Heating and Cooling of a Shallow Bay in Eau Galle Reservoir: Field Measurements and Interpretations Part 2 (1989)

Abstract

The distributions of nutrients in lakes and reservoirs effect water quality. Movement of water within these water bodies is the main mechanism by which nutrient transport occurs. The process of water movement within a lake or reservoir is a consequence of natural forces. These forces depend on the effects of rain, wind, solar radiation, surface cooling, ground water intrusion, photosynthetic activity, gravity, tidal effects, and the Coriolis force. This study concentrates on the effects of the diurnal heating and cooling cycle as the primary factor which causes water movement between the littoral and profundal waters in lakes and reservoirs. It has been shown that heating and cooling of water on a littoral slope induces a horizontal temperature gradient and that the density of water associated with this temperature gradient induces horizontal and vertical exchange of water along the littoral slope and adjacent profundal waters (Stefan,Horsch, and Barko, 1989). The dependence of water movement and consequent nutrient transport on the water temperature, during the diurnal heating and cooling cycle, is investigated through analysis of the time dependent temperature profiles within a shallow heavily vegetated bay and adjacent profundal waters. The effect of wind on these temperature profiles is also investigated. The data was collected in a protected bay of a flood detention basin in western Wisconsin. In this progress report some of the analyzed data is given a qualitative interpretation. The quantitative analysis, which is currently being performed, will be the subject of a future report. This study is based on temperature measurements taken with 38 temperature probes, located at six stations, in the littoral and adjacent profundal waters of Eau Galle Reservoir at 30 minute intervals during the period of May 15 to October 13, 1989. Wind speed and direction, air temperature, solar radiation, and reservoir pool elevation were also measured. This data is presented in time series plots and the interrelationship of some parameters is explored. Contour plots of the spatial distribution of temperatures within the bay transect are also presented during episodes of heating and cooling, and during a windy period to illustrate the time and spatial dependence of the water temperatures during these events. The data presented in this report were collected by Dr. William F. James and his auxiliary staff under direction by Dr. John W. Barko. The data were made available in diskettes, reviewed and plotted by the first author of this report with guidance provided by the second author. An earlier report (No. 286) dealt in a very similar fashion with the data collected in 1988 and has been back labeled Part 1 (1988). This report deals with data collected in 1989 and is, therefore, labelled Part 2 (1989).