Major Research Projects

Project Title: Development of a Suitable Method for the Measurement of the Dry Deposition of Elemental Mercury and Reactive Gaseous Mercury to Coastal Ecosystems Sponsor: NOAA CICEET program Co-PI's: Jim Edson, Marine Sciences, and David Miller, Natural Resource Management and Engineering

Mercury (Hg) biogeochemical cycling at the Earth’s surface involves a strong interaction between the atmosphere and the biosphere and Hg is continuously deposited as both wet and dry deposition. The dry deposition of gaseous ionic Hg compounds, which are collectively termed reactive gaseous Hg (RGHg), has recently been shown to be as important in many environments, rivaling that of wet deposition. Therefore, the development of techniques to estimate the dry deposition of Hg, as both Hg⁰ and RGHg, and primarily for the gas phase, is clearly an important scientific need and challenge. The current research will address this need by modifying an existing relaxed eddy accumulation (REA) system, developed for Hg⁰ at the University of Connecticut in the NRME Department, so that simultaneous measurements of both Hg⁰ and RGHg can be made. The system will be tested within the laboratory and outside at the University of Connecticut (Avery Point) and finally deployed for a field campaign at the National Estuarine Research Reserve (NERR) site in Narragansett Bay.

Project Title: Air-Sea Exchange and Boundary Layer Chemistry of Mercury over the Open Ocean. Sponsor: NSF Chemical Oceanography; 9/07 - 9/10

It is hypothesized that gas evasion of Hg⁰ from the ocean surface is the primary sink for ocean Hg, and is an important part of the global Hg cycle. However, these conclusions are based on scant observation and these notions cannot be properly tested using computer models because of the data gaps. Therefore this project is designed to address these issues by examining factors influencing air-sea exchange of mercury and its seasonal variability in the North Atlantic, in the vicinity of Bermuda (using the Bermuda air sampling tower at Tudor Hill and cruises to the BATS site) and South Atlantic (using studies around and at Cape Point, South Africa). The major objectives are: 1) to examine the variation in atmospheric and surface ocean Hg speciation in conjunction with ancillary measurements to allow assessment of the importance of various mechanisms whereby Hg^II can be reduced in seawater, and Hg⁰ oxidized in water and air; 2) to use this information to develop a more accurate assessment of the factors controlling the seasonal variability in ocean gas exchange of Hg⁰, and to provide better constrained estimates of the fluxes of Hg⁰ and Hg^II at the air-sea interface; 3) to perform controlled incubation experiments to examine the various redox transformations in surface waters under controlled conditions; and 4) to use the data generated to constrain and improve ocean and global Hg models, and to incorporate these findings into model simulations using the Harvard University GEOS-Chem modeling framework. To achieve these objectives, atmospheric and ocean water column measurements will be made at the two locations. Additionally, incubation experiments will be done to investigate further the important processes in the redox transformations of Hg in the boundary layer and ocean surface waters. Atmospheric samples are currently being collected at Cape Point and the first trip to Bermuda will occur in late spring/early summer 2008.

Mercury Methylation in the Coastal Zone

Project Title: Investigating the importance of the coastal zone as a source of methylmercury to the ocean. Sponsor: NSF Chemical Oceanography

This project is a collaboration with Dr Cindy Gilmour of the Smithsonian Environmental Research Center (SERC) in Maryland, who is a co-PI on the project. The rationale for the project is the hypothesis that the coastal zone may be an important location for net methylmercury (MeHg) production and that this methylation may be an important source of MeHg to ocean fish. It is not known to what extent net mercury (Hg) methylation in the coastal zone is a source of methylmercury (MeHg) to marine waters and ocean fish. Certainly, there is evidence that Hg m md coastal sediments and that the transformation occurs at signific ant rates. However, the reverse reaction, MeHg demethylation is also occurring and the relative formation rates determine the overall net production of MeHg. The project is in its second year and three cruises have been completed within the Chesapeake Bay and on the Shelf off the Bay mouth (figure shows sample locations). Cruises were completed aboard the Cape Hatteras and the Cape Henlopen. Two cruises will be Sediment samples are collected using a box corer which is subsampled for chemical measurement and for the microbial incubation experiments, as shown in the figure. Estimates of the instantaneous methylation and demethylation rates are made by injecting dissolved ¹⁹⁹Hg and CH₃²⁰¹Hg spikes into intact sediment cores followed by short incubations (2-4 hours on the cruises). Methylation is assessed by measuring formation of the end-product, CH₃Hg, while demethylation is measured through loss of substrate. Other microbial activity measurements have included CO2 and CH4 production and sulfate-reduction. Geochemical measurements (other than Hg and CH₃Hg) that have been made or samples collected include pH, anions, Fe, Mn and sulfide in sediment and porewaters, and porosity, bulk density, organic matter content, acid volatile sulfide, chromium reducible sulfide, total reduced sulfide, and Fe(II)/Fe(III) in sediments. Sediment cores are in the process of being analyzed for Hg, CH₃Hg, Fe, Mn, C, and S species. In addition to sediment samples, water samples were also collected and mercury transformation rate measurements (oxidation/reduction and methylation/demethylation) were also done in the water column.

