Journal
Journalof
ofCoastal
CoastalResearch
Research
SI 64
pg -- pg
1619
1623
ICS2011
ICS2011 (Proceedings)
Poland
ISSN 0749-0208
Semidiurnal and spring-neap variations in the Tagus Estuary:
Application of a process-oriented hydro-biogeochemical model
N. Vaz†, M. Mateus‡ and J.M. Dias†
†CESAM, Physics
Department
University of Aveiro, Aveiro
3810-193, Portugal
[email protected],
[email protected]
‡ MARETEC, Dept. of
Mechanical Engineering
Instituto Superior Técnico,
Lisbon
1049-001, Portugal
[email protected]
ABSTRACT
Vaz, N., Mateus, M. and Dias, J.M., 2011. Semidiurnal and spring-neap variations in the Tagus Estuary:
Application of a process-oriented hydro-biogeochemical model. Journal of Coastal Research, SI 64 (Proceedings
of the 11th International Coastal Symposium), 1619 – 1623. Szczecin, Poland, ISSN 0749-0208
The main objectives of this work are the presentation of a hydro-biogeochemical model for the Tagus estuary
and the study of the interaction between tides and river discharge. Special emphasis will be given to
hydrographic, fine sediment dynamics and biogeochemical variations at two different time scales: the tidal cycle
and the fortnight cycle. The numerical model validation was performed comparing harmonic analysis results of
measured and model predicted sea surface height for 12 stations covering the whole estuary. For the M2
constituent the difference is less than 5% of the local amplitude for almost all the stations. Differences in phase
are small, with an average value of 5º. The results show strong salinity and suspended sediments gradients which
are advected up and downstream according to the tidal cycle. Moreover, the estuary is divided in three main
regions: a marine, a mixing and a freshwater influence area. The suspended sediments and chlorophyll
concentrations reveal strong fortnight time dependence near the estuary mouth. Higher concentrations of fine
sediments are found during spring tides that on neaps, which induces a decrease (increase) in the chlorophyll
concentration during spring (neap) tides. This study presents the first results of the Tagus estuary predictive
model, which are consistent with observations and with previously knowledge about the estuary. Preliminary
outcomes obtained with this high resolution numerical modeling system are very encouraging to pursuit the
development of a numerical tool suitable to deliver products that can be used both in scientific endeavors and in
estuarine management, in order to assess the ecological estuarine quality.
ADDITIONAL INDEX WORDS: Salinity, Suspended sediments, Chlorophyll, River inflow,Ttides
INTRODUCTION
Estuaries are heavy populated interface areas subject to an
enormous natural and anthropogenic stress. The knowledge of
their physical and biogeochemical characteristics and their relation
with the main driving mechanisms is a very important and actual
issue. The lack of available in-situ data covering the whole area of
an estuary limits this research, but it may be overcome by the
development and use of high-resolution numerical models.
In a first approach these models are used to study the basic
hydrodynamic features of an estuary, as performed by Fortunato et
al. (1997) for the Tagus estuary and Dias et al. (2000), Vaz et al.
(2009a) and Picado et al. (2010) in their studies in Ria de Aveiro
lagoon. Then, the coupling of robust biogeochemical models
increases the models potential and integrated studies of these
ecosystems are being performed. In the last years, this integrated
approach has been used worldwide. Baretta et al. (1995) presented
a complex marine ecosystem model called European-RegionalSeas-Ecosystem-Model (ERSEM), launching the basis for recent
ecological models. Baird et al. (2001) studied the interaction
effects of several water properties and the nutrient uptake in the
phytoplankton growth evaluating the model skill to reproduce this
processes. More recently, Lopes and Silva (2006) studied the
temporal and spatial variability of dissolved oxygen in a coastal
lagoon using a modeling approach; Saraiva et al. (2007) studied
the nutrient loads in several Portuguese estuaries and Duarte et al.
(2008) implemented an integrated watershed and biogeochemical
model for the Ria Formosa (Algarve, Portugal), analyzing the
effects induced by changes in the lagoon bathymetry, evaluating
the importance of land drainage and water exchanges for nutrient
and suspended sediment dynamics. Mateus and Neves (2008)
evaluated the light and nutrient limitations in the control of
phytoplankton production in the Tagus estuary and the results
suggest that light is the controlling factor of the ecosystem. Banas
et al. (2009) used a four-box model of planktonic nutrients
cycling, coupled to a circulation model, to evaluate how an
estuarine plume shapes the phytoplankton biomass patterns and
productivity in a regional scale. Also, Arndt et al. (2010) use a 2D
model approach in order to quantify the biogeochemical
transformations and fluxes of carbon and nutrients along the
mixing zone of the Scheldt (Belgium/Holland), revealing that the
balance between highly variable estuarine nutrient inputs and
physical constrains exert an important control on the magnitude
and succession of the ecosystem structure.
In this study, it is described the implementation and first results
of a 2D hydro and biogeochemical model for the Tagus estuary.
The main focus will be the implementation of the model, tidal
Journal of Coastal Research, Special Issue 64, 2011
1619
Semidiurnal and spring-neap variations in the Tagus estuary
Semidiurnal and spring-neap variations in the Tagus estuary
propagation and fine sediments and biogechemical variations in
the
tidal and spring-neap
cycles. and biogechemical variations in
propagation
and fine sediments
the tidal and spring-neap cycles.
STUDY SITE
The Tagus Estuary is STUDY
coastal plain
system located near Lisbon
SITE
(Portugal).
