Uso de sensores de alta frequência para estimativas contínuas de metabolismo e monitoramento em lagos tropicais

Abstract

Abstract: With technological advances, equipment for remote monitoring of environments, able to collect and store high-frequency data, have become broad spread. This new technology offers greater detail on physical, chemical and biological properties of the ecosystem, providing refinement to the study scales and robustness to data. Although tropical aquatic ecosystems are very abundant on a global scale and have unique peculiarities, studies with continuous monitoring of O2 in these ecosystems are scarce. Therefore, this PhD thesis aims to investigate the potential of environmental monitoring using high-frequency automated sensors to study metabolism and thermal structure dynamics of two tropical lakes, Carioca and Dom Helvécio (DH), located in Parque Estadual do Rio Doce, Minas Gerais, Brazil. Data from continuous monitoring buoys installed in these two lakes from May 2011 to December 2012 were used to compare the thermal structure and metabolism of these environments. The performance of seven equations used to estimate the metabolic rates from the variation of dissolved oxygen (DO) was evaluated and the models that considered photoinhibition for calculating gross primary production showed the best performance according to the Akaike Information Criterion (AIC). The two years studied showed a large discrepancy in relation to rainfall. In 2011, precipitation was approximately 5 times higher than in 2012 and the air temperature was on average 1.2°C lower. An increase in water temperature was noticed even in deeper layers and was followed by a decrease in the depth of the thermocline (2011 14.9 m; 2012 to 11.1 m , mean May-December) and a shorter full-mixing period (2011 - 89 days; 2012 - 51 days) in the deeper largest clear and with lower concentrations of colored dissolved organic matter lake, DH. Gross primary production (GPP) and respiration (R) rates were 2-fold higher during the fully-mixed winter periods compared to the summer periods. Seasonal changes and short-term variability in GPP and R were negatively linked to water column stability (GPP r = -0.82; p < 0.001; R r = -0.80; p < 0.001). Periods with high stability and warm waters reduced mixing and internal inputs of nutrient from hypolimnetic waters and these conditions occurred during periods with high mean light exposure in the upper mixed layer with clearer waters. Primary production was accordingly suppressed in both lakes during summer due to a combination of nutrient depletion and photoinhibition. GPP rates during the drier and warmer year (2012) were lower compared with the same period of the earlier year (2011), Carioca Lake was about 40% lower and DH about 15%. This indicates ecosystem responses in carbon cycling of tropical lakes to the ongoing regional climate changes. Additionally, the greater sensitivity of DH Lake highlights the importance of considering the morphometry, transparency and concentration of dissolved organic carbon to understand the effects of climate change on aquatic ecosystems.