Modeling the impacts of climate change on the thermal and oxygen dynamics of Lake Volta

Climatic changes influence the thermal and oxygen dynamics of a lake and thus its ecological functioning. The impacts of climatic changes on tropical lakes are so far poorly studied and the extent of the effects is therefore uncertain, most investigations describing only potential effects. In this study, we applied the one-dimensional lake ecosystem model GOTM-ERGOM to quantify the effects of climate change on thermal stratification, oxygen dynamics, and primary production in meso-oligotrophic Lake Volta. GOTM-ERGOM was calibrated and validated using two years of observed data. The validated model was used to evaluate a series of future climate change scenarios. The model simulations showed good agreement with observed water temperature, dissolved oxygen and chlorophyll-a and indicated intensified stratification and reduced oxygen levels in the productive water layers of the lake. However, the longer-lasting stratification (prolonged stability) did not translate into permanent stratification. A relatively small (1?m) upward shift of thermocline depth resulted in an 8%–12% volume loss of the oxygen-rich upper mixed layer, which may be significant for the fisheries of the lake as it diminishes the size of suitable fish habitats. Light limitation of primary production renders the lake somewhat resilient to intensive algae blooms, as traceable in both the present and in the future climate scenarios. In the long term, the ongoing climate change may affect riparian communities that depend on the lake's fisheries for their livelihood. In consequence, future lake management strategies for implementation need to account for the impacts of future climate change.