Doctor of Philosophy, The Ohio State University, 2020, Earth Sciences

Upland catchments play an outsized role in the processing and export of water, sediments, nutrients, and organic matter, thus strongly influencing downstream water quality. In Chapter 1, an overview of biogeochemical cycling within upland fluvial sediments is presented, focusing on key regional biogeochemical cycling patterns and solute export processes. Additionally, anthropogenic influences on this environment, such as historical mining activities and climate change, are briefly reviewed in this chapter. Chapter 2 explores the relationship between spatial hydrologic heterogeneity and microbial community assembly and functional potential within the hyporheic zone. The region of groundwater and river water mixing, known as the hyporheic zone, is a hotspot of microbial activity that influences solute export and cycling in rivers. Hyporheic mixing patterns can vary over small spatial scales, leading to heterogeneity in fluid chemistry and microbial community composition and function. Here, we integrate new mass-spectrometry data, metagenomic insights, and ecological models with previous analyses of microbial community composition and dissolved organic matter (DOM) quality to understand spatial relationships between hyporheic flow and microbial community assembly, metabolism, and DOM processing at high-resolution (100 locations) along a 200 m meander of East River, Colorado (USA). Ecological modeling revealed a strong linkage between community assembly patterns and underlying hydrologic and geochemical drivers, including the impact of physical heterogeneity (riverbed grain size) on microbial community structure. Geochemical profiles associated with upwelling groundwater suggest the influence of underlying geology, specifically Mancos-derived solutes, in driving community assembly. Distinct microbial community profiles and functional potential in zones of upwelling groundwater suggest that groundwater chemistry may have a greater influence on biogeochemical cycling wi (open full item for complete abstract)

Committee: Michael Wilkins (Advisor); Steven Lower (Advisor); Audrey Sawyer (Committee Member); Elizabeth Griffith (Committee Member) Subjects: Biogeochemistry; Earth; Ecology; Environmental Geology; Environmental Science; Geobiology; Geochemistry; Geology; Hydrology; Limnology; Microbiology; Mineralogy