Mercury in the South African Environment

A three year study funded through the NSF International Program - "Developing Global Scientists and Engineers through the Study of Mercury Environmental Issues in Southern Africa" - will provide the opportunity for two graduate and two undergraduate students each year to participate in a 6 week field program in South Africa. The students will design their own projects that will be coordinated with on-going studies in South Africa that have been initiated by the South African Mercury Assessment (SAMA) program. Estimates of mercury emissions from anthropogenic sources suggest that South Africa is an important contributor to Hg in the Southern Hemisphere as it gains most of its energy from coal burning, and has important ferrous and non-ferrous metal production. In addition, artisanal gold-mining using Hg, and biomass burning are potentially important Hg sources. The venture will build on collaborations already initiated with Dr Joy Leaner of the council for Scientific and Industrial Research (CSIR) in South Africa, and with other collaborators at South African universities (University of Stellenbosch, University of Kwa-Zulu Natal; and the University of Witwatersrand), and will introduce and allow coordination betweenstudents from both countries. The first field tripis planned for Summer 2007 and will include studies of atmospheric Hg, Hg in water, sediment and biota, and historical Hg deposition, which will be determined from dated sediment cores. The water column and sediment studies will include examination of Hg speciation and methylation and demethylation. An atmospheric sampling site will be set up at Cape Point, South Africa to measure atmospheric Hg speciation and Hg concentrations in deposition. Studies in South Africa will focus on both remote and impacted locations. This work will build on the results of preliminary studies conducted in 2006.

Mercury Bioaccumulation and Trophic Transfer in the Penobscot River, Maine

The research is focused on studying trophic dynamics for mercury (Hg) and methylmercury (MeHg) in the Penobscot River, in Maine, USA, which is a system that has been contaminated with mercury by industrial sources. The primary objective of this research are to document the accumulation of Hg and MeHg from surface waters of the river/estuary into representative phytoplankton and zooplankton species, and to interpret the results through the calculation of bioaccumulation factors. The trophic transfer of the Hg and MeHg in phytoplankton to zooplankton, both copepods and ciliates representative of this environment, will be examined in detail. Ancillary measurements besides Hg will allow the uptake of hg and MeHg to be related to environmental variables. Finally, the study will document if there are any effects of the Hg and MeHg in the phytoplankton on the growth and reproductive health of the zooplankton organisms. Samples were collected in May 2007 and the various experiments are underway.

Completed Projects

The METAALICUS Project

Project Title: Metaalicus: A whole-watershed, stable isotope study of the microbial mechanisms of net methylmercury production. Sponsor: NSF Ecosystem Studies, subcontracted through SERC.

Our research group has a small part in the multi-investigator METAALICUS project which is taking place in the Experimental Lakes Area (ELA) in northern Ontario, Canada. This effort is in collaboration with Cindy Gilmour of SERC, Andrew Heyes of the University of Maryland and Eric Roden of the University of Wisconsin, and is currently funded through NSF. Involvement was initiated through two EPA STAR grants, both in collaboration with Cindy Gilmour. The study location is Lake 658 in the ELA which is being dosed with three different mercury isotopes which are being added, respectively, to the lake surface, an associated wetland and the upland (see figure). The studies have focused on the factors influencing mercury methylation in sediments, and the surrounding uplands and wetlands. The role of mercury speciation, as influenced by sulfide and DOC, and the importance of bacterial community structure in determining methylation rate are being studied. Theses studies are also using the new approaches of examining mercury methylation and demethylation rates using stable isotopes. The rate of methylation of the mercury added directly to the lake is rapid as the presence of MeHg isotope was detected in the bottom water of the lake within two months of the first addition. Both field and laboratory studies are being done in order to understand the dynamics of mercury methylation in lake sediments, wetland peat and upland soils, and the factors controlling mercury bioavailability to the methylating bacteria.

