Avaliação das alterações da composição da matéria orgânica particulada do Rio Negro sob diferentes cenários de mudanças climáticas

Abstract

Climate change significantly affects aquatic ecosystems by influencing the dynamics of particulate organic matter (POM) and its role in the carbon cycle. This study investigated changes in the molecular composition of POM from Rio Negro water under different simulated climate scenarios, using gas chromatography coupled with mass spectrometry (GC-MS). Water samples were incubated for one month under four conditions (control, mild, intermediate, and severe), with progressive increases in temperature and CO₂ compared to forest reference values. POM was isolated by filtration (0.7 µm), extracted with dichloromethane:methanol (2:1, v/v), concentrated, and analyzed by GC-MS. The predominant compound classes were n-alkanes and fatty acid methyl esters (FAMEs), suggesting a likely origin from microbial degradation of more complex lipid compounds. The dominance of long even-numbered n-alkanes (C₂₄–C₂₉) — an atypical profile for systems with terrestrial inputs — suggests internal recycling processes of POM mediated by microorganisms. Across all three experimental scenarios, incubation time emerged as the main factor driving molecular transformations in POM, surpassing the direct effects of the simulated climate variables. A consistent pattern of intermediate accumulation followed by decline at later stages was observed, indicating successive cycles of lipid compound release, consumption, and possible partial mineralization. Multivariate analyses (PCA and HCA) confirmed chemical separation by incubation time and revealed coherent clustering of compound classes. From an environmental perspective, the organic matter (OM) results show that even under critical conditions (RCP 8.5), no significant structural alterations could be attributed exclusively to warming or elevated CO₂ levels. These findings highlight the resilience of recalcitrant POM fractions and underscore the importance of temporal incubation processes for understanding the molecular dynamics of OM in Amazonian environments.