Abstract:
Neste estudo das águas estuarinas da Lagoa dos Patos (ELP), especial ênfase é dada
na caracterização das propriedades ópticas e suas relações com constituintes opticamente
ativos. Para tanto, foram coletados dados físicos (salinidade, temperatura e velocidade da
corrente) e ópticos (absorção, atenuação, retroespalhamento, fluorescência, radiância e
irradiância) em conjunto com amostra das águas de superfície para determinação das
concentrações do material total em suspensão (TSM), material orgânico dissolvido colorido
(CDOM) e clorofila-a (CHLa) em 10 estações distribuídas ao longo do canal do ELP,em 7
cruzeiros realizados entre fevereiro e outubro de 2012. o período amostrado foi
caracterizado por baixa descarga de água doce com relativa alta carga de TSM proveniente
da re-suspensão do fundo, especialmente durante os cruzeiros de verão-outono. O TSM,
composto principalmente por minerais ou partículas inorgânicas controlou a variabilidade
das propriedades ópticas em quase todo perido amostrado. A concentração de TSM foi mais
variável (3.75 – 68.00 mg.L-1
, C.V. = 68.8%) que CDOM (9.74 – 41.41 ppb QSDE, C.V. =
31.4%) e CHLa (0.82 – 4.57 mg.m-3
, C.V. = 46.1%). TSM e CDOM mostrou correlação com a
salinidade (r=0.73 and r=-0.58, N=32, p<0.05) que o CDOM teve origem de águas fluvial, e
TSM foi maior na entrada do estuário devido à re-suspensão do material fundo. Os
espectros de IOPs e reflectância do sensoriamento remoto (Rrs) foram tipicamente Caso II
assinatura, com predominância de águas túrbidas e ricas em CDOM. Não houve diferença
estatística em propriedades ópticas foram encontrados dentro de zonas estuarinas ou
estações do ano. Análise de agrupamento hierárquico mostrou espectros de Rrs distintos
para baixo e moderado níveis de descarga de água doce, mas sem evidência clara de
coexistência de diferentes tipos de água em EPL. O TSM mostrou boa correlação com
VI
coeficientes de retroespalhamento do particulado, a 600 e 715 nm, e com coeficiente de
absorção do particulado e dissolvido em 660nm. CDOM se correlacionou melhor com a
diferença de coeficientes de absorção do particulado e dissolvido a 412 e 440 nm (r = 0,72,
N = 28, p <0,05). A influência das IOPs e constituintes opticamente ativos sobre a
variabilidade da Rrs(λ) foi avaliada por análise de EOF. Os resultados mostraram que o
primeiro modo de EOF responsável por quase toda a variabilidade dos dados (92,4%),
enquanto o segundo e terceiro modos explicam 4,7% e 2,3%, respectivamente. Os fatores
de amplitude do primeiro modo de EOF foram correlacionados com o TSM (r = 0,39, n = 32,
p <0,05) e com todas as propriedades ópticas inerentes medidos.
The Patos Lagoon, the world’s largest choked lagoon, has a very dynamic estuary in
which circulation, forced by freshwater discharge and local and remote wind, regulates the
spatial and temporal distribution of physical and biogeochemical properties in the estuary.
In this work, we present a baseline study on the variability of inherent (IOP) and apparent
optical properties (AOP) in the Patos Lagoon Estuary (PLE) with emphasis on their
relationships with optically active water constituents. The dataset consists of physical
(salinity, temperature and current velocity), optical (absorption, attenuation, backscattering,
fluorescence, and remote sensing reflectance) and biogeochemical (total suspended matter
(TSM), chlorophyll-a concentration (CHL), and colored dissolved organic matter (CDOM)
properties measured at 10 fixed stations during 7 cruises conducted between February and
October 2012. The sampling period was characterized by low river discharge but with
relatively high load of TSM. associated with bottom resuspension in the estuary entrance,
especially during the summer-autumn period. The TSM, mainly composed by minerals or
inorganic particles, controlled the variability of optical properties in almost the entire
sampling period. The total TSM was more variable (3.75 – 68.00 mg.L-1
, C.V. = 68.8%) than
CDOM (9.74 – 41.41 ppb QSDE, C.V. = 31.4%) and CHLa (0.82 – 4.57 mg.m-3
, C.V. = 46.1%).
