Research

My group's research interests involve understanding how sulfur and iron interact in in engineered and natural systems to transform and mobilize contaminants, especially at redox interfaces. We study fundamental and practical aspects of environmental aquatic chemistry, contaminant biogeochemistry, and biological and chemical processes related to contaminant transport and transformations. Most of our work involves understanding contaminant (mercury and trace organics) interactions with the bulk elemental cycles of sulfur, iron, and carbon.  All of our projects are related to developing management strategies for water quality challenges in engineered and natural systems. We typically try to complement field or laboratory investigations with mathematical modeling. 

Currently, the three main themes of our research are the cycling of mercury and sulfur in municipal and industrial wastewater, management strategies to address mercury in aquatic sediments (external link to MPCA website),  and the impacts of sulfate on NE Minnesota water resources (external link to MPCA website, and DNR website). My research group is currently comprised of 3 MS students, and 4 undergraduate students.

Ongoing Projects

We are collaborating with power industry and mining-sector partners to remove sulfate from Flue Gas Desulfurization wastewater using a combined biological (sulfate to sulfide) and chemical precipitation (sulfide with iron) treatment system.  We have built a pilot-scale treatment system (~150 gallons) and are operating it at an industrial partner's site during the ice-free seasons.  So far we have removed 250 g of sulfur from the industrial water, but we hope to be removing ~30 g/day with the fully-operational pilot system on the way to drastically reducing the potential for sulfur emissions to surface waters.      

We collaborate with Fond du Lac Tribal college to mentor students in research methods while investigating an important resource management question facing the region:  how do different landscapes export MeHg to surface waters and what are the implications of different landscape types for Hg bioaccumulation in the food web.  In particular, we are studying how the quantity of Hg and MeHg varies in streams with homogeneous upstream landscapes, including wetlands, forested land, and ditched peat lands.  Catching odonates and collecting water samples for Hg and related chemistry.    

We are working with MPCA to understand the impacts of shallow water habitat restoration (creation of new wetlands from hardened shoreline) on mercury bioaccumulation.   We are complimenting field measurements of pre- and post- habitat restoration site conditions with mesocosm-scale investigations of the impacts of different types of carbon amendments on Hg bioavailability (MeHg production and transport) and Hg bioaccumulation (in low-level food web indicator species).     

Recent Projects

We collaborate with Fond du Lac Tribal college to mentor students in research methods while investigating an important resource management question facing the region:  how do different landscapes export MeHg to surface waters and what are the implications of different landscape types for Hg bioaccumulation in the food web.  In particular, we are studying how the quantity of Hg and MeHg varies in streams with homogeneous upstream landscapes, including wetlands, forested land, and ditched peat lands.  Catching odonates and collecting water samples for Hg and related chemistry.    

With partners from UW Madison and LaCrosse and Gustavus Adolphus college, we will be investigating the controls of Hg bioavailability and food web entry in the St. Louis River Estuary.  Building on work over the last couple years, this project will be focused on characterizing the geochemical characteristics and processes in sediment that influence how rapidly mercury is taken up into the food web. 

We study the impacts of sulfur to wild rice at both the ecological level and more detailed biogeochemistry.  Ongoing mesocosm experiments with self-perpetuating wild rice populations provide a test bed for understanding the ecological response of a sensitive aquatic plant to pertubations in loads of sulfur, carbon, and iron.  Smaller-scale, single bucket experiments allow us to probe the near-rooting surface biogeochemical processes that impact the plants' ability to take up nutrients and protect against harmful reactive substances in saturated wetland sediment.  

   

Past Projects

Working with colleagues from Gustavus Adolphus College and Toronto Scarborough, we are seeking to quantify the importance of processes that transport mercury and methylmercury across the riparian boundary in streams.  We have installed and sampled from shallow groundwater piezometers in 3 western MN watersheds with substantial agricultural influence and will compare processes with 2 forested/wetland watersheds in Northeastern MN.  Partners (from UW LaCrosse and MPCA) are also quantifying bioaccumulation rates in the 5 watersheds and the seasonal distribution of Hg loads carried by the streams.