Mercury in the San Francisco Bay Delta Region

Project Title: Evaluation of mercury transformation and trophic transfer in the San Francisco Bay/Delta: Identifying critical processes for the Ecosystem Restoration Program. Sponsor: CALFED Ecosystem Restoration Program, subcontract through the USGS, Menlo Park.

The project is a multi-investigator endeavor involving the USGS (Menlo Park, CA), the primary contracting agency with CALFED, the State University of New York (Stony Brook, NY) and the University of Connecticut. The project is investigating the relative importance of biogeochemical processes as apposed to changes in food chain length and structure in influencing MeHg production and in determining the concentration of MeHg in predatory fish in the San Francisco Bay Delta region. The two study regions in the San Francisco delta region are Frank's Tract in the central-delta (low Hg) and the Cosumnes River tributary (high Hg) (see Figure) and the study is contrasting both trends in biota Hg levels, and Hg biogeo-chemistry. The study is focused mainly on field investigations of the primary biogeochemical transformations of Hg and MeHg in the water column and sediment in conjunction with measurement of Hg and MeHg and stable isotopes (C, N, S) in all levels of the food chain. The results are being incorporated into a model to further probe the controlling factors over MeHg levels in fish in these dynamic systems. Preliminary results suggest that while the levels of total Hg in sediments from both regions fall in a similar range, distribution coefficients (Kd's) are much lower for the Consumnes River and therefore this may be one important factor contributing to the higher overall MeHg levels within this system. For both sites, there is a relationship between sediment organic matter and Hg levels, but the relationships are no the same. For the same organic content, the Consumes River has a much higher Hg content relative to Frank's Tract. Overall, there appears to be a reasonable relationship between the amount of available Hg in porewater; the overall higher MeHg within the system and the MeHg levels in biota, as all three appear to be highest in the Consumnes River. More data analysis is required to obtain a more picture of these preliminary observations. More results and other information on the project is available at the CALFED website.

Mercruy Methylation and Cycling in the Gulf of Mexico

Title: SGER: Assessing the impact of hurricanes on mercury biogeochemistry and methylation in the Gulf of Mexico. Sponsor: NSF Chemical Oceanography (collaborative project with the Harvard School of Public Health; D. Senn, co-PI).

This project was initiated to examine the impact of large physical disturbance on Hg methylation and cycling in a crucial coastal region, the Gulf of Mexico. Hurricanes Katrina and Rita caused intense physical mixing activity and sediment redistribution and thesechanges, in conjunction with the likely input of fresh organic matter and runoff from the terrestrial environment, could lead to enhanced Hg methylation in the offshore waters. Samples had been collected by Harvard in summer 2005 and so the project was initiated to compare and contrast these pre-hurricane data with post-hurricane collections. Samples were collected in October 2005 and another cruise will occur in Spring 2006. Samples were collected for Hg, MeHg and ancillary parameters in the water column and sediments and Hg methylation/demethylation assays were also completed, in a similar fashion to our other studies. The cruise track and sampling locations are shown in the accompanying figures.

Mercury Deposition to Bermuda: Local and Regional Contributions

Title: Mercury in the atmosphere in Bermuda. Sponsor: Bermuda Biological Station/Bermuda Government.

In response to measurements of elevated levels of Hg in fish from local and surrounding waters of Bermuda, a study was set up to investigate whether sources of Hg input were local, regional or global. A potential local source was a waste incinerator on the island and the sampling location for the initial study has been set up so that any local input from this source, compared to oceanic sources, would be measured under the correct weather conditions, especially wind direction. Samples are being collected on a weekly basis for total Hg in rainwater and on a regular sampling schedule for gaseous Hg and Hg speciation. It is anticipated that an intensive study will be completed on site in 2006 to compliment the more routine sample collections. Samplers are prepared at Uconn and then shipped tom Bermuda. After use, the samples are shipped back for analyses. The accompanying picture shows the wet deposition collector deployed at the sampling site.