Investigating the dynamic relationships between contaminant degradation and nutrient cycles to characterize the fate, transport, and impacts of multiple interacting stressors from industrial, agricultural, and oil/gas-related pollutants in the environment.
We investigate the historical deposition, distribution, and dynamic relationship between carbon, nitrogen, sulfur, and phosphorus nutrient cycling in lakes and watersheds.
The Great Lakes have had a history of water quality problems that peaked in the 1970’s with eutrophic conditions in Lake Erie. Carbon, nitrogen, and phosphorus inputs from human, agricultural, and industrial activities were recognized as contributing elements to eutrophication. Changes in environmental policies to reduce phosphorus inputs led to a decline in eutrophication from the 1970’s to the 1990’s; however, evidence for the re-eutrophication of Lake Erie from the mid-1990’s to 2015 has been reported. The environmental factors causing the re-eutrophication of Lake Erie are not well understood. Abiotic and biological mechanisms that degrade contaminants and nutrients cannot be distinguished from dispersion and dilution mechanisms based on concentration measurements. However, isotope values provide concentration-independent indicators that correspond directly to the chemical changes (bond-breaking and bond-making) occurring from the abiotic and/or biological catalysis involved in these environmental processes.
We investigate the relationship between C/N/S/P cycling in large-lake systems using compositional and isotopic indicators for key metabolites measured along depth profiles from water, sediment, and core samples. The historical deposition and the ongoing dynamics of chemical and microbial nutrient cycles are characterized to identify the environmental conditions that affect nutrient fluxes between the water, the sediment-water interface, and the sediments. The dynamics of nutrient cycling in lake sediments are used to assess the impacts of nutrient cycling on primary production and lake eutrophication.
We develop new approaches to characterize source zones for stray gases in soils and surface casing vents from the oil and gas sector.
Gas migration from subsurface gas-rich zones to the surface is a well-known issue in the oil/gas industry; however, the impacts of these methane inputs into the atmosphere have recently been identified as a more serious concern. Characterizing the source zone(s) for stray gases from leaking production, injection, and observation wells is an ongoing challenge in the oil/gas industry. Geochemical approaches based on gas compositions and stable isotope ratios are often unsuccessful in gas migration investigations. Unconventional extraction techniques complicate identifying the origin of stray gases in enhanced oil recovery and thermal operations. Uncharacterized shallow source zones and/or negligible differences in isotope ratios for hydrocarbons from production gases, injection gases, and overlying gas-rich zones restrict gas source identification. However, many of these challenges can be overcome with more comprehensive geochemical approaches using multiple compositional and isotopic tracers to characterize the distinct geochemistry of mixed and degraded gas sources migrating to the surface.
We develop approaches that integrate compound-specific isotope analysis (CSIA) with the fundamental theories of kinetic isotope effects (KIEs) to investigate the chemical and biological processes that occur to migrating gases, fluids, and contaminants as they are transported from depth to the surface and the atmosphere. We integrate multiple isotope approaches to characterize secondary isotope fractionating processes that change the chemical and isotopic tracers used to track sources and transport pathways. The dynamics of hydrocarbon cycling in soils and groundwater are used to assess the collective impacts of multiple sources and the factors that confound source identification.