Pedro Alcântara, Alexandra Cravo & José Jacob CIMA - FCMA, University of Algarve, Campus de Gambelas, 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 km 2, 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, ≈ 80x10 6 m 3 in neap tides to ≈ 150x10 6 m 3 in spring tides.

Study Area Ancão 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 ( ) 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 / / Chl a Satellite Images LOWER during Survey HOW THIS AFFECT THE RESULTS ?!?

Results IN SITU PHYSICAL & CHEMICHAL PARAMETERS 14,1 <T (°C)<17 36,24<Sal.(‰)<36,65 8,12<pH<8,35 7,29<O 2 (mg/L)<9,70 90<% Sat. O 2 <121

Results NUTRIENTS SiO 4 4- < 2,5 µM < ST07 NO NO 3 - < 0,2 µM < ST07 PO 4 3- < 0,2 µM ~ ST07

CHLOROPHYLL a Results 0,1 ST07 14:00 / 18:00 - F  M  S Consistent with O 2 values

Results ST 2009ST / / 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) NO NO 3 - 3,9 SiO PO Chl a23 Results ST 07 IMP(Kg)EXP(Kg) ,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.