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

水陆过渡带是了解景观生物地球化学的关键环境。在温带流域，这些地区一般以河岸带为主，由于这些地区微生物活动增加，而且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流方面具有重要意义，因此被确定为生物地球化学特别感兴趣的地区。在南极干旱河谷，由于水在这一极地沙漠中的巨大重要性，以及干旱山谷生态系统的物质和能量收支与水文学联系在一起，陆地-水生过渡地带是有趣的景观特征。将在南极洲干旱河谷研究水陆过渡带的水文边缘，以回答两个关键问题：(1)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)这些过渡带的营养循环趋势(例如氮循环)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的差异(例如氧化还原电位)？确定这些界面的水文梯度为评估自然条件、微生物生物多样性和功能对生物地球化学循环的相对影响提供了机会。将在水文边缘范围内进行协调的水文、生物地质化学和分子微生物研究，研究目标如下：确定沉积物特性、多年冻土和活跃层动力学以及地形对水文边缘地下水分含量和分布的作用，确定物理条件(即水分、氧化还原电位和pH)或特定微生物群落(例如反硝化细菌)对水文边缘中氮的转化的影响程度，并描述饱和地带的微生物群落结构和功能。这项拟议的研究将提供一个更好的了解液态水、土壤、微生物群落和生物地球化学在干旱山谷重要的水文边缘景观单元内的相互作用。干旱山谷、溪流和湖泊是独一无二的，因为较高的植被对水的运动没有影响，因此可以为了解物理和水文对微生物生态和生物地球化学的影响提供一个模式系统。因此，这些发现将有助于南极科学以及对全世界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。将通过一个项目网站传播信息，外联活动将包括在所涉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.