Research

The Watershed Biogeochemistry in the Anthropocene Lab studies how anthropogenic activities have altered the cycling of nutrients and contaminants through watersheds, with a focus on linked biogeochemical cycles within socioenvironmental systems. We examine the fate, transport, and transformation of these elements and compounds within and between terrestrial and aquatic ecosystems. We also evaluate the implications this has for the people and animals that live in these landscapes. Our lab uses a variety of interdisciplinary tools to address these questions including fieldwork, labwork, and data syntheses and takes place locally, nationally, and internationally. We are guided by four overarching research questions:

How does geochemical setting (e.g., geochemical properties of source material, geochemical processes) constrain the biogeochemical cycling of elements, and how is human activity altering these cycles?
When and where on the landscape do control points (hotspots and hot moments) emerge?
How does coupled elemental cycling impact the fate of individual nutrients and contaminants?
How can we use biogeochemical data to create a risk landscape that guides management, mitigation, and conservation efforts to reduce harms posed to people and wildlife?

Below are some examples of research conducted in the lab.

Implications of agricultural sulfur additions on the cycling of mercury

With the implementation of the Clean Air Act and its Amendments, sulfur deposition (i.e., acid deposition) has drastically decreased. Today, the largest source of sulfur is from agricultural activity, where sulfur is added as a pesticide/fungicide, fertilizer, soil conditioner, and nutrient carrier. For example, vineyards in Napa Valley, California use sulfur to prevent powdery mildew infection. But sulfur leaches into nearby aquatic environments, which also have elevated mercury concentrations from historical gold mining. With funding from the USDA NIFA and in collaboration with Eve Hinckley (CU Boulder), Peter Weiss (UCSC), and Nettie Calvin (UCSC), we are examining the extent to which sulfur inputs from vineyards are impacting the microbial conversion of inorganic mercury to the bioavailable and toxic form of methylmercury. We are also examining how the global sulfur cycle has changed over the past few decades, the implications this has for plant nutritional needs as well as environmental consequences, and how we can better manage sulfur for a sustainable future.

Transport and fate of mercury from illegal artisanal and small-scale gold mining activities

In the process of illegal artisanal and small-scale gold mining (ASGM), mercury is added to soil and sediment to isolate gold. This mercury-gold amalgam is then heated to create pellets of gold, releasing the mercury into the atmosphere while mercury remaining in tailings is deposited onto the landscape as mining waste. As a result, ASGM represents the largest source of global anthropogenic mercury emissions, more so than coal combustion. With funding from NSF DISES and in collaboration with Heidi Hausermann (CSU) and Richard Amankwah (UMaT Ghana), we are examining atmospheric mercury transport processes, mercury accumulation in soil, and mercury uptake in plants near ASGM activities in Ghana. We are also evaluating the resulting exposure risk for local communities. We are also continuing previous work to understand where and when there are control points for mercury deposition and mercury methylation in tropical forests and surface waters near ASGM in the Peruvian Amazon. We then use this information to determine human and wildlife exposure to mercury, as well as best practices for reducing mercury exposure risk.

Can selenium provide protection from mercury bioaccumuluation and toxicity?

Mercury is a potent neurotoxin that can impact both humans and wildlife. Selenium, while an essential nutrient, can cause deformities in organisms when present in high concentrations. However, some studies suggest that when both mercury and selenium are present at elevated levels, selenium can reduce mercury methylation, bioaccumulation, and/or toxicity. We are investigating evidence for mercury and selenium interaction at the geochemical and microbial levels, as well as at base of the food web using field data collection, field and laboratory experiments, models, and literature syntheses.