EXURBAN LAKES ON THE SOUTHERN CUMBERLAND PLATEAU OF TENNESSEE - PART 1: LAKE HISTORY AND SEASONAL OVERTURN

Several small (5 to 70 acre) man-made lakes exist on the southern Cumberland Plateau in the vicinity of Sewanee, Tennessee. These lakes, which range in depth from 7 m to 15 m, were constructed by the establishment of earthen dams across first order drainages that are part of an overall dendritic drainage network developed on flat-lying, Pennsylvanian sandstones, shales, and conglomerates rich in iron and manganese oxides. The lakes were constructed beginning in the late 1950's and serve as water supply reservoirs for municipalities in the area, replacing an older system of wells and springs. These lakes have received limited attention to date in terms of changes in their chemical and temperature patterns throughout the seasons. This study investigated changes in temperature, dissolved oxygen (DO), and pH throughout the vertical extent of four lakes over the course of the past summer and fall. During the summer months these lakes developed a well-established temperature stratification with an easily recognizable epilimnion, metalimnion, and hypolimnion, with the base of the epilimnion at a depth of approximately 4 m. Coincident with this depth is a pronounced decrease in the level of DO (from 7 ppm to less than 1 ppm). The stratification by temperature was completely eradicated simultaneously in all lakes over the course of less than one week. We interpret this to be due to cooling atmospheric temperatures and concomitant turnover of the lakes. During turnover, the DO gradient in all lakes moved from a depth of 4 m to the base of the lakes and then disappeared completely over the course of subsequent weeks.