This project addresses three overarching questions: 1) How do discrete hydrologic flowpaths differ in the timing, amounts and forms of C, N, and Hg transferred across terrestrial-aquatic interfaces? 2) How does variation in hydro-biogeochemical exports from terrestrial ecosystems impact community structure and trophic transfers of C, N, and Hg in aquatic food webs? 3) How is the exploitation of C, N, and Hg sources by keystone aquatic consumers influenced by their spatial distribution and movements? Researchers will approach a complex landscape of forests, streams, wetlands and lakes at the 108-year-old University of Michigan Biological Station (UMBS) using the concept of hydrologic diversity—spatiotemporal variation in the quantity and quality of water moving across terrestrial-aquatic interfaces—as an organizing framework. Recognizing that hydrologic inputs derive from different source areas, with distinct earth materials, soils, and vegetation types, and also that hydrologic source areas change over multiple timescales (events, seasons, years), researchers will quantify spatial and temporal variation in hydrology, biogeochemistry, community structure and trophic dynamics, with the goal of integrating these components equally, in the spirit of true ecosystem science. Through this approach, researchers will build upon—but more importantly integrate—decades of ecosystem and organism investigation at this field station. Researchers will monitor and sample surface, shallow and deep groundwater fluxes, use tracer studies and spatially explicit flow modeling to constrain connectivity and source areas. These hydrologic studies will integrate with biogeochemical investigations of the amounts and forms of C, N, and Hg in soils, sediments, and waters, with special focus on partitioning particulate vs. dissolved forms, using spectrometric (GC/MS), spectroscopic (FTIR), and isotopic (AMS, IRMS) methods to quantify variation in the age, source, functional and molecular composition of organic matter in samples collected over space and time. Whole-organism, tissue- and compound-specific isotopic analyses and mixing model approaches will enable studies of the trophic dynamics of C, N, and Hg within aquatic organisms, which researchers will combine with community composition, diversity, and structure analyses to link hydrologic fluxes of elements from terrestrial ecosystems to their impacts on aquatic ecosystems.