Browsing by Author "West-Mack, Deborah E."

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Inflow Dynamics And Potential Water Quality Improvement in Lake McCarrons
    (St. Anthony Falls Laboratory, 2000-09) West-Mack, Deborah E.; Stefan, Heinz G.
    Lake McCarrons in Roseville, Minnesota, displays signs of anthropogenic eutrophication. To increase its summer transparency, different approaches/actions have been considered. A wetland system designed to remove phosphorus from the watershed surface runoff into the lake was installed and went into operation in 1985. Its performance has been described in reports by Oberts and Osgood (1988) and the Metropolitan Council Environmental Services (MCES, 1997). Other reduction techniques for primary productivity can be considered. There is also some question about the effect that the wetland system has had on inflow water temperatures. By exposing the tributary water to the atmosphere, a wetland may cause a warming of the tributary water, which is then more likely to enter the surface mixed-layer of a stratified lake in summer. In the surface mixed layer, light can be plentiful, and the phosphorus in the inflow may stimulate 'increased algae growth. The Executive Summary of the MCES (1997) report ends with this statement: "Because of the amount of polluting material discharged into the lake over the past decades, lake improvement will be difficult and expensive. The MWTS has been helpful over the past 12 years in reducing net inputs to the lake, but this study has shown that the system is decreasing the effectiveness and may be directing inflow to a limited volume of the lake above the thermocline. Possible approaches to lake improvement include chemical treatment of the lake andlor inflows; rerouting inflow below the thennocline; whole or partial lake mlxmg; and attention to the management changes noted above for the MWTS to improve perfonnance. "In this report we shall address some of these issues.
  • Thumbnail Image
    Item
    Simulation of Water Quality and Primary Productivity Control Strategies for Lake McCarrons
    (St. Anthony Falls Laboratory, 2000-07) West-Mack, Deborah E.; Stefan, Heinz G.
    A one~dimensionallake water quality model, MINLAKE98, was calibrated to simulate water temperature, dissolved oxygen, total phosphorus and chlorophyll~a in Lake McCarrons, a lake with 0.33 km2 surface area and 17.3 m maximum depth located in Roseville, MN. To improve the summer water quality of the lake, several management options have been considered. The potential effects of five of these management options were simulated using the model calibrated for 1995 and 1996 inflow and weather conditions. The model projected that total inflow diversion during the summer, phosphorus treatment of the inflow during the summer and reduction of phosphorus release from the anoxic sediments during the summer have all only a minor effect on phytoplankton standing crops in the lake. Phosphorus removal (precipitation) after ice~out (before the growing season) and artificial deepening of the surface mixed layer to 8 m or more were projected to give a significant (more than 50%) reduction in phytoplankton standing crop.