RESEARCH
Photo Credit: Greg Fiske
My research expertise unites a breadth of interdisciplinary scientific and technological approaches, including the synthesis of large historical datasets, field and lab experimental studies, analytical chemistry, satellite remote sensing, geospatial analysis, as well as quantitative and predictive modeling.
Using Earth's Remotely Sensed Environment to Explain and Predict Arsenic Contamination in Groundwater
Over one billion people worldwide lack access to safe drinking water—a number that may double in the coming decades as clean freshwater becomes increasingly scarce in light of climate change. At least 200 million people in more than 70 countries drink groundwater contaminated with naturally occurring arsenic (As). Excessive exposure to this pervasive contaminant is associated with a number of severe chronic illnesses, including skin disorders, heart disease, cancers, diabetes, and cognitive impairment in children. Addressing these concerns involving As pollution requires a clear understanding of the factors that determine where groundwater As is present and how it will change over time. In this work, I conduct interdisciplinary, transformative, research that merges environmental chemistry and biogeochemistry, satellite remote-sensing and geospatial analysis, data science and machine learning, and public health. My goal is to [1] identify the mechanisms that link key environmental conditions to As mobilization and toxicity in groundwater; [2] accurately predicts groundwater As levels and heterogeneity across scales using solely remotely sensed data of Earth’s surface features; [3] effectively scale groundwater As concentrations across broader domains without the need to collect direct field measurements; [4] improve our ability to evaluate populations at risk of chronic As exposure in vulnerable areas and identify safe drinking water sources; and [5] forecast groundwater As concentrations under future climate and landscape scenarios.
Understanding Arsenic Contamination in Rice Grown by
Small-Scale Producers in South and Southeast Asia
Rice is the single most important source of subsistence and economic livelihood for 150 million small-scale rice farmers in S-SE Asia, many of whom suffer from chronic health effects due to the consumption of rice with poor nutritional quality and dangerous levels of arsenic (As). There is, however, a dearth of scientific understanding of the environmental conditions that drive As mobilization from soils and its uptake by rice that is urgently needed to combat this staggering public health crisis and sustain economic longevity for these farmers. Knowledge of improved farming practices that enable sustainable rice yields, improve rice nutritional value, and lower As toxicity remain unclear to date, while a lack of scalable research that can help farmers implement new management strategies has not yet been developed. As the newest of my research areas, the goal of this work is to investigate the linkages between As mobility in the environment and toxicity levels in rice, including the synergetic effects of climate (temperature and rainfall), surface hydrology (soil-saturation from flooding), and soil fertility (via the cycling of iron and zinc). I seek to improve understanding of the key climate and environmental drivers of As levels and variability in rice grown by farmers in S-SE Asia; (2) to link this understanding with high-resolution, remotely-sensed, geospatial data of local climate and Earth’s surface features to develop scalable prediction models of rice-As contamination; and to (3) use this knowledge to inform strategies that lower rice-As levels while increasing rice nutritional value and yields.
Carbon Biogeochemistry of Shallow Groundwater Entering Arctic Coastal Waters
The fate and transport of carbon from land to Arctic coastal waters is gaining attention since warming is mobilizing global stores of organic matter in high latitude soils and permafrost. Inputs of terrestrial groundwater to coastal waters may be a significant component of the contemporary carbon cycle, and provide a critical source of energy for microorganisms and higher trophic level activity. And yet, the role of coastal groundwater remains unclear across the pan-Arctic. In this research, I seek to understand how much and in what forms organic carbon in terrestrial groundwater is transported to lagoons along the eastern Alaska Beaufort Sea coast. My research approach includes quantifying concentrations of dissolved carbon and inorganic nutrients (e.g., DOC, DON, TDN, NO3, NH4, PO4), modeling groundwater discharge (using the Rn isotopic tracer), mapping the chemical composition of organic carbon (CDOM and FTICR-MS), and estimating the susceptibility of groundwater organic carbon to microbial degradation (e.g., through bioavailable DOC experiments). I use stable and radiocarbon isotopic tracers (δ13C and Δ14C) to identify the sources of groundwater carbon from different soil layers. Isotopic δ13C and Δ14C analysis coupled with serial thermal oxidation (Ramped PyrOx) of dissolved organic carbon in groundwater, river water, and lagoon water was also used to further elucidate potential carbon sources in coastal waters. My initial studies have demonstrated that contemporary groundwater export is important for coastal ecological and biogeochemical processes in Arctic coastal waters and may play an even more prominent role in the future as warming enhances subsurface flow and organic carbon inputs from thawing permafrost.