Tides
are semidiurnal
with amplitude
ranging
from
1 to
The Tagus
Estuary
is coastal plain
system located
near
Lisbon
2
4
m (over the
local
Withwith
a surface
area of
aboutfrom
320 km
(Portugal).
Tides
aredatum).
semidiurnal
amplitude
ranging
1 to
6
3
, itof is
the320
largest
and
an average
1900×10
4 m (over
the localvolume
datum). of
With
a surface m
area
about
km2
6
3
Portuguese
estuarine
systemof
(Figure
1). Intertidal
composed
m , it areas,
is the
largest
and
an average
volume
1900×10
mainly
by mudflats,
occupy (Figure
an area1).
between
20 areas,
and 40%
of the
Portuguese
estuarine system
Intertidal
composed
total
estuarine
area. occupy an area between 20 and 40% of the
mainly
by mudflats,
Theestuarine
hydrography
total
area. of the estuary is modulated by the tidal
propagation
and fluvial
discharge
the majorby tributaries
The hydrography
of the
estuary from
is modulated
the tidal
(Tagus,
Sorraia
Rivers).
interconnected
propagation
and and
fluvialTrancão
discharge
from These
the major
tributaries
forcings
appearance
sharp gradients
salinity (and
(Tagus, induces
Sorraia the
and
Trancão ofRivers).
These of
interconnected
other
variables)
inside
the estuary
withgradients
the formation
of three
forcings
induces the
appearance
of sharp
of salinity
(and
distinct
regions: ainside
marinetheregion
(lower
a mixingofregion
other variables)
estuary
withestuary),
the formation
three
(middle
estuary)a marine
and a region
region (lower
whereestuary),
the freshwater
distinct regions:
a mixing inflow
region
dominates
(upper estuary).
This is consistent
the observations
(middle estuary)
and a region
where thewith
freshwater
inflow
by
Vaz and(upper
Dias (2008)
forThis
another
Portuguese
system,
dominates
estuary).
is consistent
withestuarine
the observations
where
characterized
salinity gradients
a tidal
by Vazthey
and spatially
Dias (2008)
for anotherthePortuguese
estuarineofsystem,
channel
under
different
tidal forcing
river gradients
inflow conditions.
where they
spatially
characterized
theand
salinity
of a tidal
In
general,
thedifferent
system tidal
is well-mixed
and
hasinflow
an average
tidal
channel
under
forcing and
river
conditions.
m3. is well-mixed and has an average tidal
prism
of 600×10
In general,
the 6system
6
Theofmajor
source
m3. of freshwater is the Tagus River, with an
prism
600×10
3 -1
s . The
estuary
annual
averagesource
inflowofbetween
300-400
The major
freshwater
is themTagus
River,
withalso
an
receives
effluent
discharges,
mainly
from
several
urban,
industrial
estuary
also
annual average inflow between 300-400 m3s-1. The
and
agricultural
receives
effluentsources.
discharges, mainly from several urban, industrial
wind regime
in the region exhibits a marked seasonal
andThe
agricultural
sources.
pattern,
presenting
south
southwest
winds during
the
The wind
regime
in the
regionpredominant
exhibits a marked
seasonal
wet
seasons,
rotating
to southwest
north/northwest
during winds
the dry
season.
pattern,
presenting
south
predominant
during
the
The
seasonal rotating
variability
of meteorological
conditions
river
wet seasons,
to north/northwest
during
the dryand
season.
inflow
inducesvariability
a strongof seasonal
variability
in theand
estuary
The seasonal
meteorological
conditions
river
hydrography
and abiogeochemical
conditions
(Mateus
and estuary
Neves,
inflow induces
strong seasonal
variability
in the
2008).
hydrography and biogeochemical conditions (Mateus and Neves,
Several groups of primary producers can be found in the Tagus
2008).
ecosystem
with diatoms
being
the predominant
(Cabrita
al.,
Several groups
of primary
producers
can be found
in the et
Tagus
1999). Other
relevant
primary
in the (Cabrita
system include
ecosystem
with
diatoms
being producers
the predominant
et al.,
microphytobenthos
(Serôdio
andproducers
Catarino, in2000)
and saltinclude
marsh
1999). Other relevant
primary
the system
vegetation
(Caçador (Serôdio
et al., 1996).
microphytobenthos
and Catarino, 2000) and salt marsh
vegetation (Caçador et al., 1996).
THE TAGUS MODEL
The Tagus Estuary
predictive
model
is an implementation of
THE
TAGUS
MODEL
Mohid
(www.mohid.com)
for the
studyis area.
The model is ofa
The Tagus
Estuary predictive
model
an implementation
baroclinic
finite volume model,
coastal
estuarine
for designed
the studyfor
area.
Theand
model
is a
Mohid (www.mohid.com)
shallow water
likedesigned
Tagus estuary,
where
over
baroclinic
finiteapplications,
volume model,
for coastal
andflow
estuarine
complex water
topography,
flooding
of where
intertidal
shallow
applications,
like and
Tagusdrying
estuary,
flowareas,
over
changing topography,
stratification flooding
or mixing
all important.
complex
andconditions
drying ofareintertidal
areas,
Mohid allow
an integrated
modeling
approachareof all
physical
and
changing
stratification
or mixing
conditions
important.
biogeochemical
complete approach
descriptionofofphysical
the model’s
Mohid
allow anprocesses.
integratedAmodeling
and
physics can be found
in the A
work
by Leitão
et al. (2005).
biogeochemical
processes.
complete
description
of the model’s
Givencan
thebe
intense
mixing
of the estuary,
the model was
physics
foundvertical
in the work
by Leitão
et al. (2005).
setGiven
in a the
2D intense
mode. vertical
The numerical
grid
the whole
mixing of
theencompasses
estuary, the model
was
extension
of mode.
the Tagus
having
cells the
of 200
m
set
in a 2D
The estuary,
numerical
grid 335×212
encompasses
whole
each.
