Title: Redox Transformations of Mn, Fe, and S Across the Land-to-Ocean Continuum: Hydro-biogeochemical Dynamics and Implications for Carbon Cycling and Contaminant Transport
When: Friday, January 9 at 14:00 EST
Where: Ford ES&T L1116 or Zoom (link to follow)
Abstract: Oxidation-reduction (redox) reactions drive a global biogeochemical network of couplings and feedbacks between the physical, chemical, and biological components of the biosphere. Redox-based transformations are inextricably linked to the hydrologic cycle, and from mobilizing terrestrial matter to streams and rivers for export to oceans or triggering the release of subsurface greenhouse gases to the atmosphere, hydrologic flow is the basis for the exchange of material across the landscape. In this defense, I will focus on the results of three studies that investigated the impact of hydrology-coupled biogeochemical cycling on organic matter (OM) remineralization, greenhouse gas emissions, or contaminant transport. These interdisciplinary studies combined a geochemical approach featuring the voltammetric detection of Mn, Fe, and S with analyses of hydrologic (e.g., discharge, water table) and meteorological (e.g., wind, precipitation) time series. First, I will discuss the influence of river discharge intensity on OM remineralization pathways in the northern Gulf of Mexico. Second, I will discuss the effects of hydropatterns and flow-driven redox regimes on CH4 emissions from a headwater riparian ecosystem in the Southeastern United States. Third, I will discuss the influence of differential hydrologic flow on uranium mobility in losing and gaining reaches of a contaminated headwater stream. Results of these studies demonstrate that the frequency and magnitude of hydrologically induced redox state changes increase with decreasing spatial scale. Whereas changes to the redox state in sediments of the northern Gulf of Mexico were primarily associated with seasonal river discharge and wind-driven remobilization, water table fluctuations in the headwater riparian system induced redox oscillations with frequencies of hours to days. At both scales, these oscillations are punctuated by hydro-meteorological events that create biogeochemical hot moments. As a final example, I will introduce a time series analysis of storm-driven hydro-biogeochemical cascades across a hillslope-to-stream continuum to emphasize the challenge of spatiotemporal heterogeneity in capturing the extent of these dynamics in the environment. These integrated studies advance our knowledge of hydrology-coupled biogeochemistry in marine and freshwater sedimentary environments and underscore the importance of observation-based research in monitoring water quality and understanding ecosystem function in response to anthropogenic stressors.