A semi-mechanistic seasonal temperature-profile model (STM) for the period of stratification in dimictic lakes

Abstract

A semi-mechanistic seasonal temperature-profile model (STM) for stratified lakes was successfully tested with six Ontario data sets. The STM has eight parameters: the days of year for the start and end of stratification and the midsummer surface temperature peak ([Formula: see text]); the temperature at the onset and end of stratification and [Formula: see text]; the seasonal development of the thermocline depth (two parameters); and the steepness of the depth transition from epilimnion to hypolimnion. The STM was fitted using nonlinear least squares with R2 ranging from 0.91 to 0.99 and root mean square errors of 0.80 to 1.42 °C. Residuals were evenly distributed with respect to date and depth with 69.4% to 95.9% ± 1.0 °C. On average, observed-estimated temperature differences range from –0.24 to –0.03 °C and +0.16 to +0.37 °C for estimated temperatures of 5 and 25 °C, respectively. Simulations with daily data sets showed the STM fit was insensitive to reductions in the length of sampling duration and sampling frequency. Several STM parameters were well-estimated by published equations based on morphometric, climatic, and location variables.