Thisofresolution
was
considered
adequate
to cells
simulate
hydro
extension
the Tagus
estuary,
having
335×212
of 200
m
and biogeochemical
processes
inside
the toestuary.
each.
This resolution was
considered
adequate
simulate Tides,
hydro
meteorological
variablesprocesses
and variable
riverthe
inflow
are theTides,
main
and
biogeochemical
inside
estuary.
forcing mechanisms
for and
the variable
circulation.
the are
open
meteorological
variables
river On
inflow
the ocean
main
boundary,mechanisms
the model input
is the
tidal forcing
fromopen
a 2Docean
tidal
forcing
for the
circulation.
On the
model (Vazthe
et al.,
2009b).
forcingfrom
(from
boundary,
model
inputMeteorological
is the tidal forcing
a the
2D Guia
tidal
meteorological
station,
http://www.mohid.com/tejomodel
(Vaz et al., 2009b).
Meteorological
forcing (from the Guia
op/atm_data.asp) and station,
river dischargehttp://www.mohid.com/tejofrom the major tributaries
meteorological
(www.snirh.pt) are
at thefrom
surface
and tributaries
landward
op/atm_data.asp)
and imposed
river discharge
the major
boundaries, respectively.
Atmosphere-water
interactions
heat
(www.snirh.pt)
are imposed
at the surface
and (e.g.
landward
fluxes, solar respectively.
radiation andAtmosphere-water
wind stress) and the
interaction(e.g.
between
boundaries,
interactions
heat
the estuary
andand
thewind
waterstress)
column
cohesive sediments
fluxes,
solarbottom
radiation
and(e.g.
the interaction
between
re-suspension
and deposition)
are column
handled (e.g.
by the
model. sediments
the
estuary bottom
and the water
cohesive
The model was
for are
2 years
(January
to December
re-suspension
and spun-up
deposition)
handled
by the2008
model.
2009)
a time
of 15fors and
a horizontal
of 5m2s-1.
The with
model
was step
spun-up
2 years
(January viscosity
2008 to December
2 -1
2 -1
for both
salt of
and
Also awith
value
of step
5 mofs 15was
s .
2009)
a time
s andadopted
a horizontal
viscosity
5mheat
2 -1
diffusion
coefficients.
for both
the hydrodynamic
s wasconditions
adopted for
salt and heat
Also a value
of 5 m Initial
model
are coefficients.
null free surface
gradient
and null
in all points.
diffusion
Initial
conditions
forvelocity
the hydrodynamic
For
thearetransport
the whole
model
null freemodel,
surfaceconstant
gradient values
and nullfor
velocity
in all estuary
points.
were
imposed.
Themodel,
spin-up
was three
months
(prior
to 2008)
in
For the
transport
constant
values
for the
whole
estuary
order
to achieve
proper was
bottom
sediment
were imposed.
Thea spin-up
three
months pattern
(prior toinside
2008)the
in
estuary.
order to achieve a proper bottom sediment pattern inside the
The ecological model (Mateus, 2006) was coupled to the
estuary.
circulation
model as
a zero(Mateus,
dimensional
water
The ecological
model
2006)
wasquality/ecological
coupled to the
model
withmodel
an Eulerian
formulation.
Thewater
model
has an explicit
circulation
as a zero
dimensional
quality/ecological
parameterization
of carbon,
nitrogen,
silica
and
model with an Eulerian
formulation.
Thephosphorus,
model has an
explicit
oxygen
cycles. Synthesis
of chlorophyll-a
is simulated,silica
allowing
parameterization
of carbon,
nitrogen, phosphorus,
and
for
a temporal
spatialofvariation
of C:Chla
ratios in producer
oxygen
cycles. and
Synthesis
chlorophyll-a
is simulated,
allowing
populations.
Light
in the of
water
column
affected
by
for a temporal
andpenetration
spatial variation
C:Chla
ratiosis in
producer
chlorophyll
and penetration
cohesive sediment
concentrations
and by
is
populations. Light
in the water
column is affected
computed
model system.
The ecological
model and
iterates
chlorophyllwithin
and thecohesive
sediment
concentrations
is
every
3600within
s and runs
for twosystem.
years. The ecological model iterates
computed
the model
Details
the runs
ecological
every
3600on
s and
for two model
years. formulation and on a prior
application
forthe
theecological
Tagus Estuary
canformulation
be found inand
Mateus
Details on
model
on a(2006)
prior
and
Mateus for
andthe
Neves
(2008).
application
Tagus
Estuary can be found in Mateus (2006)
and Mateus and Neves (2008).
RESULTS
RESULTS
Sea Surface Height
A Surface
first validation
of the numerical model was performed
Sea
Height
Figure 1. The Tagus estuary: location, station names and
bathymetry
(isolines
(in meters)
to the
local datum).
