There is plenty of literature about thermal startification in lakes. Just do a literature review in WOS. For pit lakes we recently pubished a book with a lot of referecnes that might help:
Geller, W., Schultze, M., Kleinmann, R. & Wolkersdorfer, C. (2013): Acidic Pit Lakes – The Legacy of Coal and Metal Surface Mines: Environmental Science and Engineering. – 525 S., 212 fig., 66 tab.; Heidelberg (Springer).
some other literature that I used in the past (and which might help you to find more):
Lorke A, Wüest A (2005) Turbulence and mixing regimes specific to lakes. In: Baumert H. Z., Simpson J., Sündermann J.. Marine Turbulance – Theories, Observations and Models, chapt. 42. Cambridge University Press, Cambridge
von Rohden C, Ilmberger J (2001) Tracer experiment with sulfur hexafluoride to quantify the vertical transport in a meromictic pit lake. Aquatic Sciences 63(4):417-431
Boehrer B (2000) Modal Response of a Deep Stratified Lake: Western Lake Constance. J Geophys Res C 105(12):28837-28845
Boehrer B, Ilmberger J, Münnich KO (2000) Vertical Structure of Currents in Western Lake Constance. J Geophys Res C 105(12):28823-28835
Ashton, P. J., Schoeman, F. R., Feb. 1983. Limnological studies on the Pretoria Salt Pan, a hypersaline maar lake: I: Morphometric, physical and chemical features. Hydrobiologia 99 (1), 61-73.
URL http://dx.doi.org/10.1007/BF00013718
Silberbauer, M. J., 1982. Phosphorus dynamics in the monimolimnion of Swartvlei. Journal of the Limnological Society of southern Africa 8 (2), 54-60.