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.