Linking Watershed Landscape Characteristics and the Biogeochemistry of Rivers across Geographical Space and Catchment Size in the Arctic
Rivers are essential to coastal ecosystem function and drive biogeochemical reactions relevant to global carbon cycling, yet our understanding of the role of river inputs is limited in many remote regions of the Arctic. In this research, I seek to develop new understanding of the relationships between watershed characteristics and the biogeochemistry of rivers draining into coastal waters of the Arctic. This work is especially important in light of warming, which is changing the nature of the Arctic hydrologic cycle and the stability of carbon in previously frozen permafrost. Both will cause major shifts in the transport and fate of riverine carbon in the coastal ocean. My initial studies included quantifying relationships between watershed landscape features (e.g., watershed slope and soil organic carbon coverage) and concentrations of dissolved organic carbon and nitrogen (DOC and DON) and inorganic nitrate (NO3) from pan-Arctic rivers that differ markedly in their size and geographic location. I found that patterns in watershed slope are fundamentally linked to variations in the amounts of soil organic matter and nutrients. I used these relationships to predict riverine carbon and nutrient concentrations, which were then paired with modeled discharge data to estimate annual fluxes from rivers on the Eurasian side of the Arctic as well as the North Slope of Alaska in data-poor regions. These studies reveal that watershed slope is a promising metric for estimating quantities of dissolved carbon in Arctic rivers without direct field measurements, thus allowing for better estimation of watershed carbon export to the Arctic Ocean. Tracking long-term changes in these relationships may help us identify the impacts of thawing permafrost and associated shifts in hydrology as the Arctic warms. My current research is this area involves a closer examination of how groundwater spring inputs and surface watershed characteristics drive the carbon biogeochemistry of the Canning River in Alaska, and ultimately what impact they have on the ecological functioning and biogeochemical reactions of their receiving coastal waters.
Seasonal Changes in the Carbon Biogeochemistry of Coastal Lagoon Ecosystems along the Eastern Alaskan Beaufort Sea Coast
Seasonality is a defining feature of the physicochemical environment in Arctic coastal regions, but fundamental understanding of temporal patterns in dissolved carbon and nutrients within productive and highly valued estuarine ecosystems in the Arctic are lacking to date. In this research, I investigate how seasonal changes in freshwater inflow, sea ice dynamics, and land-ocean connectivity affect the quantities and composition of dissolved organic matter (DOC, C:N, and CDOM) in lagoons along the eastern Alaskan Beaufort Sea coast. This investigation was conducted during three seasonal transitionary phases of the coastal Arctic: full coastal ice cover (April), riverine freshet and coastal ice break-up (late June), and the open water period (August). The results of initial and ongoing studies reveal that [i] lagoon dissolved organic matter in the spring is strongly influenced by riverine inputs that inundate the entire Beaufort Sea coastline; [ii] the chemical carbon composition of coastal waters during the summer reflects variability in both runoff from land and mixing from ocean water exchange; and [iii] local inputs of benthic material and/or the degradation of particulate organic matter retained in the water column are important contributions to the winter carbon pool. Across all seasons, dissolved carbon composition correlated with the composition of microbial communities, suggesting interaction between organic carbon quantities and the primary consumers of this material. These patterns in coastal carbon reflect distinct seasonal transitions in ice-coverage, runoff from land, water column stratification, and connectivity with the open ocean that are inherently coupled to dynamic changes in the sources and composition of biogeochemical materials in Arctic lagoons.
Characterizing the Biogeochemistry of Eroding Soils along the Northern Alaskan Coastline
Coastal erosion is prevalent across the northern coast of Alaska primarily due to thawing permafrost and increased exposure to wave action during the ice-free season. Eroding coastal soils are recognized as a potentially significant source of organic carbon fueling biogeochemical reactions and ecosystem productivity in near-shore waters of the Arctic. However, the relationships between eroding coastal material and the biogeochemistry of Arctic coastal waters remains uncertain, thus limiting our understanding of how coastal erosion will alter coastal ecosystem structure, function, and carbon cycling. The goal of this collaborative work is to quantify fluxes of carbon, nitrogen, and phosphorus from eroding soils as well as examine the degradability of this material as it mixes with nearshore marine waters. In addition, these efforts include quantifying concentrations of carbon, nitrogen, and stable and radiocarbon isotopes (δ13C and Δ14C) of soils in deep permafrost along the coast to identify specific soil-layer sources that may have a disproportionate impact on biogeochemical reactions of their associated coastal waters.
