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My research is driven by my curiosity about how human activity affects lake and river water quality, ecosystems and nutrient cycles. Aquatic resources around the world are threatened by pollution of various sorts; in order to develop sound and achievable management policies, it is critical that we first define the “natural conditions” of the particular system, quantify the human impact, and determine what are the goals and priorities for future use of that resource. The first step often requires the use of paleolimnological techniques to reconstruct prehistorical conditions in the water body. The second step may utilize existing monitoring data or may require a new monitoring program and methodology to establish the current condition of the water body. The third step, determining society's priorities and goals, is where the scientist must reach out to the non-science community and make the data, methods and conclusions accessible and meaningful to the public. I enjoy every step of this process.
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Recent projects
== I am studying silica fluxes and trapping in Lake St. Croix and Lake Pepin, two natural impoundments in the upper Mississippi River. By measuring dissolved and amorphous silica concentrations in the lake inflow, outflow, sediments and sediment porewater, my colleagues and I quantified the amount of amorphous silica production (i.e. diatom production) in each lake. We have also determined the silica trapping efficiency for each lake and how that has changed through time as the two river/lake systems became eutrophic due to human activity on the landscape. These studies have helped clarify the role that riverine impoundments - whether natural or artifical - play in the global silica cycle.
== To reconstruct the history of heavy metal pollution in the St. Croix River, my colleagues Dan Engstrom (SCWRS) and Steve Balogh (Metropolitan Council) and I collected sediment cores from Lake St. Croix and analyzed them for Hg, Pb, Ag, Cd, Cr, Zn, Mn and Fe. Our results show that metal pollution increased immediately after Euro-American settlement, most of which was from point source discharges to the river. In the early 1900s, the concentrations of some metals (e.g. Hg and Pb) became dominated by more regional, atmospheric pollutant sources. Furthermore, we have isolated the pollution impacts of the largest point source discharger, the city of Stillwater, by analyzed sediment cores upstream and downstream of the city's wastewater outfall.
== I am tangentially involved in an exciting new study using the 210Pb and 137Cs activities of sediment particles to "fingerprint" the source of sediment polluting the Minnesota and Mississippi Rivers. This new method will determine the relative importance of field erosion versus riverbank erosion (due to hydrologic changes) and thus has major implications for agriculture and environmental management.
== My colleagues Dan Engstrom, Mark Edlund and I constructed a phosphorus mass balance and sediment loading history for Lake St. Croix for the past 200 years. (European settlement was in the mid-1800s in this region.) We used a series of sediment cores from the lake bottom to measure multiple water quality proxies including diatom algae assemblages, organic matter content, sediment grain size and biogenic silica concentration, all based on chronologies developed from 210-Pb, 137-Cs and 14-C analyses. Our results showed dramatic increases in phosphorus and sediment loading over the past 100 years even though this is still considered by many to be a relatively "pristine” river. Our results were instrumental in developing the Agreement on Nutrient and Sediment Reduction in the St. Croix River Basin, which was signed by the Commissioner of the Minnesota Pollution Control Agency (MPCA) and the Secretary of the Wisconsin Department of Natural Resources in 2006 (read more on the MPCA website).
== In 2001, a group of graduate students retrieved a sediment core from Campbell Lake in northwestern Minnesota to compare the biogeochemical responses in the lake to a known series of human activities in the watershed. We presented our findings as a poster at the American Geophysical Union fall meeting in 2001.
View .pdf of the poster (3.58 MB)
Funding sources and collaborators
Department of Geology and Geophysics, University of Minnesota
St. Croix Watershed Research Station, Science Museum of Minnesota
Canon National Parks Science Scholars Program
http://www.nature.nps.gov/canonscholarships/
http://www.usa.canon.com/templatedata/pressrelease/20041111_canon_scholars.html
U.S. Department of Education, Graduate Assistance in Areas of National Need
Metropolitan Council Environmental Services
National Park Service
Minnesota Pollution Control Agency