Modelagem de metais traço em um sistema estuarino sob influência de deposição atmosférica

Abstract

In this thesis a hydrodynamic model and a process-based water quality model were used to study the behavior of the trace (semi)metals As and Cr in the Vitória Island Estuarine System (VIES), including the entry via atmospheric deposition. The SEIV is located in a region under the influence of atmospheric emissions, with the presence of steel and iron ore pelletizing industries, and ports that are among the busiest in the world. The metal model considered the processes of sorption of metals to suspended sediments, sedimentation and resuspension. The spatio-temporal variability of the partition coefficient KD for As and Cr between suspended sediments (SS) and water was considered through reprofunctions for the partition coefficients. The influence of atmospheric deposition on As and Cr concentrations in surface sediment was quantified on time scales of 25, 50 and 100 years, estimated from the simulation of a reference year (2010). The values found of KD As-SS (55.02 – 75.46 m3 /kg) and CrSS (109.60 – 146.80 m3 /kg) were within the range observed in estuarine environments. Critical regions were identified for the deposition of trace metals in the surface sediment in the upper estuary, marginal areas and corresponding to mangrove areas, in addition to the inner marine region. The highest bottom shear stresses occurred associated with the maximum amplitudes of the spring tide, promoting an increase in the resuspension fluxes of As and Cr from the surface sediment layer. Under extremely high flow conditions, there was an increase in KD, with an increase in suspended sediments and in the particulate fraction of (semi)metals in the water. The greatest influence of atmospheric deposition on As and Cr concentrations in the surface sediment was observed in the upper estuarine region, followed by the inner marine region. No changes were identified in the sediment quality levels for As and Cr due to atmospheric deposition in the evaluated time scales considering the Effects Range-Low (ERL). Keeping the atmospheric deposition and the settings of the implemented models, SEIV areas can be exposed to levels of toxicity for the aquatic biota for As, but not conditioned by atmospheric deposition in 25, 50 and 100 years. High levels of As in SEIV surface sediments require studies to identify sources of trace metal contamination. More research is needed correlating air pollution and water pollution, since only a few studies address this route of contamination.