Research |
Dr. Hammerschmidt earned a Ph.D. in oceanography from the University of Connecticut in 2005, and was a Postdoctoral Scholar at the Woods Hole Oceanographic Institution prior to joining Wright State University as an assistant professor in September 2007. His research is focused on developing a quantitative understanding of the biological, chemical, and physical mechanisms and processes that affect the transport, transformation, and fate of mercury and other trace metals in the environment. His recent and on-going studies are examining the biogeochemistry of mercury and methylmercury in arctic and temperate watersheds, marine systems (coastal and open ocean), and the atmosphere.
On-going major research projects include the following:
GEOTRACES Intercalibration of Collection, Handling and Analysis Methods for Mercury Species in Seawater (Supported by NSF-Ocean Sciences). Collaborative project with Carl Lamborg (Woods Hole Oceanographic Institution), Rob Mason (University of Connecticut), and Gary Gill (Pacific Northwest National Laboratory). August 2008−August 2010.
This collaborative project is testing old ways and developing new methods to ensure that oceanographic mercury (Hg) data is of the highest quality. Accurate measurements of total mercury and mercury species in seawater are challenging because concentrations are very low and potential sources of contamination are ubiquitous and can be ruinous. Total Hg is commonly about 1 picomolar (~ 200 parts per quadrillion) in the mixed layer of the ocean and individual species, such as methylmercury and dimethylmercury, are much less. This means that we need to collect and analyze samples with sensitive equipment and methods that do not contaminate the samples. Our four research laboratories are vetting methods used commonly to collect, handle, and analyze samples for Hg species in seawater ahead of the U.S. GEOTRACES oceanographic cruises that will begin in 2010. This study has included laboratory testing of methods, intercalibration with other Hg researchers worldwide, and participation in the 2008 intercalibration cruise in the North Atlantic (WHOI and UConn) and the 2009 intercalibration cruise between Honolulu and San Diego in the North Pacific (Wright State and PNNL). This work is important because it will ensure that results from different research groups are accurate and therefore useful for broadening our knowledge of the cycling of this toxic element in the ocean.
Vertical and Horizontal Distributions of Mercury Species in the South Atlantic Ocean (Supported by NSF-Ocean Sciences [to Lamborg] and Wright State University). Collaborative project with Carl Lamborg (Woods Hole Oceanographic Institution). November 2007−present.
There is limited knowledge of the distribution of mercury species in the ocean. This research is examining the longitudinal and vertical distributions of mercury species along a transect of the South Atlantic Ocean, based on a 30-day, trans-Atlantic cruise that we took aboard the R/V Knorr from Fortaleza, Brazil, to Walvis Bay, Namibia, in late 2007 (Mak Saito, chief scientist). The primary goal of the cruise was to determine the distribution and speciation of several trace metals that influence the productivity and health of the ocean, namely iron, cobalt, zinc, cadmium, and mercury. The cruise track included coastal, gyre, and upwelling regions of the South Atlantic, with seawater collected for Hg analysis from about 10 stations spanning the western and eastern basins (vertical profiles to 5000 m), as well as additional stations near the Benguela Current (western Africa), which results in upwelling of deep ocean water and associated potential changes in the speciation, transformation (e.g., methylation of Hg), and biological uptake of dissolved metals. We are currently analyzing the ~400 water samples that were collected during the cruise.
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| Stations in the South Atlantic Ocean where seawater was sampled for Hg analysis
in November–December 2007. |
Mercury Biogeochemistry on the Continental Shelf and Slope (Supported by NSF-Ocean Sciences). Collaborative study with Bill Fitzgerald (University of Connecticut). May 2008−April 2011.
