Climate drivers of thermal dynamics and ecosystem changes in Lake Terra Alta: a moderately deep tropical lake

Abstract Lake morphometry and local climate are key drivers of lake thermal regimes, influencing their variability across different geographic and climatic conditions. The thermal stratification and mixing dynamics of Lake Terra Alta (LTA), a moderately deep tropical lake ( A = 3.9 km 2 , Z max = 24.2 m, Z mv = 9.9 m) located in southeastern Brazil, are discussed in respect to the interannual climate variability and episodic meteorological events in three key ways: (1) droughts and reduced lake levels enhance stratification strength; (2) short-term meteorological events—such as cold fronts, South Atlantic Convergence Zone activity, storms, and heat waves—alter thermal structure; and (3) these dynamics determine the spatiotemporal distribution of dissolved oxygen and phytoplankton biomass. Daily thermal indicators and local climate variables were continuously monitored between June 2014 and May 2018 by using a meteorological station and water temperature loggers mounted on an LTA-moored platform. Monthly profiles of photosynthetically active radiation, dissolved oxygen, chlorophyll, and cyanobacteria density were recorded using a multiparameter sonde. LTA is a warm monomictic system with a relatively low theoretical water retention time of 1.7 years. During the thermally stratified season, the lake develops anoxic bottom waters below the mean depth of 9.4 m, affecting approximately 30% of the lake volume. Maximum metalimnetic chlorophyll and cyanobacteria density occur during this period. The severe 2014/15 drought resulted in a 32.9% reduction in lake volume, culminating in oxygen depletion and a massive fish kill by the end of the 2015/16 stratification season. These findings inform adaptive management and resilience of moderately deep tropical lakes under climate change.