Modeling future dissolved oxygen and temperature profiles in small temperate lake trout lakes

Abstract

Climate warming has been projected to alter the habitat ranges of cold-water fish species. To numerically model these changes, a simple dissolved oxygen (DO) sub-model has been embedded into a one-dimensional thermodynamic lake-tile model that simulates small unresolved lakes within the land surface scheme of a climate model. To account for the lack of monitoring data for most small lakes, the components of the DO budget were parameterized as functions of lake surface area and depth, a light extinction coefficient and meteorological variables prescribed by the climate model. The model predicted the temperature and DO profiles with root-mean-square error < 1.5 °C and < 3 mg l⁻¹, respectively, based on 38 years of data from two Canadian Shield lakes. For the smaller lake (~ 71 ha), simulations of future (2071–2100) lake conditions show a warming-induced reduction in the frequency of seasonal lake turnover and consequently prolonged periods of hypolimnetic hypoxia. This will reduce the end-of-summer volume weighted hypolimnetic dissolved oxygen concentration (VWHO) from ~ 6 mg l⁻¹ (1978–2005) to < 3.6 mg l⁻¹ (2071–2100), below the 7 mg l⁻¹ standard for lake trout. As a result, the height of water column with temperatures and DO concentrations suitable for lake trout will decrease from ~ 17 m to < 6 m. For the larger lake (~ 614 ha), VWHO < 5 mg l⁻¹ is predicted in the future; however, vertical mixing during turnover events and warming-induced shallowing of the thermocline depth will combine to increase the height of the suitable water column from ~ 16 m to > 18 m in the future. Hence, the lake trout populations in smaller temperate lakes may be at greater risk for earlier extirpation than in larger lakes.