pedro alcântara, alexandra cravo & josé jacob cima - fcma, university of algarve, campus de...
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Pedro Alcântara, Alexandra Cravo & José Jacob
CIMA - FCMA, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
Variability of nutrients & chlorophyll a in Ancão inlet
during a Spring tidal cycle in April 2009
Study Area
• Southern Portugal (36° 58’ N, 8° 2’ W to 37° 3’ N, 7° 32’ W) • ≈ 80 km2, 55 km E-W, 6 km maximum width• Shallow (average depth <2 m), semidiurnal tides, meso-tidal lagoon,(mean tidal amplitude ~2 m)• Communicate with the Atlantic Ocean through 6 inlets• Great water renewal, ≈ 80x106 m3 in neap tides to ≈ 150x106 m3 in spring tides.
Study AreaAncão Inlet• São Luis or Ancão inlet is the most western bar, artificially opened in 1997 to improve water circulation between the ocean and the lagoon. • Relatively small contribution to the water volume exchange over a tidal cycle (< 10%).
• Previous work lead to the first approach to quantify the nutrients & chlorophyll a balance through this inlet
• Main Objective• Calculate the net mass flow of nutrients and chlorophyll a
through this inlet and compare the results obtained with previous surveys conducted on 2007
Methods & Field Experiments
TrS
TrE StH
• One Survey over a complete Spring tidal cycle ~ 13 Hrs (27-04-09)
•Current Velocity Measurements with ADCP
Hourly
•Temperature, salinity, pH, dissolved oxygen in situ (YSI 6600 XL)
•Water sampling to determinate chlorophyll a and nutrient concentrations(described by Lorenzen and Grasshoff et al., 1983, respectively)
• Flow rate (Q) = Velocity x Section Area• Transport of nutrients and chlorophyll = Q x Concentration integrated over the complete tidal cycle providing the net transport.
Results CURRENT VELOCITIES
Flood > Ebb
Results
INTENSE UPPWELLING before
Survey
15-04-09 / 22-04-09 23-04-09 / 30-04-09
Chl a Satellite Images
LOWER during Survey
HOW THIS AFFECT THE RESULTS ?!?
Results
6 8 10 12 14 16 18 2070
80
90
100
110
120
130
0
1
2
3
4
HORA
% S
AT
UR
AÇ
ÃO
O2
ALT
UR
A (
m)
6 8 10 12 14 16 18 206.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
10.0
0
1
2
3
4
HORA
O2 (
mg/L
)
ALT
UR
A (
m)
6 8 10 12 14 16 18 207.0
7.2
7.4
7.6
7.8
8.0
8.2
8.4
8.6
8.8
9.0
0
1
2
3
4
HORA
pH
ALT
UR
A (
m)
6 8 10 12 14 16 18 2035.0
35.2
35.4
35.6
35.8
36.0
36.2
36.4
36.6
36.8
37.0
0
1
2
3
4
HORA
SA
LIN
IDA
DE
(‰
)
ALT
UR
A(m
)
IN SITU PHYSICAL & CHEMICHAL PARAMETERS
6 8 10 12 14 16 18 2012
13
14
15
16
17
18
0
1
2
3
4
HORA
TE
MP
ER
AT
UR
A(°
c)
ALT
UR
A (
m)
14,1 <T (°C)<17
36,24<Sal.(‰)<36,65
8,12<pH<8,35
7,29<O2(mg/L)<9,70
90<% Sat. O2<121
Results
6 8 10 12 14 16 18 200.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
1
2
3
4
HORA
SIL
ICA
TO
S (
µM
)
ALT
UR
A (
m)
6 8 10 12 14 16 18 200.0
0.1
0.2
0.3
0.4
0.5
0
1
2
3
4
HORA
FO
SFA
TO
S (
µM
)
ALT
UR
A (
m)
6 8 10 12 14 16 18 200
0.1
0.2
0.3
0.4
0.5
0
1
2
3
4
HORA
NIT
RA
TO
S +
NIT
RIT
OS (
µM
)
ALT
UR
A (
m)
NUTRIENTS
SiO44- < 2,5 µM <
ST07
NO2- + NO3
-< 0,2 µM < ST07
PO43- < 0,2 µM ~
ST07
CHLOROPHYLL a
Results
6 8 10 12 14 16 18 200
1
2
3
4
5
6
7
0
1
2
3
4
SM
HORA
Chl a
(µg/
L)
ALTU
RA (m
)6 8 10 12 14 16 18 20
70
80
90
100
110
120
130
0
1
2
3
4
HORA
% S
ATUR
AÇÃO
O2
ALTU
RA (m
)
0,1 < Chl a (µg/L) < 6,2 > ST0714:00 / 18:00 - F M S
Consistent with O2 values
ResultsST 2009
ST 2007
15-04-09 / 22-04-09 02-06-07 / 09-06-07
ST 2009 > ST 2007
Higher IMPORTATION of Chl a through inlet
LOWER NUTRIENTS conc. in ST2009
Chl a Satellite Images
ST 09
IMP(Kg) EXP(Kg)
NO2- + NO3
- 3,9
SiO44- 51
PO43- 16
Chl a 23
Results
ST 07
IMP(Kg) EXP(Kg)
36
219
0,8
2,8
TIDAL PRISM
RESIDUAL TRANSPORT
Conclusions•The results of this ST survey, during the spring season revealed this Inlet of importation of water, revealing that this is a dynamic inlet within a complex system of 6 inlets.
•Chlorophyll a concentration out of the Ria Formosa was high (max. ~6 µg/L) and higher than in ST07
•Consequently, the nutrients concentration were out and within the Ria Formosa lower than in ST07.
• Chl a, nitrate and phosphate were imported to the Ria Formosa. Silicate was the only nutrient that revealed to be exported from this system. •Nevertheless these data may change either due to dynamic alterations of this inlet or by the biological and chemical characteristics of the boundary water masses mixing associated with oceanographic processes. •To further understand this inlet a survey during a winter period of heavy rainfall is planned.