EFFECT OF WAVES AND TIDES ON SUSPENDED LOAD, LOS POCITOS, BAHIA ANEGADA, BUENOS AIRES.

TONIOLO, M.A.; PERILLO, G.M.E.; CUADRADO, D.G.

SANTIAGO DE CHILE

Conferencia; 2022 Particles in the Americas Conference (PiA 2022); 2022

Particles in the Americas (PiA)

The transport and deposition of fine sediments in the coastal wetlands are often modified by the formation of flocs. The tidal flats at Los Pocitos (SW of Bahía Anegada, Buenos Aires, Argentina) are characterized by turbidity waters with high concentration of suspended particulate matter (SPM). The presence of islands limits the communication of the extensive tidal flats with the open ocean and, therefore, conditions coastal dynamics. The study includes monitoring of physical variables such as waves, tides and SPM at a EMAC station installed at the sample site. Meteorological data is gathered from another EMAC station 80 km away at the El Cóndor. The sedimentological characterization included the determination of the granulometry of the sediments of the tidal flat itself and the concentration of suspended sediment in water samples taken from the coast.The intertidal flat is characterized by very fine silty sand-sized sediments with low percentage of clay, which can form layers more than 1 cm thick. In vertical section, it is common to find filaments of cyanobacteria and EPS (extracellular polymeric substances, substances generated by microorganisms) between fine mineral grains. Likewise, the analyzes in water samples show that the SPM aggregates forming flocs with associated organic matter (OM) (with values that exceed 15% of OM present). They are frequent, abundant and vary from micro to macroflocs.The SPM curves in Los Pocitos could respond to a seasonal change (Fig. A). The lowest values were measured during spring (concentrations that rarely exceed 200 NTU with some eventual maximums), while the highest load occurs in the rest of the year (with values greater than 700 NTU). The high concentrations of SPM during the stoa would be related to the prevailing winds in the region, from the N quadrant (NNE, ENE, NNW and N). In contrast, winds from the SW, SSW, WSW and, to a lesser extent, from the ESE associated with storm events can reach speeds of over 40 km/h and generate wave heights of over 0.3 m (Fig. 1B). Despite this, they would not be related to the highest concentrations of SPM.The high density of flocs in the SPM would be associated with organic matter and EPS according to optical microscope analysis, which would precipitate in the tidal flats during stoa. This, together with the participation of microbial activity, prevents the resuspension of the sediments of the tidal flats. In this way, they constitute the main factors that explain the sedimentation of fines in high-energy environments.