Metabolismo de lagos tropicais: efeito das alterações climáticas sazonais, morfometria dos lagos e característica de suas bacias

Abstract

This thesis aimed to study the dynamics of metabolic rates and the main drivers in 12 lakes of the middle Rio Doce (Minas Gerais, Brazil) as well as to assess the effect of climate change and morphometry. Samples were taken in 3 periods, a hot and rainy summer and a dry winter with lower temperatures (mixing period) during 2012 and another hot summer, but dry in 2013. The reduced precipitation altered the structure of lakes, reducing their volumes, and mixing layers stability, resulting in an increase in metabolic rates. These results differ from studies in temperate lakes in which the reduction in rainfall is related to increase of light availability, favoring GPP. The quality optical metrics of DOC indicated that, during drought periods, the DOC is from autochthonous and allocthonous sources, with lower molecular weight and more labile. The GPP and ecosystems respiration in lakes mixing layers were better explained by spectral slope (275-295nm), DOC concentration and light availability, indicating that photoinhibition is a striking process in these clear lakes. Indeed, the transition from a hot and rainy condition to a hot and dry one changed the composition of CDOM, from complex molecules of terrestrial origin to labile molecules from autotrophic origin. These relationships of metabolic rates and CDOM with climate change were influenced by drainage rates of the lakes. Lakes with higher drainage rates had higher metabolic rates due to higher nutrients and CDOM concentrations in epilimnion and lower light availability.