Diana G. Cuadrado

Characterization of Microbial Mats from a Siliciclastic Tidal Flat (Bahía Blanca Estuary, Argentina)

Biofilms and microbial mats cover the tidal flats of the central zone of the Bahía Blanca estuary (Argentina), creating extensive layers. The objective of this study was to characterize the microphytobenthic communities in these biofilms and mats from sediment cores taken in March, June, September and December 2010. Microorganisms were identified and enumerated by microscopy, and their biomass (chlorophyll a, biovolume) quantified at two different stations in the lower supratidal zone, located ∼210 m apart from each other (namely S1 and S2). Additionally, the colloidal carbohydrates produced by these microbial communities were quantified, together with physical parameters such as temperature, granulometry, moisture and organic matter content of the sediment layers that comprise a typical epibenthic mat. On the other hand, changes in biomass and colloidal carbohydrate content were studied through a half-tidal cycle (7 h). There were significant seasonal differences in microphytobenthic biovolume (P < 0.001) with a considerably lower biomass in summer, but no significant differences in microalgal biovolume between stations (P = 0.454). Cyanobacterial biomass (largely composed of the filamentous Microcoleus chthonoplastes) was dominant on all dates at both stations, followed by pennate diatoms. Chlorophyll a and colloidal carbohydrate contents in sediment presented a similar pattern to that of microalgal biovolume; with a 5-fold variation in chlorophyll a for S1 between consecutive sampling events on September and December. There were significant differences between sampling dates in colloidal carbohydrates (P < 0.001) with the lowest values recorded during fall and winter; conversely there were no significant differences between stations (P = 0.324). Silt was the dominant sediment fraction at S1 while sand dominated throughout the uppermost 20 mm at S2. Chlorophyll a contents did not show significant differences throughout a half-tidal cycle, likely the product of vertical migration along the section sampled. Conversely, the content of colloidal carbohydrates varied 5-fold, showing a significant (P < 0.001) and steady increase with time of exposure to air and pointing to the rapid metabolic rates of the community. In conclusion, the microphytobenthic community of the Bahía Blanca estuary presented marked seasonality in its biological parameters and overall physiognomy, also showing elevated metabolic rates when subject to tidal fluctuations.

Geomorphologic evolution of El Toro Channel, Bahia Blanca Estuary (Argentina) prior to dredging☆

Abstract The geomorphologic evolution of the most complex reach of an area of the Bahia Blanca Estuary where dredging has been taking place was analyzed in 1987–1988 prior to the initiation of dredging. The El Toro Channel area comprises a series of channels and shoals trending NNW-SSE (ebb direction = 150°). Based on comparisons between five successive bathymetric surveys, the distribution of net erosional and depositional areas within El Toro Channel has been determined. The analysis of surface and depth-mean currents indicates that the best solution for decreasing sediment accumulation in the channel was to modify the orientation of its southern section. The selected orientation was 20° to the east of the original (new ebb direction = 130°). Approximately a year after dredging, the accumulation in this sector has, as predicted, been reduced substantially.

Tidal effects on short-term mesozooplankton distribution in small channels of a temperate-turbid estuary, Southwestern Atlantic

A variacao de curto prazo da distribuicao do mesozooplâncton e das variaveis fisico-quimicas foi examinada em dois diferentes canais do Estuario de Bahia Blanca, Argentina, durante dois ciclos de mare. As medidas fisico-quimicas e a amostragem do zooplâncton foram realizadas em dois locais fixos durante aproximadamente 22-23 horas, com intervalos de 3 horas. Bombas foram utilizadas para obter amostras de zooplâncton na superficie e no fundo e a velocidade da agua em cada estrato foi medida com o Perfilador Acustico de Corrente (ADCP). Ao todo, foram identificados 23 taxa mesozooplanctonicos pertencentes a 4 filos (Arthropoda, Annelida, Echinodermata e Chordata). Os grupos mais abundantes durante os dois ciclos de mare foram larvas de Balanus glandula, alem de Eurytemora americana e Acartia tonsa. Nos dois canais selecionados foi identificada uma variacao nas condicoes da agua e na distribuicao vertical do mesozooplâncton (DVZ) diferente daquela conhecida para o canal principal do estuario. DVZ variou durante o ciclo de mare em ambos os canais de acordo com a geomorfologia e caracteristicas da dinâmica das aguas existente em cada um deles. A variacao na abundância dos diferentes taxa durante as mares vazante e enchente poderia estar indicando a existencia de migracao vertical do mesozooplâncton em resposta a uma determinada condicao dinâmica da agua.

