Efeitos antrópicos em ecossistemas aquáticos: uma abordagem sob o ponto de vista da estequiometria ecológica de séston e bactérias

Abstract

Ecological stoichiometry provides a framework for understanding how the balance among carbon (C), nitrogen (N), and phosphorus (P) regulates resource quality, microbial metabolism, and nutrient cycling in aquatic ecosystems. In tropical environments subjected to anthropogenic pressures, changes in the relative availability of these elements can modify organic matter processing and the coupling among dissolved, bacterial, and particulate compartments. This thesis investigated how different human impacts affect C:N:P stoichiometry and microbial responses in tropical aquatic ecosystems. The thesis comprises a mechanistic synthesis and four articleformat chapters. Chapter 1 used bibliometric analysis to identify the main impact vectors and emerging themes in the literature, with emphasis on rivers, emerging pollutants, and microplastics. Chapter 2 showed that, in the Rio Doce basin, hydrological seasonality accelerates labile carbon turnover, whereas refractory carbon remains more persistent; the stability of C:N contrasted with the variability of C:P and N:P, reinforcing the role of P in the biogeochemical response. Chapter 3 demonstrated that, in earthen aquaculture ponds, stoichiometric coupling was more evident for N:P than for C:N, indicating stronger effects along phosphorus-related axes. Chapter 4 experimentally showed that P availability favors microbial attenuation of caffeine, a compound associated with domestic effluents.Overall, the results show that anthropogenic pressures alter aquatic ecosystems not only through the input of pollutants or nutrients, but also through the reorganization of stoichiometric relationships that support microbial metabolism and carbon cycling. Hydrology regulates the supply and processing of organic matter, while phosphorus emerges as a key element linking pools and shaping microbial responses to human disturbances.