The propose of this project is to provide a protocol for prioritizing sites in the St. Louis AOC for restoration based on site-specific bioavailability considerations. Despite large data collection efforts focused on sediment chemistry, the extent to which sediment with moderate levels of contamination is available for uptake into biota and therefore contributing to BUIs is still largely unknown. the proposed study will: (1) Evaluate the ability of existing information to support bioavailability -based assessments of BUI impairments (2) Collect and analyze targeted samples to characterize site-specific geochemical characteristics that control bioavailability (3) Recommend a protocol for prioritized BUI assessment and removal based on site-specific bioavailability considerations (4) Provide guidance on organizing and sharing data describing sediment contamination in a way that is accessible to state, federal and local agencies as well as public entities and interest groups

The extent to which total- and methyl- mercury flux from sediments in the St. Louis River Estuary contributes to water column and/or fish tissue concentrations is presently unknown. This study will make in-situ measurements of pore water and solid phase mercury and associated biogeochemical parameters and deploy chambers to quantify the flux of total- and methyl- mercury across the sediment-water interface.

The overall goals of the project are to: 1) to determine if restoration efforts utilizing navigational with dredged material is an effective strategy for reducing contaminant bioavailability during restoration at moderately contaminated areas and 2) to develop a methodology for using passive sampling devices to quantify contaminant bioavailability that can be used to evaluate restoration at other sites in the Great Lakes. This project will utilize passive sampling techniques to quantify the effects of restoration efforts in the Duluth-Superior harbor in terms of (a) pre- and post- surficial sediment contaminant availability, (b) potential for contaminant transport through habitat creation material, and (c) implications of potential ongoing sources of contamination to surficial sediment in restoration areas.

Anoxic sediment typically has a large reserve of iron in various solid phase forms in addition to that present in pore waters. As sulfide is added to sediment as a result of biological sulfate reduction, the precipitation of insoluble iron sulfide can remove sulfide from pore waters until the readily available iron is depleted. This lab study is investigating methods for characterizing the capacity of sediment to remove added sulfide from pore waters.

In order to evaluate the mechanisms of methylmercury production and release from wetlands and lakes receiving sulfate from mining on the Mesabi Iron Range, this project is undertaking an in-depth characterization of methylmercury production and the related geochemical setting at four sites (two lakes and two wetlands) in mining-impacted watersheds. Replicate sediment cores, pore water samples, and surface water samples will be collected from each lake/wetland site at various times throughout the summer and analyzed for a host of parameters including methyl mercury (total and dissolved), mercury methylation rate, sulfate, sulfide, iron, pH, and DOC.

In order to help understand whether sulfide builds up in the pore waters of sediment underlying a water column with elevated sulfate concentrations, porewater measurements of iron, sulfide, sulfate, and pH are being taken with high depth resolution (1.5cm) in sulfate amended wild rice microcosms (John Pastor). Measurements will be made at three key stages in wild rice growth (floating leaf stage, budding stage, cenessance) in the summers of 2012 and 2013. Measurements in sulfate amended mesocosms will be compared to measurements at two field sites during the summer of 2013.

The Minnesota sulfate standard includes language related to the timing of sulfate discharges to waters used for the production of wild rice. In order to understand the rates of sulfate diffusion and reaction in sediment, laboratory mesocosms from sites containing high and low organic carbon are being incubated at warm (21C) and cold (5C) temperatures while exposed to an elevated overlying water column sulfate concentration for a fixed length of time (~2months). Porewater and overlying water will be monitored to quantify the rates of diffusion into and out of sediment pore waters for sulfate and a tracer. A mathematical model will be developed and used to describe the rates of sulfate reaction and transport.

The proposed work is quantifying the bioavailability of PAHs in stormwater pond sediments and assess the extent to which the contaminants can accumulate in aquatic organisms. PAH availability is being assessed in three relevant locations related to stormwater ponds: (a) uptake to organisms in the sediments at the bottom of existing stormwater ponds, (b) release from soil particles to water during resuspension, and (c) uptake to organisms from sediments once they reach a downstream natural waterway. The study involves a combination of field sample collection and small-scale laboratory studies using stormwater ponds in the City of Duluth and St. Louis River Estuary as a pilot system.