Author(s): Charlotta Borell Lovstedt
Linked Author(s):
Keywords: Natural convection; Differential heating; Reed belt; Phragmites australis
Abstract: Differential heating caused by shading from vegetation will induce a current between the open water and the reed belt in lakes. Temperature difference as a consequence of shading by reed vegetation (Phragmites australis) measured in a lake in southern Sweden is presented here. The temperature was measured in plastic tubes so not to be affected by the current, from the beginning of May to the end of October 2006. The temperature difference was considerably higher in the plastic tubes than what was measured in an earlier experiment without tubes. The average surface temperature difference 10: 00 h-17: 00 h on sunny days during the period July-September was on average 1. 15oC and as maximum 2. 53oC. The highest 30-minute value for the temperature difference was 4. 3oC. The variation in daily temperature difference during the season was correlated to the development of the vegetation and the daily average in solar radiation. For temperature differences of 0. 5-4oC the velocity scale of the induced surface current was calculated to 1. 9-5. 2 cm s-1, which is comparable to a pre-study at the site which showed that the surface current during sunny days with low wind speeds was 1. 5-2. 8 cm s-1 directed towards to reed stand. The temperature gradients are large enough to induce a current that is of importance for the exchange between the reed belt and the open water.
Year: 2007