Figure 1. The
Tagus
estuary:relative
location,
station
names and
bathymetry (isolines (in meters) relative to the local datum).
through
comparison
harmonic
analysis (Pawlowicz
al., 2002)
A first
validationof of
the numerical
model wasetperformed
results
sea surfaceofheight
measurements
and modeletpredictions
throughofcomparison
harmonic
analysis (Pawlowicz
al., 2002)
for
the of
stations
depicted
in Figure
1. The data
in this
process
results
sea surface
height
measurements
andused
model
predictions
was
measured
in 1972 incovering
estuary.
for the
stations depicted
Figure 1.the
Thewhole
data used
in thisFigure
process2
depicts
the amplitude
phase difference
the two
major
was measured
in 1972and
covering
the whole for
estuary.
Figure
2
in the
Tagus
estuary. for the two major
constituents
depicts the (M
amplitude
phase
difference
2 and O1)and
the difference
For the M(M
O1) in the Tagus
estuary. between measured
constituents
2 tidal
2 andconstituent,
andFor
predicted
is less than
5% of the local
amplitude
for
tidal constituent,
the difference
between
measured
the M2 amplitudes
almost
all theamplitudes
stations. Differences
in phase
with for
an
and predicted
is less than 5%
of the are
localsmall,
amplitude
average
value
of 5º, which
represents
an average
delaywith
of 10
almost all
the stations.
Differences
in phase
are small,
an
average value of 5º, which represents an average delay of 10
Journal of Coastal Research, Special Issue 64, 2011
Journal of Coastal Research, Special Issue 64, 2011
1620
Vaz et al.
Vaz et al.
Figure 2. Comparison between amplitude and phase of the larger
(Oamplitude
in
semidiurnal
(M2) and diurnal
Figure 2. Comparison
between
and phasedetermined
of the larger
1) tidal constituents
all stations throughout
the Tagus
o – measurements
andin
*
(O1)estuary.
tidal constituents
determined
semidiurnal
(M2) and diurnal
-allmodel
predictions.
stations
throughout the Tagus estuary. o – measurements and *
- model predictions.
minutes. The exceptions are the stations located at the upstream
region
of The
the Tagus
estuary,
to the river
mouth
(stations
I, J
minutes.
exceptions
are close
the stations
located
at the
upstream
and
M).ofAt
locations,
difference
ranges
from(stations
10 to 15%
region
thethese
Tagus
estuary,the
close
to the river
mouth
I, J
of
tidallocations,
amplitude,
a degradation
the
andthe
M).local
At these
therepresenting
difference ranges
from 10 toof15%
results.
of the local tidal amplitude, representing a degradation of the
The major diurnal constituent here presented has very similar
results.
amplitude
in diurnal
all the constituent
stations ofhere
thepresented
Tagus estuary
analyzed.
The major
has very
similar
Concerning
skill in
reproducing
this constituent
amplitude inthe
all model
the stations
of the
Tagus estuary
analyzed.
differences
amplitude
are small (about
5% of the
Concerning inthe
model and
skill phase
in reproducing
this constituent
local
values).in amplitude and phase are small (about 5% of the
differences
Thevalues).
results show that the M2 amplitude is much higher than the
local
amplitude,
which
the tides
in the
estuary
are
O1The
amplitude
is much
higher
than the
results show
thatmeans
the M2that
semidiurnal
withwhich
a smallmeans
diurnalthat
inequality.
the tides in the estuary are
O
1 amplitude,
One of thewith
main
features
of the
Tagus estuary is related to the
semidiurnal
a small
diurnal
inequality.
amplification
the features
tidal wave
middle
regionisofrelated
the estuary.
One of the of
main
of in
thethe
Tagus
estuary
to the
presents
themiddle
highestregion
valuesofatthe
stations
C,
In
fact, the M2ofamplitude
amplification
the tidal wave
in the
estuary.
F, J,
andthe
K.MThis
amplification
of the tidal
amplitude
consistent
presents
highest
values atis stations
C,
In
fact,
2 amplitude
with
the results
by Fortunato
et amplitude
al. (1997) is
and
may be
F, J, and
K. Thispresented
amplification
of the tidal
consistent
related
the reflection
of the
tidal wave et
at al.
the(1997)
upstream
of
with
thetoresults
presented
by Fortunato
andregion
may be
the
estuary.
the tidalofwave
reaches
region
of the
related
to theAs
reflection
the tidal
wavetheat upstream
the upstream
region
of
estuary,
it isAsreflected
this reaches
shallowthe
region
turning
backof and
the estuary.
the tidalinwave
upstream
region
the
meets
that is in
stillthis
propagating
upstream.
Thisback
process
estuary,theit wave
is reflected
shallow region
turning
and
induces
a resonance
a period close
to twelve
in
meets the
wave that mode
is stillwith
propagating
upstream.
This hours
process
the
estuary,
as described
Oliveira
(1993).
This
effect enhances
induces
a resonance
modebywith
a period
close
to twelve
hours in
the amplitude
the tidal by
wave
at the mixing
of theenhances
estuary.
estuary, asofdescribed
Oliveira
(1993). region
This effect
general, of
thethe
results
show at
a the
fairmixing
comparison
model
theInamplitude
tidal wave
regionbetween
of the estuary.
results
and observations,
revealing
that
the modelbetween
can accurately
In general,
the results show
a fair
comparison
model
reproduce
observed tidal
propagation.
results andthe
observations,
revealing
that the model can accurately
reproduce the observed tidal propagation.
At high tide (Figures 3b and c) it is noticeable the division of
theAtestuary
in three
main 3b
regions:
marine
regions extending
from
high tide
(Figures
and c)a it
is noticeable
the division
of
the estuary
estuary inmouth
to ~10-15
kma marine
upstream
with extending
salinity values
three main
regions:
regions
from
ranging
between
36 psu,
mixing region
the estuary
mouth30toand
~10-15
kma upstream
with which
salinityincludes
values
the
central
region30
of and
the estuary,
salinities
between
10
ranging
between
36 psu, apresenting
mixing region
which
includes
and
30 psu,region
and aoffluvial
region,presenting
where thesalinities
freshwater
effect 10
is
the central
the estuary,
between
dominant.
