Heronblu,
The Ekman effect doesn't occur in small private ponds or small, shallow lakes. Therefore, it isn't the cause of 'turnover.' A turnover in a pond or lake is normally stimulated by temperature changes.
In some manmade public lakes, rivers and even the Great Lakes as well as some of the bigger private waters wind currents create what's called the Langmuir effect. Look next time you drive across a bridge over water. You will likely see long, parallel streaks of floating stuff or bubbles. Continual blowing of a wind across gentle waters causes formation of cells of rotating water that parallel the surface. Picture two empty paper towel cores suspended, rolling opposite ways, side by side. Those circular currents cause upwelling from deeper waters over a long distance. While it most likely won't destratify water, it can sure send suspended 'stuff' to the surface. Hence, the bubbles, foam and floating debris. That's where the term 'flotsam' comes from.
At the same time, those two bands of converging water create downwelling, pushing fresh aerated water down. Since this 'stuff' does not sink with downward bound water, it collects to form a streak, which is what you see on the surface.
The Languir currents rarely dip below 20 feet. Below, water remains fairly still. I have seen Langmuir currents form within minutes, but often they last several hours, then dissipate. Circulation can form quite quickly, and can last from several minutes to several hours.
