Temperature variability in lake sediments

Sediment temperatures were simulated from the sediment‐water interface down to 10 m for circular lakes with surface areas of 0.2–10 km2 and maximum lake depths of 4–24 m. The calculations were made using daily weather conditions measured over 19 years (1961–1979) at three geographic locations, representing climate conditions from north to south latitudes in the central United States. A one‐dimensional sediment temperature model coupled with a year‐round lake water temperature model (MINLAKE96) was used. The models were tested against extensive water temperature and some sediment temperature data. Lake sediment equilibrium temperatures at 10 m below the water‐sediment interface were found almost equal to the annual mean temperature of the overlaying water and hence dependent on the lake temperature regime, which in turn depends on the local climate and a lake's physical characteristics (e.g., surface area As, maximum depth HMAX, and water transparency as measured by Secchi depth). The lake geometry ratio As0.25/HMAX(m−0.5) gives a good indication whether a lake will permanently stratify in summer or not, and that makes a large difference for the sediment temperature regime. Sediment temperatures at 10 m below the littoral waters of a lake are almost equal to subsurface ground (terrestrial) temperatures, regardless of the type of lake, whereas sediment temperatures at 10 m below the deepest portion of a stratified lake have a strong linear relationship with the logarithm of the lake geometry ratio. Two generalized 10‐m sediment temperature profiles were developed, one for ice‐covered lakes and the other for year‐round open water lakes. Sediment temperatures at 10 m below the sediment‐water interface at different depths of a lake can be reconstructed from the generalized profiles using Secchi depth, surface area, maximum depth, and annual mean air temperature as input. Sediment temperature at several meters depth (e.g., 10 m) below a lake bed is a useful and necessary initial condition to predict water temperature dynamics in lakes of the temperate zone and hence other water quality parameters whose kinetics are linked to water temperature.