A grid was generated for the western basin of Lake Superior with ... with applying
hydrodynamics to determine water-quality of the system. A model,.
PREDICTING ECOSYSTEM CHANGES IN LAKE SUPERIOR: HYDRODYNAMICS Rasika Gawde and Martin Auer Michigan Technological University, Houghton, MI 49931 Introduction
Results
Model Grid
As part of the Great Lakes Restoration Initiative (GLRI), the overarching project goal is to develop a linked hydrodynamic - water-quality – bioenergetics model with the capacity to predict responses of Lake Superior to changes in forcing conditions (e.g. meteorology, nutrient levels, food-web alterations due to invasive species, etc). The project is segmented into three parts, each concentrated on an individual model and its interactions with the other two components. Here, research efforts deal primarily with applying hydrodynamics to determine water-quality of the system. A model, Environmental Fluid Dynamics Code (EFDC), is appropriated for this purpose. The hydrodynamic model will be applied to study thermal bar development, vertical stratification, current patterns, plume migration and sediment focusing including the impact of these phenomenon on water-quality and the food-web structure in Lake Superior. The model grid establishes the spatial extent and vertical partitioning of the system being modeled. A grid was generated for the western basin of Lake Superior with cells concentrated along the Keweenaw Peninsula using the Generalized Vertical Coordinate system (vertical axis) and curvilinear, orthogonal coordinates (horizontal axis).
EFDC Inputs Forcing and boundary conditions are set up for the period over which the model will be run. Forcing conditions, primarily meteorological data, were obtained from National Data Buoy Center (NDBC), National Solar Radiation Data Base (NSRDB) and NOAA’s National Ocean Service (NOS). Boundary conditions, required only for the open-ended eastern edge, since the other three sides of the model grid are bounded by land, are defined by flow velocities obtained as output of NOAA’s Great Lakes Coastal Forecasting System (GLCFS) Nowcast model (2006 onwards).
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Thermal Structure The thermal structure of the lake is defined by the development of a thermal bar and vertical stratification. Solar radiation causes the shallow near-shore waters of a lake to heat up and form a segment of warmer water. This is held in position by a segment of colder water. The segment of warmer water gradually extends towards the center of the lake with time and ultimately results in vertical stratification.
Next, the hydrodynamic model needs to be calibrated and validated to fit vertical and horizontal temperature structures from Lake Superior. In preparation for this step, data sets from 2011 were uploaded to the modeling database facilitating visual comparison between model predictions and measured values. The simulation results can be viewed using a software, WinModel; either in a spatial scale (over the HN transect) or a temporal scale (duration of the model run).
Future Work
Measurements A rich and extensive temperature data set was developed by our project team for the 2011 sampling season for the HN transect. This includes detailed vertical temperature profiles at 11 stations along the HN transect over the April to October period. The sampling cruises were conducted approximately 12 days apart. Additionally, surface temperature data was obtained over the same duration from the Ranger III along the Houghton – Isle Royale transect.
However, the nutrient-rich run-off from rivers and streams is captured and held in the warmer near-shore regions of the lake. This phenomenon has a significant impact on the food-web structure in the lake. However, the thermal bar development is also a ‘big signal’ in a highly oligotrophic ecosystem like Lake Superior and therefore an important phenomenon to be modeled. http://www.aquatichabitat.ca/meteorological_conditions.shtml
These data sets provide an excellent opportunity for calibration of the hydrodynamics model.
Plans, for the next year of the project, include preparation for modeling the Keweenaw current and Ontonagon river plume in addition to particle tracking in the western basin of Lake Superior. Funding Support Provided by Great Lakes Restoration Initiative (GLRI) Grant (GL-00E00560/0) and GLRI-MTRI Acknowledgements Thanks to Dr. Nancy Auer, the Project Director, Ed Verhamme and Dr. Joe DePinto at LimnoTech Inc., for their help in setting up the EFDC model.