Methylmercury is the form of mercury (Hg) that bioaccumulates and biomagnifies in marine food webs, especially piscivorous fish, and represents the primary human health concern related to mercury in the environment. Most fish consumed by humans are of marine origin, and the coastal zone, including biologically productive upwelling regions, is the major source of marine fish productivity. Unfortunately, little is known about the sources and cycling of methylmercury in marine systems, especially the important continental shelf regions. Benthic Hg methylation on the continental shelf and slope is a potentially significant contributor of methylmercury to the marine environment, including biota and the open ocean. Thus, and given the limited information and knowledge regarding Hg distributions and biogeochemistry in shelf sediments and waters, we are conducting a three-year investigation that is focused on processes and reactions affecting the cycling of methylmercury in sediments and waters over a broad region of the shelf and slope of the northwestern Atlantic Ocean. This study includes sampling of multiple environmental matrixes for analysis of Hg and mercury species (methylmercury, dimethylmercury, elemental Hg): water, suspended particles, sediment, sediment pore fluids, and zooplankton. This descriptive component is complemented by mechanistic studies that are examining 1) factors affecting the sediment-water exchange of methylmercury, 2) the identity of microorganisms that produce and demethylate methylmercury in sediments, 3) bioaccumulation of methylmercury in planktonic food webs, 4) geochemical factors affecting net production of methylmercury in sediments, and 5) photochemical reactions that demethylate mercury and result in it being less available for uptake by organisms. These measurements and experiments are focused around three 11-day oceanographic cruises (one each in 2008, 2009, and 2010) in the northwest Atlantic Ocean that have provided a platform for student research and involvement. On the 2009 cruise, for example, nine of the 13 science party members were students.
Wright State students have produced real-time blogs of their at-sea experiences and science:
GEOTRACES Atlantic Section: Mercury Speciation Along a Zonal Section of the North Atlantic (Supported by NSF-Ocean Sciences). Collaborative investigation with Carl Lamborg (Woods Hole Oceanographic Institution). December 2009–December 2011.
This study continues the strong collaboration between the Wright State and WHOI mercury labs that extends from our GEOTRACES intercalibration research. This investigation will be based on a ~50-d cruise in the North Atlantic Ocean between Woods Hole, Massachusetts, USA, and Lisbon, Portugal (black “USA” track in North Atlantic on map below). We will be sampling water, from the surface to seafloor, at about 20 stations along this transect in Fall 2010 and analyzing the seawater for total Hg, methylmercury, dimethylmercury, elemental Hg, and, at some locations, mercury on suspended and sinking particles. These efforts will provided us with an unprecedented view of the distribution of mercury species in the ocean that will complement our on-going work in the South Atlantic.
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| Proposed GEOTRACES cruise tracks, lead by different nations, in the Atlantic Ocean. Map is courtesy
of GEOTRACES Program. Information on the GEOTRACES program can be found at www.geotraces.org |
Field verification of factors controlling nickel bioavailability in sediments (Supported by Nickel Producers Environmental Research Association). Collaborative project with Allen Burton (University of Michigan). March 2009–March 2010.
This project complements an on-going laboratory study, being conducted by Chris Ingersoll’s group at the U.S. Geological Survey in Columbia, Missouri, that is testing the toxicity of sedimentary nickel (Ni) to a suite of aquatic organisms. The laboratory investigation employs Ni-amended sediments that have a broad and contrasting range of physicochemical characteristics that are suspected to influence the bioavailability of Ni, namely iron oxyhydroxides, acid-voltile sulfides, and organic matter. Here, Burton and Hammerschmidt are extending the laboratory results to “real-world” conditions in field. Our research involves the in situ geochemistry and toxicity of Ni to benthic macroinvertebrates in caged exposures. The outcome of this work will be development of new models that better predict the bioavailability of Ni to aquatic organisms and thereby help protect ecosystem quality.
Effects of eutrophication on mercurybiomagnification in stream food webs (Supported by U.S. EPA). Collaborative study with Jim Oris (Miami University), David Raikow (U.S. EPA), David Walters (USGS). January 2008–May 2010.