These
considering
several
and 30 psu,
and regions
a fluvialare
region,
where characteristic
the freshwaterofeffect
is
estuarine
and the
found characteristic
are consistentofwith
the
dominant.systems,
These regions
areresults
considering
several
observations
by Vazand
andthe
Dias
(2008)
for Ria
Aveiro, revealing
estuarine systems,
results
found
are de
consistent
with the
the
model skill
reproducing
observations
byinVaz
and Dias typical
(2008) estuarine
for Ria depatterns.
Aveiro, revealing
previously
the typical
suspended
sediment
concentration
theAs
model
skill in referred,
reproducing
estuarine
patterns.
presents
similar patterns.
sourcesediment
of suspended
sediment
As previously
referred,The
themajor
suspended
concentration
in
the estuary
is patterns.
the TagusThe
river
inflow.
Theofmajor
concentrations
presents
similar
major
source
suspended
sediment
of
sediment
nearriver
the upper
estuary
(between
30 and 35
in the
estuaryareis visible
the Tagus
inflow.
The major
concentrations
-1
), where
river near
effectthe
is upper
dominant,
decreasing
downstream
mgL
of sediment
arethe
visible
estuary
(between
30 and 35
-1
). During
the low tide,
the river
toward
mouth
to 0 mgL
where
the (close
river effect
is dominant,
decreasing
downstream
mgL-1),the
effect
its influence
andthe
thelow
estuary
presents
tide, the
river
towardextend
the mouth
(close to 0downstream,
mgL-1). During
until
region of
8 km
concentrations
30 downstream,
and 35 mgL-1and
effect extend itsbetween
influence
thea estuary
presents
downstream
of between
the river mouth.
concentrations
30 and 35 mgL-1 until a region of 8 km
From low-to-high
tide,
it is visible an upstream migration of
downstream
of the river
mouth.
high
saline
waters (astide,
expected
theantide
is rising).
This water
From
low-to-high
it is since
visible
upstream
migration
of
migration
an (as
extension
of since
aboutthe
15tide
kmisupstream
during
high salinehas
waters
expected
rising). This
watera
spring
tide has
(Figures
3, b and d),
neaps
(~8-10a
migration
an extension
of being
aboutsmaller
15 kmduring
upstream
during
km,
nottide
shown).
spring
(Figures 3, b and d), being smaller during neaps (~8-10
km, not shown).
Spring-neap analysis
The study ofanalysis
the suspended sediment dynamics is very
Spring-neap
important
sinceof itsthevariation
alongsediment
the estuary
modulates
the
The study
suspended
dynamics
is very
behavior
several
(e.g. chlorophyll).
In
importantofsince
itsbiogeochemical
variation alongvariables
the estuary
modulates the
abehavior
recent paper,
Valente
and Silva (2009)
studied
turbid plume
of several
biogeochemical
variables
(e.g.the
chlorophyll).
In
of
the Tagus
estuary,
revealing
its spring-neap
modulation.
a recent
paper,
Valente
and Silva
(2009) studied
the turbid plume
4 shows
a 1 revealing
month time
of cohesive
sediments and
of Figure
the Tagus
estuary,
its series
spring-neap
modulation.
chlorophyll-a
for athe
outertime
monitoring
stations in
the Tagus
Figure 4 shows
1 month
series of cohesive
sediments
and
estuary
(Stations
andouter
E) formonitoring
April 2009,stations
when the
river
chlorophyll-a
forHthe
in Tagus
the Tagus
, in order
to capture
inflow
an average
~1502009,
m3s-1when
estuary has
(Stations
H and value
E) forofApril
the Tagus
river
3 -1
different
patterns
of
fine
sediments
near
the
estuary
s Tagus
, in order
to mouth.
capture
inflow has an average value of ~150 m
For station
E of
(farfine
from
the estuary
mouth,
the
different
patterns
sediments
near the
Tagus Figure
estuary 4b),
mouth.
-1
.
suspended
sediment
rangesmouth,
from 1Figure
to 1.54b),
mgLthe
For station
E (far concentration
from the estuary
-1
This
concentration
suspended sediments
is consistent
.
suspended
sedimentofconcentration
ranges from
1 to 1.5with
mgLthe
results
of Jouanneau
et al. (1998).
Theyis consistent
present suspended
This concentration
of suspended
sediments
with the
results of Jouanneau et al. (1998). They present suspended
Tidal cycle analysis
The cycle
Tagus analysis
estuary is a coastal plain estuary where the
Tidal
combination
and river
inflow
forcings
induces
The Tagusbetween
estuarytheis tidal
a coastal
plain
estuary
where
the
the
formationbetween
of estuarine
properties
which
combination
the tidal
and riverspatial
inflow gradients,
forcings induces
propagate
up and
according spatial
to the tidal
stage. Figure
the formation
of downstream
estuarine properties
gradients,
which
3
show theup
horizontal
patterns of
salinity and
suspended
sediments
propagate
and downstream
according
to the
tidal stage.
Figure
at
two distinct
moments
of theoftidal
cycle:
low
and highsediments
tide. The
3 show
the horizontal
patterns
salinity
and
suspended
salinity
and suspended
patterns
similar,
at two distinct
moments ofsediment
the tidal cycle:
loware
andfound
high tide.
