Fatores que afetam a quantidade e qualidade da matéria orgânica dissolvida em lagos naturais tropicais no médio Rio Doce

Abstract

Dissolved organic matter (DOM) is widely found in rivers and lakes and is considered the largest pool of organic matter (OM) that occurs in natural waters. It is an essential and active chemical component in terrestrial and aquatic ecosystems. It plays a vital role in the biogeochemical cycle of elements such as carbon, nitrogen and phosphorus. DOM sources in lakes can be classified according to their origin (autochthonous or allochthonous), where they have distinct optical characteristics and bioavailability. Thus, the quantity and quality of DOM affect the metabolism of aquatic ecosystems differently since it is determined by environmental factors (morphometric and climatic), which are often affected by anthropic disturbances. Despite the growing understanding of carbon cycling in temperate regions, our understanding of OM modulation and processing in tropical areas is still scarce. Thus, the objective of this work was 1) to evaluate the quantity and quality of organic matter in twelve tropical lakes inserted in different matrices (Atlantic Forest, forestry and pasture) within the lake system of the Médio Rio Doce (MG); and 2) identify the main factors responsible for the regional variation in the quantity and quality of DOM. It was possible to observe significant variation in the amount of dissolved organic carbon (DOC) and in the quality of DOM in the evaluated lakes, in which lakes inserted in the same matrix (Atlantic Forest), with similar morphometric characteristics and concentrations of DOC showed significant differences in the quality of carbon found. The DOC concentration, the aromaticity index (SUVA) and the Colored dissolved organic matter (CDOM254) of these molecules were positively influenced by parameters related to the drainage basin. On the other hand, the spectral slope (S275-295) and slope ratio (SR) were correlated with physical and chemical parameters. Considering the great importance of the entry of allochthonous organic matter in the absorption of light and, consequently, in the metabolism of tropical lakes, the understanding of its main modulators offers subsidies for the reinforcement of strategies for the conservation of aquatic environments, in addition to generating important implications for the understanding of carbon processing in tropical lakes.