Research

FIELD WORK		EXPERIMENTS		MODELING
We perform field measurements to characterize mass fluxes and dynamics of chemical pollution at major point sources and contaminated sites. Field data is used to evaluate relationships between the behavior of aquatic contaminants and their surrounding environment (e.x., the impact dynamic soil moisture conditions or the effectiveness of treatment technologies) and to parameterize field- and regional-scale biogeochemical models.		We conduct laboratory experiments to derive contaminant partitioning coefficients and transformation rates. Controlled experiments in the laboratory allow us to isolate the impacts of chemical structure, hydrogeology, and the microbiome on contaminant fate and transport. Experimental design is informed by observations made during field work and statistical modeling results that reveal potential mechanistic drivers of water quality.		We develop models to explore the major drivers of water quality across scales from an erlenmeyer flask to the pan-Arctic. Modeling tools include both physical (e.g., box-models) and statistical (e.g., generalized additive models, random forests) approaches. Modeling allow us to extrapolate field and laboratory data to predict spatial and temporal patterns of contamination and assess the magnitude of current uncertainties and research gaps.

 

ONGOING RESEARCH

PFAS Biogeochemistry

Per- and polyfluoroalkyl substances (PFAS) are a large class of synthetic compounds known as forever chemicals because they do not degrade under natural conditions found in the environment. PFAS exposures through drinking water and diet have been associated with many negative health outcomes. As a result, the U.S. Environmental Protection Agency set nationwide drinking water limits for six PFAS. However, there are many thousands of PFAS, most of which we know very little about. Ongoing research aims to improve our understanding of prevalence, chemistry, and impacts of these understudied PFAS.

• Fluorine mass budgets: We are developing analytical and statistical tools to better quantify fluorinated compounds, including PFAS, at major point sources and contaminated sites. Current tools we are working on include high resolution mass spectrometry, combustion ion chromatography, the total oxidizable precursor assay, and Bayesian inference. 
• Fate and transport of polyfluoroalkyl substances (“precursors”): We are deriving precursor partitioning coefficients and transformation rates using field sampling and controlled experiments (e.g., non-equilibrium flow through column, batch microcosms) with an emphasis on how the number of perfluorinated carbons and non-fluorinated head-group chemistry impact these parameters.
• Organofluorine pharmaceuticals and agrochemicals: We are assessing the contribution of pharmaceuticals and agrochemicals to organofluorine concentrations at major point sources and aim to assess the impacts of chronic, low-level exposures to these compounds in the future.

Climate Impacts on Water Quality

Climate change is expected to impact chemical dynamics in aquatic environments by altering underlying hydrogeological and microbial controls and may exacerbate contamination in critical freshwater resources. Climate stress on water availability may also result in greater reliance on heavily contaminated sources for drinking water and agriculture, such as treated wastewater and produced water. Ongoing research aims to combine field measurements, experiments, and remote sensing data to better understand impacts of climate change on water quality. 

• Remote sensing: We are working on statistical and mechanistic models that predict water quality time series on regional scales by blending in-situ measurements and remote sensing data representing the major drivers of water quality. Current work is focused on the differential climate and ecosystem drivers of inorganic versus organic nitrogen in rivers and lakes.
• Arctic: We are particularly focused on studying climate impacts of water quality in the Arctic where direct human disturbances are minimal but the effects of climate change are more severe due to Arctic amplification.