Temperature, heat, and mixing in Lake Valencia, Venezuela1

Abstract

Water temperature profiles, weather data, and lake level data spanning a 2‐year period for Lake Valencia, Venezuela (10°N, 67°W), are used in an analysis of thermal regime, mixing, and heat flux. The lake, which has an area of 350 km2 and mean depth of 19 m, is warm monomictic; it becomes isothermal annually near the end of November, at the onset of the dry season. The water column during stratification consists of an upper mixed layer, which averages 13 m but varies greatly in thickness, followed by alternating thick layers of positive and negligible density gradients. The number of layers changes through time. Vertical eddy diffusivities during stratification vary from 0.23 cm2·s−1 at 20 m to 0.09 at 35 m. The mean annual heat budget is 5,308 cal · cm−2. Evaporative heat loss and net radiation flux are the two largest heat budget elements; net back radiation and sensible heat loss are important secondary terms. Seasonality is principally traceable to heat budget terms influenced by minimum air temperature, whereas week‐to‐week variation is influenced by other terms as well. Maximum stability of the water column is about 350 g‐cm · cm−2 with little variation between years. Work of the wind in distributing heat is 2,630 g‐cm·cm−2 for 1977 and 3,156 in 1978. Stability responds in a significant way to weather changes, even during stratification.