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My interests as an aquatic ecologist center around the interactions of trace elements and contaminants on the biota at the base of aquatic food webs. I have utilized several approaches and methodologies in pursuit of these interests including field work to compare contaminant dynamics across-systems, in-depth site-specific studies, laboratory and field experimentation, trace metal clean techniques, and the development of enriched stable isotope methodologies. I have worked primarily in temperate, freshwater lakes and rivers, but more recently my research includes tidal ecosystems.
My early research experiences investigated the effects of acid deposition on plankton communities in a whole lake manipulation in Northern Wisconsin supervised by Dr. Tom Frost at the University of Wisconsin's Trout Lake Station. My interests in the acid deposition studies led to research opportunities involving primary productivity, fish surveys, and zooplankton ecology as a part of the Northern Temperate Lakes Long Term Ecological Research program run by the University of Wisconsin-Madison. My participation in an intensive sampling effort of lakes across northern MN, WI, and MI (with Dr. Katherine Webster now at the University of Maine) solidified my interests in cross system comparisons in assessing the effects of contaminants and trace elements on aquatic biota.
Whereas the above research primarily investigated the effects of non-toxic inputs (e.g., sulfate, nitrate, etc.) to aquatic systems, my work on trace metals in lakes deals with the uptake and trophic transfer of potentially toxic trace elements. At Dartmouth College (with Dr. Carol Folt and Dr. Celia Chen) I helped implement a trace metal clean sampling regime across a diverse gradient of New England lakes to assess the degree of trace metal contamination in aquatic biota. Smaller scale research studied the trophic transfer of inorganic and methylmercury utilizing novel enriched stable isotope methodologies. In collaboration with Dr. Bjorn Klaue and Dr. Joel Blum (University of Michigan), we successfully tracked mercury through aquatic food webs at laboratory and mesocosm scales at environmentally realistic mercury concentrations. Important results from my mercury studies indicate that short term variability in phytoplankton abundance affects the trophic transfer of methylmercury to crustacean zooplankton.
For my post-doctoral research I joined Dr. Nicholas Fisher's laboratory at the School of Atmospheric and Marine Sciences (SoMAS) at Stony Brook University in New York. At SoMAS my research concerned the cycling and trophic transfer of trace elements in the San Francisco Bay and Delta ecosystem. In particular, our research examined the biogeochemical cycling and bioaccumulation of inorganic and methylmercury in the phytoplankton and herbivores of the freshwater, tidal Delta ecosystem. In collaboration with Dr. Robin Stewart and Dr. Mark Marvin DiPasquale (USGS scientists at Menlo Park) and Dr. Rob Mason (University of Connecticut) and Dr. Andrew Heyes (University of Maryland) I studied mercury dynamics in primary producers, crustacean herbivores, and planktivorous fish using radioisotopes of mercury. The research in New York allowed me to utilize a bioenergetic-based model developed in the Fisher lab to quantify the sources of bioaccumulation for mercury and to make predictions on mercury accumulation in the field. Additionally, we started experiments on the effects of dissolved organic carbon on the bioaccumulation of mercury and on possible interactions between mercury and selenium in aquatic biota.
Here at Lakeland College I have continued my research on trace metal dynamics in aquatic systems through the Lakeland Undergraduate Research Experience (LURE) program. In these research efforts I involve motivated, enthusiastic undergraduates each summer who tackle relevant questions in local aquatic habitats and/or the laboratory. To continue this line of research we will — ideally — set up a small laboratory in Chase Hall that has the analytical capabilities to measure environmentally relevant concentrations of mercury in water and biota.
For more information, publications stemming from the above research follow.
Karimi, R., C. Y. Chen, P. C. Pickhardt, N. S. Fisher, and C. L. Folt. 2007. Stoichiometric controls of mercury dilution by growth. Proceedings of the National Academy of Sciences of the United States of America 104:7477-7482. (PDF 769K)
Pickhardt, P. C., and N. S. Fisher. 2007. Accumulation of inorganic and methylmercury by freshwater phytoplankton in two contrasting water bodies. Environmental Science & Technology 41: 125-131. (PDF, 139K)
Pickhardt, P. C., M. Stepanova, and N. S. Fisher. 2006. Contrasting uptake routes and tissue distributions of inorganic and methylmercury in mosquitofish, Gambusia affinis, and redear sunfish, Lepomis microlophus. Environmental Toxicology & Chemistry 25: 2132-2142. (PDF, 141K)
Pickhardt, P. C., C. L. Folt, C. Y. Chen, B. Klaue, and J. D. Blum. 2005. Impacts of zooplankton composition and algal enrichment on the accumulation of organic and inorganic mercury in an experimental freshwater food web. Science of the Total Environment 339:89-101. (PDF, 349K)
Pickhardt, P. C., C. L. Folt, C. Y. Chen, B. Klaue, and J. D. Blum. 2002. Algal blooms reduce the uptake of toxic methylmercury in freshwater food webs. Proceedings of the National Academy of Sciences of the United States of America 99:4419-4423. (PDF, 110K)
Chen, C. Y., R. S. Stemberger, B. Klaue, J. D. Blum, P. C. Pickhardt, and C. L. Folt. 2000. Accumulation of heavy metals in food web components across a gradient of lakes. Limnology and Oceanography 45:1525-1536. (PDF, 126K)
Pickhardt, P. C., C. L. Folt, C. Y. Chen, B. Klaue, and J. D. Blum. Contrasting effects of algal composition and abundance on the accumulation of mercury by diaptomid copepods. In preparation
Pickhardt, P. C., C. L. Folt, C. Y. Chen, B. Klaue, and J. D. Blum. Differences in mercury accumulation by Daphnia pulex associated with algal species composition and abundance. In preparation
Pickhardt, P. C., E. Freimuth, and N. S. Fisher. The effects of organic and inorganic mercury consumption on the population dynamics of Daphnia pulex and implications for trophic transfer. In preparation
Marvin-DiPasquale, M., Stewart, A.R., Fisher, N.S., Pickhardt, P., Mason, R.P., Heyes, A. and L. Windham-Meyer. 2005a. Evaluation Of Mercury Transformations and Trophic Transfer in the San Francisco Bay/Delta: Identifying Critical Processes for the Ecosystem Restoration Program: Annual Report of Progress for Project # ERP-02-P40. Submitted to the California Bay Delta Authority (CBDA). Sacramento, CA. November 7th, 2005. Available at: http://www.delta.dfg.ca.gov
Folt, C. L., C. Y. Chen, and P. C. Pickhardt. 2002. Using plankton food web variables as indicators for the accumulation of toxic metals in fish. in S. H. Wilson and W. A. Suk, editors. Biomarkers of environmentally associated disease: Technologies, concepts, and perspectives. CRC Press/Lewis Publishers, Boca Raton.
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