Behavior of selected micro and trace elements and organic matter in sediments of a freshwater system in south-east Brazil

The Cima Lake (CL) is a freshwater system located in the Northern Region of Rio de Janeiro State. It has a history of agricultural and cattle raising activities. The original Atlantic forest has been deforested and replaced by pasture and sugar cane crops. The objectives of this study were to understand the vertical distribution of organic matter and heavy metals associated with lacustrine sediments and to evaluate the influence of land use on the relative contribution of organic matter sources and heavy metals to the lake sediments. For these purposes, sediment cores were collected at three stations: inlet, center and outlet of the CL. It was possible to date sediments buried over the last 150 years. The results revealed that the changes caused by human intervention in the CL watershed influenced sediment sources and composition, and led to increasing sedimentation rates over the past century. The (C/N)a ratios ranged between 5.7 and 47.4 and showed that between the 1950s and 1960s there was an alteration in the sources of organic matter to CL sediments, indicating a period marked by the expansion of sugar-cane and alcohol industries in the region and an intense deforestation in the lake watershed. The heavy metal concentrations obtained in this study were similar to those described for natural systems, in spite of the system being influenced by anthropogenic sources. The Me+/Ti ratios indicate the existence of human intervention processes in the lake, showing that the origin of metals is not only from natural processes.