The objective of this study is to determine whether eutrophication can influence methylmercury bioaccumulation in stream ecosystems. Specifically, we are testing the hypothesis that eutrophication reduces MeHg uptake in stream food webs. This hypothesis is being tested experimentally with 16, 140-L oval recirculating stream tanks containing water, periphyton, suspended algae, leaf packs, snails, amphipods, and clams. Levels of nutrients and methylmercury added to the tanks are kept constant among all tanks and four different levels of primary productivity are established by varying light intensity under a bank of lamps. Preliminary results from this on-going work suggest that there are differences in methylmercury accumulation from resource to consumer and consumer-type across the broad productivity gradient of this study.
Dr. Hammerschmidt is currently advising several students:
- Lisa Romas. Lisa is a 2008 graduate of St. Lawrence University (B.S., biology) in upstate New York, and joined the Hammerschmidt lab in June of that year. Lisa has participated in two major oceanographic cruises as part of her M.S. (Earth Sciences) thesis research that is focused on understanding the functional identity of microorganisms that produce and demethylate methylmercury in sediments on the continental shelf and slope. Lisa plans to work as an environmental consultant after graduating in June 2010.
- Melissa Tabatchnick. Melissa is 2008 graduate of Virginia Tech, where she majored in biology. Melissa joined Hammerschmidt’s group in September 2008 and is pursuing a M.S. degree in Earth Sciences. Melissa enjoys going to sea, but her thesis research is based on terra firma—it is focused on the soil-tree cycling of methylmercury, which appears to be an important factor affecting the exposure of terrestrial organisms to methylmercury. Melissa plans to attend medical school after graduating in June 2010.
- Avani Naik. Avani is a 2008 graduate of the University of Michigan, Department of Geological Sciences, and joined Hammerschmidt’s lab in September 2008. Her M.S. (Earth Sciences) thesis research is examining the effect of land use on cycling and transport of methylmercury, mercury, and other trace metals in three Ohio rivers. Avani is undecided whether she will work as an environmental consultant or pursue a Ph.D. after graduation.
- Matt Konkler. Matt graduated in December 2008 from Muskingum College with a B.S. in Environmental Science and minors in biology and geology. He joined the Hammerschmidt lab in September 2009 and is pursuing a M.S. in Earth Sciences. Matt’s thesis research will be focused on mercury biogeochemistry.
- Katlin Bowman. Katlin is an undergraduate Honors Student in the Department of Earth & Environmental Sciences. Katlin won the Ohio State Science Fair as a high school student, and she has worked as a full-time undergraduate research assistant in Hammerschmidt’s lab since the middle of her sophomore year. She has worked on several projects, including participation in multiple oceanographic cruises, and is conducting undergraduate thesis research examining photodecomposition of methylmercury in seawater. Katlin will graduate in June 2010 and plans to pursue a graduate degree.
- Robbie Weller. Robbie is an undergraduate Honors Student majoring in biology at Wright State, and has been working as a full-time undergraduate research assistant in Hammerschmidt’s lab since August 2009. Robbie assists with many of the chemical analyses in the lab and is responsible for establishing and maintaining our new atmospheric mercury deposition collector and weather station. Robbie anticipates graduation in June 2011.
- Dr. Geralinde Nogaro. Geraldine is a postdoctoral research associate in the Department of Earth & Environmental Sciences, and she works closely with Hammerschmidt and his students. Geraldine received her Ph.D. in Aquatic Ecology in 2007 from the University of Lyon 1 (Lyon, France), and was a postdoc at CEMAGREF of Lyon prior to her joining the EES Department. Her research is focused on nutrient and biogeochemical processes in aquatic environments, including the role of bioturbation on these processes, which has complemented our investigations of benthic mercury cycling.
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| Wright State Mercury Lab (left to right, October 2009): Melissa Tabatchnick, Katlin Bowman, Matt Konkler, Geraldine Nogaro, Chad Hammerschmidt, Lisa Romas, Robbie Weller. Not pictured: Avani Naik. |
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