Modelling of summer stratification of morphologically different lakes.

The use of a one-dimensional lake temperature model was investigated using long series of meteorological input data. These data were mainly based on one station. Effects of morphology on water temperature conditions were considered over this long period. The studied lakes are from the Finnish Lake District. Concerning their dynamics, they are small with areas ranging from 257 km² to 0.14 km² with the largest depth about 80 m, but typically less than 50 m. The strength of thermal stratification varies. Verification was made using test summers: for two larger lakes longer periods could be used. Summer stratification periods could finally be resolved satisfactorily, but only after adjusting with data from each lake. For some years the vertical temperature simulations are not as successful as for others, indicating the importance of local weather differences. For lakes with a large area to depth ratio heat is absorbed freely, while when it is small heat is blocked more into the epilimnion. For very small lakes sheltering is essential. Large total volume delays cooling, when stratification prevails. Sheltering is important and also very small lakes cool slowly due to their strong stability. [ABSTRACT FROM AUTHOR]