用，确定水文边缘氮的转化受到物理条件（即湿度、氧化还原电位和pH值）或特定微生物群落（例如反硝化菌）存在的影响程度，并确定饱和区微生物群落结构和功能的特征。本研究将对干谷重要水文边缘景观单元中液态水、土壤、微生物群落和生物地球化学的相互作用提供更好的理解。干谷、河流和湖泊是独特的，因为没有高级植被对水的运动的影响，因此可能为了解对微生物生态学和生物地球化学的物理和水文影响提供一个模型系统。因此，这些发现将有助于南极科学以及对全球河岸带和水文边缘的更广泛研究。研究生和本科生将参与实地考察和研究项目。资料将通过一个项目网站传播，外联活动将包括在有关三所大学附近的当地小学、初中和高中进行科学教育。

Aquatic-terrestrial transition zones are crucial environments in understanding the biogeochemistry of landscapes. In temperate watersheds, these areas are generally dominated by riparian zones, which have been identified as regions of special interest for biogeochemistry because of the increased microbial activity in these locations, and because of the importance of these hydrological margins in facilitating and buffering hydrologic and biogeochemical exchanges between terrestrial and aquatic ecosystems. In the Antarctic Dry Valleys, terrestrial-aquatic transition zones are intriguing landscape features because of the vast importance of water in this polar desert, and because the material and energy budgets of dry valley ecosystems are linked by hydrology. Hydrological margins in aquatic-terrestrial transition zones will be studied in the Dry Valleys of Antarctica to answer two overarching questions: (1) what are the major controls over hydrologic and biogeochemical exchange across aquaticterrestrial transition zones and (2) to what extent do trends in nutrient cycling (e.g. nitrogen cycling) across these transition zones reflect differences in microbial communities or function vs. differences in the physical and chemical environment (e.g., redox potential)? The hydrologic gradients that define these interfaces provide the opportunity to assess the relative influence of physical conditions and microbial biodiversity and functioning upon biogeochemical cycling. Coordinated hydrologic, biogeochemical, and molecular microbial studies will be executed within hydrologic margins with the following research objectives: to determine the role of sediment characteristics, permafrost and active layer dynamics, and topography on sub-surface water content and distribution in hydrologic margins, to determine the extent to which transformations of nitrogen in hydrological margins are influenced by physical conditions (i.e., moisture, redox potential and pH) or by the presence of specific microbial communities (e.g., denitrifiers), and to characterize the microbial community structure and function of saturated zones. This proposed research will provide an improved understanding of the interaction of liquid water, soils, microbial communities, and biogeochemistry within the important hydrologic margin landscape units of the dry valleys. Dry valleys streams and lakes are unique because there is no influence of higher vegetation on the movement of water and may therefore provide a model system for understanding physical and hydrological influences on microbial ecology and biogeochemistry. Hence the findings will contribute to Antarctic science as well as the broader study of riparian zones and hydrologic margins worldwide. Graduate students and undergraduate students will be involved with fieldwork and research projects. Information will be disseminated through a project web site, and outreach activities will include science education in local elementary, middle and high schools near the three universities involved.