Morphometry and trophic state modify the thermal response of lakes to meteorological forcing

Within two years of contrasting temperature dynamics, 2008 and 2009, we studied the thermal and optical regime of two adjacent stratified lakes in Lombardy lake area in Italy, the oligotrophic Lake Monate (2.5 km2, max. depth 34 m) and the eutrophic Lake Varese (14.8 km2, 26 m). After the cold winter 2008-2009, a heat wave starting in May turned the whole year 2009 the second hottest after 2003. We hypothesized that (i) the summer heat wave in 2009 would increase the thermal stability of both lakes compared to summer 2008 and (ii) the differences in size and trophic state would cause systematic differences in heat distribution within the lakes¿ water columns. The particular sequence of meteorological events - the cool winter followed by a hot summer in 2009, resulted in extreme vertical temperature gradients and unusually high thermal stability of both lakes. All calculated thermal parameters, the heat content (Tt), volume-weighted mean temperature (T), Schmidt thermal stability (S), and Birgean work (B), showed the highest values in 2009 while also the values for 2008 exceeded considerably those published for these lakes in the past. Due to large wind exposed surface, wind mixing was supposedly the dominating mechanism of heat transfer in the shallower Lake Varese where due to low water transparency large amount of solar energy became trapped in the top layers increasing the contrast with bottom layers ¿ a phenomenon that is generally typical to deep lakes. Contrary, in Lake Monate, which is deeper and more transparent than Lake Varese, solar irradiance that penetrated up to the metalimnion contributed considerably to the vertical energy transfer and gave to the lake some features typical to rather shallow lakes.

NOGES Peeter;  NOGES Tiina;  GHIANI Michela;  PARACCHINI Bruno;  PINTO GRANDE Joaquin;  SENA Fabrizio; 

2011-11-30

SPRINGER

JRC59406

0018-8158,   

http://link.springer.com/article/10.1007%2Fs10750-011-0691-7,    https://publications.jrc.ec.europa.eu/repository/handle/JRC59406,   

10.1007/s10750-011-0691-7,