TSM and CDOM were correlated with salinity (r=0.73 and r=-0.58, N=32, p<0.05) indicating
that CDOM originated from riverine water, and TSM was higher at the entrance of the
estuary due to bottom resuspension of material. The IOPs and remote sensing reflectance
(Rrs) spectra were typically of Case 2 signature, with dominance of turbid and CDOMenriched waters. No statistical differences in optical properties were found within estuarine
zones or seasons in this work. Hierarchical clustering analysis has shown distinct Rrs for low
to moderate freshwater discharge, but with no clear evidence of coexistence of different
water types in PLE. The TSM correlated well with backscattering coefficients, at 600 and 715
nm, and with particulate absorption coefficient at 660nm. CDOM correlates better with the
difference in absorption coefficients at 412 and 440 nm (r= 0.72, N= 28, p<0.05). The
influence of IOPs and optical constituents on the variability of Rrs(λ) was assessed by EOF
analysis. The results showed that the first EOF mode accounted for almost all data variability
(92.4%), while the second and third modes explained 4.7% and 2.3%, respectively. The
45
amplitude factors of first EOF mode were correlated with TSM (r= 0.39, N=32, p<0.05) and
with all the measured inherent optical properties
The Patos Lagoon, the world’s largest choked lagoon, has a very dynamic estuary in
which circulation, forced by freshwater discharge and local and remote wind, regulates the
spatial and temporal distribution of physical and biogeochemical properties in the estuary.
In this work, we present a baseline study on the variability of inherent (IOP) and apparent
optical properties (AOP) in the Patos Lagoon Estuary (PLE) with emphasis on their
relationships with optically active water constituents. The dataset consists of physical
(salinity, temperature and current velocity), optical (absorption, attenuation, backscattering,
fluorescence, and remote sensing reflectance) and biogeochemical (total suspended matter
(TSM), chlorophyll-a concentration (CHL), and colored dissolved organic matter (CDOM)
properties measured at 10 fixed stations during 7 cruises conducted between February and
October 2012. The sampling period was characterized by low river discharge but with
relatively high load of TSM. associated with bottom resuspension in the estuary entrance,
especially during the summer-autumn period. The TSM, mainly composed by minerals or
inorganic particles, controlled the variability of optical properties in almost the entire
sampling period. The total TSM was more variable (3.75 – 68.00 mg.L-1
, C.V. = 68.8%) than
CDOM (9.74 – 41.41 ppb QSDE, C.V. = 31.4%) and CHLa (0.82 – 4.57 mg.m-3
, C.V. = 46.1%).
TSM and CDOM were correlated with salinity (r=0.73 and r=-0.58, N=32, p<0.05) indicating
that CDOM originated from riverine water, and TSM was higher at the entrance of the
estuary due to bottom resuspension of material. The IOPs and remote sensing reflectance
(Rrs) spectra were typically of Case 2 signature, with dominance of turbid and CDOMenriched waters. No statistical differences in optical properties were found within estuarine
zones or seasons in this work. Hierarchical clustering analysis has shown distinct Rrs for low
to moderate freshwater discharge, but with no clear evidence of coexistence of different
water types in PLE. The TSM correlated well with backscattering coefficients, at 600 and 715
nm, and with particulate absorption coefficient at 660nm. CDOM correlates better with the
difference in absorption coefficients at 412 and 440 nm (r= 0.72, N= 28, p<0.05). The
influence of IOPs and optical constituents on the variability of Rrs(λ) was assessed by EOF
analysis. The results showed that the first EOF mode accounted for almost all data variability
(92.4%), while the second and third modes explained 4.7% and 2.3%, respectively. The
45
amplitude factors of first EOF mode were correlated with TSM (r= 0.39, N=32, p<0.05) and
with all the measured inherent optical properties.
