Changes in the stratification and mixing patterns of Lake Bosumtwi due to climate warming

Historically, regular mixing occurred predictably in Lake Bosumtwi in August. However, recent reports indicate a shift towards prolonged stratification, reduced seasonal mixing depth, and a decline in fish productivity, consistent with the effects of climate warming. This study aimed to investigate the perceived changes in the mixing and stratification regime by comparing historical (2004-2006) and current data to determine the magnitude of climate warming on the lake’s hydrodynamic properties. From 2018 to 2020, daily measurements of meteorological variables, including temperature, wind speed, and rainfall within the crater, were recorded at an onshore weather station. Monthly data on water column temperature, dissolved oxygen, and electrical conductivity were collected, and Schmidt stability was calculated. Time series analyses suggest alterations in the stratification and mixing patterns of the lake induced by air temperature and wind speed forcing. The air temperature increased from 26.56 °C (SD = 3.13) to 27.28 °C (SD = 3.32) resulting in a 0.30 °C rise in the water column, greater thermal stability and a decline in dissolved oxygen concentration with depth. There appears to be a notable shift in the timing and intensity of the mixing period, transitioning from August to September, attributed to diminished convective cooling processes. Evidence indicates a transition from a holomictic state to meromictic. This transformation in the lake’s hydrodynamics will affect nutrient renewal rates and primary productivity, with implications for water quality, fisheries, ecotourism, and livelihood activities vital to the lake communities.