The
revealing
a strong
spatial gradient
salinity and
suspended
sedimentthroughout
patterns the
areestuary.
found similar,
revealing a strong spatial gradient throughout the estuary.
Figure 3. .Horizontal patterns of salinity and cohesive sediments
-1
the Tagus estuary,
low and
tide cohesive
(a, c) andsediments
high tide
[mgL
Figure ]3.in.Horizontal
patterns during
of salinity
(b,
d).-1Spring
period
in April
2009.
] in thetide
Tagus
estuary,
during
low tide (a, c) and high tide
[mgL
(b, d). Spring tide period in April 2009.
Journal of Coastal Research, Special Issue 64, 2011
Journal of Coastal Research, Special Issue 64, 2011
1621
Semidiurnal and spring-neap variations in the Tagus estuary
Semidiurnal and spring-neap variations in the Tagus estuary
Figure 4. .(a) Water level at station E for April 2009; (b)
represents
evolution
of suspended
Figure 4. the
.(a)time
Water
level at
station E sediments
for April (thin
2009;black
(b)
line)
and chlorophyll
concentrations
(thick black
line) (thin
for station
represents
the time evolution
of suspended
sediments
black
E;
(c)and
represents
the same
as b) for Station
(closer
to for
the station
Tagus
line)
chlorophyll
concentrations
(thick H
black
line)
estuary
mouth). The
and
units
are
E; (c) represents
the suspended
same as b) sediment
for Station
H chlorophyll
(closer to the
Tagus
depicted
in the figure.
estuary mouth).
The suspended sediment and chlorophyll units are
depicted in the figure.
sediment concentrations of 0.8-1.0 ftu (1ftu – Formazine Turbidity
region ftu
near(1ftu
the –Tagus
estuary
mouth.
Unit
- ~1.7
mgL-1) for the
sediment
concentrations
of 0.8-1.0
Formazine
Turbidity
-1
For
station
H (closer
to region
the estuary
mouth,
the
) for the
near the
TagusFigure
estuary4c),
mouth.
Unit - ~1.7 mgL
suspended
concentration
ranges mouth,
betweenFigure
1.5 and4c),
4 mgL
For stationsediment
H (closer
to the estuary
the
1
during
spring
tides,
decreasing
to
concentrations
between
1.5
and
suspended sediment concentration ranges between 1.5 and 4 mgL1
2.2
during
neaps.
This
monitoring
station is closer
to the 1.5
estuary
during
spring
tides,
decreasing
to concentrations
between
and
mouth
and the
concentrations
are more
influenced
2.2 during
neaps.
This monitoring
station
is closerbytothe
theestuarine
estuary
discharge.
concentration are
of more
suspended
sediments
the
mouth and The
the concentrations
influenced
by theinside
estuarine
estuary
is higher
and the advection
during spring
tides isinside
enhanced
discharge.
The concentration
of suspended
sediments
the
due
to is
thehigher
large and
tidalthecurrents.
both stations
is noticeable
estuary
advectionInduring
spring tides
is enhanceda
marked
fortnight
with higher
concentrations
springa
due to the
large cycle,
tidal currents.
In both
stations isduring
noticeable
tide
and fortnight
lower during
This is concentrations
a direct consequence
of the
marked
cycle,neaps.
with higher
during spring
influence
of the during
estuarine
discharge
to athe
near-shelf.
tide and lower
neaps.
This is
direct
consequence of the
Analyzing
theestuarine
chlorophyll
concentration,
the results show that
influence
of the
discharge
to the near-shelf.
slightly
higherthe
concentrations
are computed in
(closethat
to
Analyzing
chlorophyll concentration,
thestation
resultsHshow
the
Tagus
mouth,
Figure 4c).are
Despite
this in
small
difference,
slightly
higher
concentrations
computed
station
H (closethe
to
chlorophyll
time series
present
the samethis
pattern
both stations.
the Tagus mouth,
Figure
4c). Despite
smallatdifference,
the
During
spring
tides
the chlorophyll
decreases
while
chlorophyll
time
series
present the concentration
same pattern at
both stations.
during
concentration
increases.
This is decreases
quite visible
in
During neaps
springthe
tides
the chlorophyll
concentration
while
Figure
(thick
and revealsincreases.
a spring-neap
modulation
of the
during 4c
neaps
theline)
concentration
This is
quite visible
in
chlorophyll
in theline)
region
Tagus estuary.
During spring
Figure 4c (thick
andoutside
revealsthe
a spring-neap
modulation
of the
tides
this decrease
of the
chlorophyll
concentration
is directly
chlorophyll
in the region
outside
the Tagus
estuary. During
spring
related
to the
increase
sediments
in the water.
The
tides this
decrease
of of
thesuspended
chlorophyll
concentration
is directly
available
is lowerofand
the production
is also
lower.
On The
the
related to light
the increase
suspended
sediments
in the
water.
other
hand,
during
neaps,
sediments
concentration
available
light
is lower
andthethesuspended
production
is also lower.
On the
decreases,
is more
of light
and the concentration
production is
other hand,there
during
neaps,availability
the suspended
sediments
higher.
These
patterns
consistent of
with
theand
results
presented by
decreases,
there
is moreareavailability
light
the production
is
Mateus
and Neves
where with
a higher
concentration
of
higher. These
patterns(2008),
are consistent
the results
presented by
chlorophyll
found when
the availability
of lightconcentration
is higher
Mateus andis Neves
(2008),
where a higher
of
.chlorophyll is found when the availability of light is higher
.
