Variabilidade Temporal em Longo Período da Descarga Fluvial e Níveis de Água da Lagoa dos Patos, Rio Grande do Sul, Brasil

Abstract

The influence of river discharge in the marine environment is expressed in several time scales, but in long time scales it tends to control the residual pattern of behavior of these ecosystems. Studies on the dynamics of the Patos Lagoon, located in the extreme south of Brazil, are limited to considering the effect of wind and river discharge on synoptic time scales. In this sense, the objective of the study is to investigate the time variability scale of the dominant processes over the long term in river discharge and water levels in Patos Lagoon. Several time series of river discharge, water levels and Southern Oscillation Index were used to perform the study. A polynomial model based on the least squares method was used to re-construct series of water levels and statistical analysis methods were used to determine the main cycles of variability and their possible cause and effect relationship in the variables analyzed. The time series analysis suggests that on a scale of years, the river discharge accounts for over 80% of the variability in the lagoonal portion of Patos Lagoon. The river discharge in the main tributaries and the water levels in Patos lagoon are influenced on interannual scales (cycles between 3.3 and 5 years) by El Nino Southern Oscillation. The river discharge and the water levels in the region also follow a pattern of temporal variability with a decadal scale (10.8 year cycle)., which may have been associated with El Nino Southern Oscillation events, or with other oceanic and atmospheric processes of climatic kind on global scales