Geo-ecolgy and the Smithsonian fellowships

Marilyn, Jess Parker, Glenn Piercey, Smithsonian Research Center, preparing to soar in a crane 40 m high, circa 1999

   

      As my career developed, I became more engaged in straight-out ecological research because stable isotope biogeochemistry was becoming increasingly accepted by the ecological community.  My goal as a stable isotope ecologist is to learn as much as I can about modern ecosystems on a global scale so that I can use that knowledge to interpret fossil ecosystems where direct observation of the plants, animals, and microbes is not possible. I have worked in most of the major biomes: deserts, temperate deciduous forests, grasslands, alpine, arctic, taiga, tundra, temperate rain forests, woodlands, freshwater wetlands, estuaries, coastal wetlands, lakes, marine ecosystems, and coral reefs. From my first forays in South Texas bays in 1974 to my last trip to Arctic Svalbard in 2015, the unity of nature in combination with all of the variables that shape ecosystems and influence their isotopic composition has been a learning experience. My work took me to almost every continent: North America, South America, Central America, Europe, Asia, Australia, and Africa, only missing out on Antarctica. Doing ecological field work internationally requires extensive preparation, sampling permit applications, import and export permits, advance planning, and being nimble on your feet when conditions change---but it is worth it all. In relationship to field work, Mat Wooller, University of Alaska, trumpeted the “Seven Ps”: “Prior preparation and planning prevent piss poor performance.”

         The term Geo-Ecology, as it pertained to my research, surfaced around 2009. For the first two-thirds of my career, the impetus for my research was primarily in sync with the biogeochemistry community, and secondarily the geochemical community. Much of my early work established isotope fractionations for certain biochemical pathways, information which proved useful for others who were interpreting isotopic measurements that were more applied to a particular problem or ecosystem. The major incentive for me to begin to concentrate more on ecology came from two fellowships (Loeb and Mellon Fellow) awarded to me by the Smithsonian Institution’s Environmental Research Center (SERC) in Maryland. I was awarded unrestricted funds to develop collaborations with Smithsonian Institution scientists at SERC, as well as to provide access to my stable isotope lab at Carnegie since the Smithsonian did not have an IRMS facility at that time.

Rhode River, Maryland, site of fish studies at SERC

Setting up a fish weir on the Rhode River

         My first collaboration was with Anson Tuck Hines, Associate Director of SERC and a fish and crab biologist. Seining for estuarine fish and other field sampling took place weekly on the Rhode River, Hines’ lab study site on the Chesapeake Bay. We measured the carbon and nitrogen isotope compositions of over 800 samples of fish, invertebrates, zooplankton, phytoplankton, and seaweeds in three Chesapeake Bay tributaries: Rhode River, Nanticoke River, and Muddy Creek. Ecologists are interested in identifying the source of primary production at the base of food webs and how it changes over space (habitats) and time. In terrestrial river systems, organic carbon that supports food webs can come from sources produced in the river-estuary system (i.e. autochthonous) or from terrestrial plant material washed in from land (i.e. allochthonous). For my first project with SERC, we determined that autochthonous sources were most important for zooplankton and the larger fish, such as the striped bass, whereas allochthonous sources influenced the diets of benthic organisms, like clams. In the Chesapeake Bay, the striped bass is an important and threatened fish species which once supported a plentiful, commercial fishery. Now the catch is strictly regulated and open only to recreational fishing.

Marilyn and Jess Parker in the crane, SERC

         With SERC plant ecologist Jess Parker, we rented a crane that took us to the tops of 30-40 meter trees to collect leaves in SERC’s temperate deciduous forest. How cool is that to be lifted high off the ground in a little bucket pointing out leaves you’d like to sample? We documented that leaves growing higher in the canopy have more positive carbon isotope values than those lower in the canopy. Our results were paired with Penn State’s results on tropical rain forests, which were used to bolster the interpretation of carbon values measured in fossil leaves. In a sedimentary deposit, leaf fragments often persist millions of years (e.g. Schweitzer et al., 2006), and their carbon isotope values serve as proxies to construct paleoenvironmental conditions such as paleo-carbon dioxide levels, temperature, or rainfall. 

         Not only did the Loeb fellowship open up doors with Smithsonian colleagues, but it provided funding for me to hire laboratory technical support, postdocs, and undergraduate and graduate interns. With all of the samples to analyze, I needed to hire a lab assistant to help out. My first choice for the position was Mat Wooller, then finishing up his Ph.D. at the University of Swansea in Wales. Mat had about a year left to finish up before you could move to the United States.  I was left with a quandary of what to do for the year gap. I ended up hiring Glenn Piercey, who had little to no direct experience with stable isotopes. Glenn’s girlfriend at the time—my current postdoc Sue Ziegler—was hoping that she and Glenn would have a chance of getting to know each other further, if he had a job in the Washington, DC, area. Hiring Glenn seemed a good way to get the Loeb projects started. Within a few months, Sue and Glenn announced their engagement, were subsequently married, and have a full life and family. I’d say this was a most successful hire on many fronts.

Glenn Piercey running the isotope instruments, 1999

         Another project that extended for many years was a collaboration with Tom Jordan, a nutrient biogeochemist. A normally taciturn man, Tom had an easy going way about him and thought carefully before beginning a project. We settled on using stable isotopes in nitrate to learn if runoff from farmer’s fertilizers were contaminating the Chesapeake Bay. This study required that I come up to speed with oxygen and nitrogen isotopes in silver nitrate—an analysis that requires strict chemical processing, running lots of standards, and keeps you on your analytical toes. Our results from years later showed that buffer zones between a farmer’s fields and the Bay worked to convert much of the fertilizer runoff into nitrogen gas, which escapes into the atmosphere.

         The Mellon Fellowship provided funding to study the effects of the waste from chicken farming on the Chesapeake Bay and environs. More on that later.