Minnesota Water Resources Conference - Water Resources Center ...

Concurrent Sessions IV 10:00–11:30
Track E: Lakes
BOOK OF ABSTRACTS
Wednesday, Tuesday, October 24 28 23
Predicting Phosphorus Releases from Lake Sediments
Sergei Katsev, University of Minnesota, Duluth, skatsev@d.umn.edu; and Maria Dittrich, Swiss Institute for Environmental
Science and Technology (EAWAG)
Phosphorus is typically released from lake sediments when oxygen in the overlying water is depleted during
summer stratification. These releases are traditionally associated with the reductive dissolution of sediment
Fe oxyhydroxides to which phosphorus is adsorbed. Nevertheless, past restoration activities demonstrated
that long-term phosphorus retention is often unimproved when oxygen is artificially injected into the bottom
waters. Using Lake Sempach (Switzerland) as an example, and with the help of diagenetic reaction-transport
modeling, we analyze factors that control sediment phosphorus fluxes on longer-than-seasonal time scales. The
analysis leads to a reevaluation of the classical “oxygen-iron-phosphorus” paradigm. Restoration measures, such
as artificial oxygenation, alum deposition, or reduction of external P load, depend on the balance of organic
matter, oxygen, and Fe oxyhydroxide fluxes, rather than on their absolute values. Biogeochemical cycling of
phosphorus in the anoxic sediment layers is important, and the measures effectiveness may vary with time
scale.
Establishing Statewide Nutrient Criteria Using a Stochastic Modeling Approach
Mark Deutschman, Houston Engineering, Inc., mdeutschman@houstonengineeringinc.com; Wesley Saunders-Pearce, Houston
Engineering, Inc.; Brennon Schaefer, Houston Engineering, Inc.; and Michael Ell, North Dakota Department of Health
In 1998, the U.S. Environmental Protection Agency (EPA) published the National Strategy for the Development
of Regional Nutrient Criteria (i.e., the National Strategy). States are now required by EPA to develop nutrient
criteria protective of the beneficial uses of lakes, rivers and wetlands. Because of a lack of water quality data
for reference lakes, North Dakota is using a unique approach to establish nutrient criteria for their lakes and
reservoirs. This presentation will focus on the development and use of regionalized stochastic loading and
receiving water models to establish nutrient criteria, where environmental variability and uncertainty are
explicitly quantified. The approach also has broad applicable to the development of TMDLs.
A View from Space: Spatial and Temporal Water Clarity Trends of Minnesota 10,000 Lakes
Leif Olmanson, University of Minnesota, olman002@umn.edu; Marvin Bauer, University of Minnesota; and Patrick Brezonik,
University of Minnesota
Landsat imagery was used to create a 20-year comprehensive water clarity database for the ~1985, ~1990, ~1995,
~2000 and ~2005 time periods of Minnesota’s 10,000 lakes. Analysis of the database indicates that lake clarity
has strong geographic patterns in Minnesota; lakes in the south and southwest have low clarity, and lakes in
the north and northeast tend to have the highest clarity. Mean water clarity in central and northern Minnesota
remained stable from 1985 to 2005 while decreasing water clarity trends were detected in southern Minnesota,
where agriculture is the predominant land use. Further statistical analyses of the database, in conjunction with
demographic, morphometric and land use data, will be used to describe temporal and spatial water clarity
trends. Results of this analysis are expected to aid local and state lake managers to make informed decisions
about development policy and improve the management of lake resources.
Minnesota Water Resources Conference, October 27–28, 2008 66