CONLUSIONS
In this work, the first
results of a coupled hydrodynamic and
CONLUSIONS
biogeochemical
model
the Tagus
estuary are
presented. The
In this work, the
firstofresults
of a coupled
hydrodynamic
and
model
implementation
on the Mohid
model which
biogeochemical
modelisofbased
the Tagus
estuarymarine
are presented.
The
has
been
used to studyisother
systems
in Portugal.
The
model
implementation
basedestuarine
on the Mohid
marine
model which
has been used to study other estuarine systems in Portugal. The
effort of study coupled hydro and biogeochemical features of the
Tagus
estuary
part ofhydro
an integrated
study of several
estuarineeffort of
study iscoupled
and biogeochemical
features
of the
coastal
system.is part of an integrated study of several estuarineTagus estuary
The first
results reveal that the model can reproduce the tidal
coastal
system.
propagation
along reveal
the estuary
with
small
between
The first results
that the
model
candifferences
reproduce the
tidal
predicted
seaalong
level the
height
and observations.
For almostbetween
all the
propagation
estuary
with small differences
stations
achieved
a good
of theFor
tidal
propagation.
predictedit was
sea level
height
andvalidation
observations.
almost
all the
The
exceptions
are the alocations
at the of
upstream
of the
stations
it was achieved
good validation
the tidalregion
propagation.
estuary,
and the differences
computed
mayupstream
be due toregion
an inaccurate
The exceptions
are the locations
at the
of the
numerical
bathymetry.
estuary, and
the differences computed may be due to an inaccurate
The computed
biogeochemical variables also present results
numerical
bathymetry.
which
consistent
with observations
and results
in the
The are
computed
biogeochemical
variables
also presented
present results
literature.
The cohesive
sediments spatial
patterns
reveal inhigh
which are consistent
with observations
and results
presented
the
spatial
andThe
temporal
variations.
A significant
spatialreveal
gradient
is
literature.
cohesive
sediments
spatial patterns
high
visible
in the
simulations,
with high
concentrations
the upper
spatial and
temporal
variations.
A significant
spatialingradient
is
-1
) and lower
near the estuaryinmouth
(< 5
estuary
(> the
30 mgL
visible in
simulations,
withvalues
high concentrations
the upper
-1
The
sediment
concentration
themouth
estuary
mgL
lower values
near theinside
estuary
(< is
5
estuary). (>
30cohesive
mgL-1) and
-1
determined
the freshwater
from the
river,
). The by
cohesive
sediment inflow
concentration
inside
thepresenting
estuary is
mgL
high
concentrations
during the
wet from
seasonthe(due
the high
determined
by the freshwater
inflow
river,to presenting
freshwater
discharge)during
and low
during
the high
dry
high concentrations
the concentrations
wet season (due
to the
season.
freshwater discharge) and low concentrations during the dry
The chlorophyll concentration inside the estuary is directly
season.
dependent
on the suspended
sediment
because
it
The chlorophyll
concentration
insideconcentration,
the estuary is
directly
controls
theon
light
is essential
for the chlorophyll
dependent
theavailability
suspendedwhich
sediment
concentration,
because it
growth.
spatial
distribution
of chlorophyll
inside
the estuary
controls The
the light
availability
which
is essential for
the chlorophyll
follows
patterns
found of
by chlorophyll
Mateus andinside
Nevesthe
(2008).
In
growth. the
Thesame
spatial
distribution
estuary
the
winter,
there patterns
is a clear
spatial
gradient
from low
follows
the same
found
by Mateus
andranging
Neves (2008).
In
concentrations
at isthea clear
middlespatial
and gradient
upper estuaries
higher
the winter, there
ranging to
from
low
-1
),
concentrations atatthe
(or marine)
estuary
(~3.5 mg
thelower
middle
and upper
estuaries
to ChL
higher
whilst
during the
gradient
reverses,
presenting
concentrations
at summer
the lowerthe(orspatial
marine)
estuary
(~3.5 mg
ChL-1),
lower
near the
mouth. reverses, presenting
whilst concentrations
during the summer
the estuary
spatial gradient
Tidally
driven sediment
and riverine input are
lower
concentrations
near theresuspension
estuary mouth.
important
mechanisms
theandsuspended
matter
Tidally driven
sediment affecting
resuspension
riverine input
are
concentrations
in the Tagus affecting
estuary. These
the
important mechanisms
the mechanisms
suspended affect
matter
light
availability
the estuary.
when theaffect
nutrient
concentrations
in inside
the Tagus
estuary. Thus,
Theseeven
mechanisms
the
concentration
is inside
high, the
theestuary.
light availability
is a the
keynutrient
factor
light availability
Thus, even when
(limitation)
controls
estuary
in terms
concentrationwhich
is high,
the the
light
availability
is ofa chlorophyll
key factor
concentration.
(limitation) which controls the estuary in terms of chlorophyll
In Summary the main conclusions of this study are:
concentration.
•
Thethemodel
results for sea
level
height
In Summary
main conclusions
of this
study
are: reveal small
differences
with observations.
In almost
the
•
The model results
for sea level height
revealallsmall
stations
thesewith
differences
are lower
5%all
of the
differences
observations.
