Modeling trace metals in an estuarine system under the influence of atmospheric deposition

Name: Franciane Entringer Curbani
Type: PhD thesis
Publication date: 30/09/2022

Namesort descending Role
Julio Tomás Aquije Chacaltana Advisor *

Examining board:

Namesort descending Role
Bruno Furieri Internal Examiner *
José Antônio Tosta dos Reis Internal Examiner *
Julio Tomás Aquije Chacaltana Advisor *
Levi Pompermayer Machado External Examiner *
Renato Rodrigues Neto External Examiner *

Summary: 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
(semi)metals were analyzed according to the hydrodynamic conditions and the
physicochemical characteristics of the water. 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. 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 according
to the physicochemical conditions of the water was implicitly considered through
reprofunctions for the partition coefficients. The values found of KD As-SS (55.02 –
75.46 m3
/kg) and Cr-SS (109.60 – 146.80 m3
/kg) were within the range observed in
estuarine environments, showing a negative relationship with the salinity distribution.
Critical regions were identified for the deposition of trace metals in the SEIV surface
sediment in the upper estuary, marginal areas and corresponding to mangrove
areas, in addition to the inner marine region. A predominant erosive characteristic
was observed in the middle estuarine region, in the Vitória Bay channel. 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, with a consequent increase in concentrations in the water.
Under extremely high flow conditions of the Santa Maria da Vitória River, there was
an increase in KD, accompanying the 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. In the
upper region the higher sedimentation rate of As and Cr adsorbed to suspended
sediments explained the greater influence of atmospheric input, being the region with
the highest deposition rates of suspended sediments and higher KD values. In the
inner marine region, the influence of atmospheric deposition can be associated with
the greater relationship between air-water interface area and depth, which results in
greater mass loading of As and Cr from the atmosphere to the water compared to the
outer marine region, and higher deposition rates of suspended sediments and
adsorbed (semi)metals. No potential changes were identified in the sediment quality
levels for As and Cr due to atmospheric deposition in the evaluated time scales
considering the ERL (effects range – low). The areas of greatest contribution
coincided with the preferred areas for deposition of (semi)metals in the surface
sediment identified along the SEIV. Keeping the atmospheric deposition conditions
and river loads considered in the present study, under the configurations and forcings
of the implemented models, new areas can be exposed to levels of toxicity for the
aquatic biota for As, however, it is not expected that possible changes in surface
sediment quality levels will be conditioned by atmospheric deposition in 25, 50 and
100 years.

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