In than
almost
local
both inareamplitude
stationsvariation,
these differences
lower thanand
5% phase.
of the
Therefore
an accurate
the phase.
tidal
local variation,
both invalidation
amplitude ofand
propagation
was accurate
achieved. validation of the tidal
Therefore an
•
An
amplification
of the M2 tidal constituent was
propagation
was achieved.
found
in the central
region
of theconstituent
estuary. This
was
•
An amplification
of the
M2 tidal
amplification
due to the
reflection
of the
tidal wave
found in theiscentral
region
of the
estuary.
This
in
the upstream
region
of reflection
the estuary.
Thistidal
result
is
amplification
is due
to the
of the
wave
consistent
with region
resultsof by
(1993)
in the upstream
the Oliveira
estuary. This
resultand
is
Fortunato
al. (1997).
consistent etwith
results by Oliveira (1993) and
•
The
model
predicts
Fortunato
et al.
(1997).strong salinity and suspended
sediment
spatial
gradients
the
•
The modelconcentration
predicts strong
salinity
and inside
suspended
estuary,
are advected
backgradients
and forth inside
according
sedimentwhich
concentration
spatial
the
to
the tidal
stage.
estuary,
which
are advected back and forth according
•
Due
its length,
to thetotidal
stage. the Tagus estuary may be divided in
three
and the
very
well estuary
markedmay
regions:
a lower
•
Due todistinct
its length,
Tagus
be divided
in
and
estuary;
a mixing
located
in theacentral
threesaline
distinct
and very
well area
marked
regions:
lower
area
of theestuary;
estuary aand
an upper
by
and saline
mixing
area region
locateddominated
in the central
the
inflow
the Tagus
River.
areafreshwater
of the estuary
andfrom
an upper
region
dominated by
•
The
results forinflow
the stations
mouth of the
the freshwater
from thenear
TagustheRiver.
estuary
showfora the
strong
fortnight
•
The results
stations
nearmodulation:
the mouth during
of the
spring
suspended
sediment
concentration
estuary tides,
show the
a strong
fortnight
modulation:
during
increases,
to a decrease
the light
spring tides,leading
the suspended
sediment of
concentration
increases, leading to a decrease of the light
Journal of Coastal Research, Special Issue 64, 2011
Journal of Coastal Research, Special Issue 64, 2011
1622
Vaz et al.
Vaz et al.
availability and consequently to a decrease of the
chlorophyll
concentrations.
During
neapsof the
availability and
consequently to
a decrease
suspended
concentration
decreases
leading
chlorophyllsediment
concentrations.
During
neaps
the
to
the increase
of the chlorophyll
concentration.
These
suspended
sediment
concentration
decreases leading
results
are consistent
with the results
presented
by
to the increase
of the chlorophyll
concentration.
These
Valente
and consistent
Silva (2009).
results are
with the results presented by
As previously
the preliminary results of this
Valente andreferred,
Silva (2009).
coupled
hydro referred,
and biogeochemical
As previously
the preliminarymodel
resultsareof very
this
encouraging.
Thisand
model
implementation
will allow
the
coupled hydro
biogeochemical
model
are very
development
several
which can
used the
by
encouraging. of
This
modelproducts,
implementation
willbeallow
scientists
andofmanagers
to increase
the can
knowledge
on
development
several products,
which
be used by
estuarine
processes,
contributing
to the
a more
efficient
scientists and
managers
to increase
knowledge
on
management
of the complex
and sensible
inside
estuarine processes,
contributing
to a ecosystem
more efficient
the
Tagus estuary.
management
of the complex and sensible ecosystem inside
the Tagus estuary.
LITERATURE CITED
Arndt, S.; Lacroix,LITERATURE
G.; Gypens, N. ; Regnier,
P. And Lancelot, C.,
CITED
2010.
Nutrient G.;
dynamics
and; Regnier,
phytoplankton
development
Arndt,
S.; Lacroix,
Gypens, N.
P. And Lancelot,
C.,
along
estuary-coastal
A model
study.
2010. an
Nutrient
dynamics zone
and continuum:
phytoplankton
development
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Marine zone
Systems,
84, A 49-65.
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T.D.;
Hickey,
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E. (2009),
biophysical
model study,
Geophys.
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C00B06,
growth and grazing
in the J.
Columbia
River
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Baretta,
J.W.; Ebenhoh, W. and Ruardij, P., 1995. The Europeandoi:10.1029/2008JC004993.
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Baretta,
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M.T.; Catarino, F. and Slawyk, G., 1999. Interactions of
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controlling
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Catarino, and
F. and
Slawyk, G.,
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Interactions
of
planktonic
nitrogen utilization
in thenitrogen
Tagus estuary.
Aquatic
light, temperature
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AKNOWLEDGMENTS
This paper wasAKNOWLEDGMENTS
partially supported by the Portuguese Science
Foundation
through
thesupported
research
projects
DyEPlume
This paper was
partially
by the
Portuguese
Science
((PTDC/MAR/107939/2008),
AdaptaRia
Foundation through the research
projects (PTDCAACDyEPlume
CLI/100953/2008)
and ECOSAMAdaptaRia
(ECOSAM (PTDC/AAC((PTDC/MAR/107939/2008),
(PTDCAACCLI/104085/2008))
co-funded
by COMPETE/QREN/UE.
The
CLI/100953/2008) and
ECOSAM
(ECOSAM (PTDC/AACfirst
author of this work
is supported
by the Portuguese Science
CLI/104085/2008))
co-funded
by COMPETE/QREN/UE.
The
Foundation
Ciência2008.
first author program
of this work
is supported by the Portuguese Science
Foundation program Ciência2008.
Journal of Coastal Research, Special Issue 64, 2011
Journal of Coastal Research, Special Issue 64, 2011
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