Study of the surface water circulation in San Blas channel (Argentina) using landsat imagery

This paper deals with the application of satellite images to study turbidity and water circulation patterns in San Blas channel during a theoretical tidal cycle. Eight Landsat TM and ETM images acquired under clear-sky conditions and representing different tidal stages were selected from a pool of Landsat images provided by the argentinean National Commission of Space Activities (CONAE) and the US Geological Survey. Standard digital image processing techniques were used to perform geometric and radiometric corrections on the visible and near-infrared bands. An image-based atmospheric correction (COST method by CHAVEZ, 1996) was applied. An ISODATA unsupervised classification was performed in order to identify different turbidity levels throughout the channel and adjacent areas. The results suggest that suspended sediment transport towards the channel mouth by ebb currents occurs along both flanks. These currents carry suspended sediment into the open sea, generating an ebb tidal delta which tends to rotate in a clockwise direction. Flood currents trigger turbidity mostly over the southern flank of the channel, generating a flood tidal delta with elongated banks extending in the direction of the tidal currents. From the elongated shape of the turbidity plumes, general tidal circulation patterns were identified.

Metals in tidal flats colonized by microbial mats within a South-American estuary (Argentina)

In this study, we measured the concentrations of metals (Cd, Cu, Pb, Ni, Cr, Zn, Hg, Mn, and Fe) and assessed the characteristics of tidal flats (grain size and organic matter content) in sediments and their overlying microbial mats fractions to evaluate the anthropogenic impact within the Bahía Blanca Estuary (BBE). Puerto Rosales (PR) and Almirante Brown (AB), located in the middle and inner zone of the estuary, respectively, were used as sampling sites. Sediments were composed mainly of silt–clay in AB, whereas first fine-grained particles were coarser in depth in PR. Regarding the concentration of metals in both fractions, we found differences between sites: There were higher concentrations of overall metals in AB relative to PR. In addition, higher concentrations of Cu were recorded in the first centimeters of AB tidal flats, whereas higher concentration of Cd were recorded in microbial mats of PR. Considering that the grain size was similar between sites, these results are consistent with the high concentration of organic matter found in AB, probably because this site is close to a former municipal dump and sewage discharges. Also, the higher Cd content found in PR site would highlight both the influence of untreated urban discharges and port anthropogenic activities. In conclusion, this study allowed identifying high values of some metals in the presence of microbial mats in the BBE, thus suggesting a possible interaction between both, at least for metals like Cu or Cd.

Coastal Environments in the Bahía Blanca Estuary, Argentina

The Bahia Blanca Estuary is a coastal system placed in a sharp transition between humid subtropical and semiarid climates, shaped by a unique combination of large interanual climatic variations and a transgressive sea level during the Holocene. In the region, the late Holocene marine transgresion resulted in low coastal landforms inherited from the former estuarine dynamics. These environments are commonly occupied by coastal ecosystems that can be roughly classified into intertidal and inland (perimarine) wetlands. Within the intertidal zone, most of the area is covered by extensive barren mudflats, and marshes are dominated by Spartina alterniflora or Sarcocornia perennis. A supralittoral zone can be defined in an intermediate position, irregularly inundated by sea water. Vegetation in this zone is sparse, with a mosaic of salt flats, halophytic steppes and shrubs forming mound-intermound complexes. The Old Marine Plain, in the inland limits of the marine transgression is not affected by tidal flooding, but an irregularly humid zone develops due to saline seepage from the uplands. These wetlands are subjected to episodic disappearance, and may get dry for several years, relying on the occurrence of rainy years during humid periods to resurge. Because of their highly dynamic nature, and the particular climatic settings of the area, these wetlands are sensitive indicators of climate change and variations in large scale circulation patterns. This chapter describes climatic patterns, geomorphological settings, and plant communities, as well as the major physical and biological interactions defining landscape structure.

Morfodinámica de un campo de dunas submarinas en una entrada de marea: San Blas, Argentina

The morphology of a submarine dune field developed in a tidal inlet that connects the Argen- tinean continental shelf with Anegada Bay (southern Buenos Aires province) was studied. The sediment circu- lation was inferred from the differential displacements of the bedforms evaluated by comparing consecutive surveys. An echosounder and a Phase Measuring Bathymetric System (PMBS) called GeoSwath were used to obtain a detailed submarine morphology. Large dunes, with heights between 4.5 and 5.0 m and from 100 to 120 m separating them, were present near the southern limit of the dune field at 24 m depth. These dunes move towards the outer part of the channel at a speed of 18 to 75 m year -1 . At the northern end of the dune field, at 21 m depth, the dunes are smaller, being 2.0 to 2.5 m in height and separated by 40 to 80 m. The smaller dunes move towards the interior of Anegada Bay at 18 to 36 m year -1 . The distribution of the water flow in the entire water column was obtained through a perpendicular profile of the channel by means of an ADCP. Maximum current speeds were 2 m s -1 , and were found during flood tide. The results obtained indicate a circulatory transport model of sedimentary sands, with the formation of ebb and flood deltas at both ends of the deep inlet throat, which lacks of unconsolidated sediments.

Aplicación de un modelo de trazadores lagrangianos en Bahía Anegada, Argentina

In this study we have applied a hydrodynamic numerical model of Lagrangian tracers to study the dispersion and subsequent settlement of particles from two different points of emission. The main objective was to define whether the particles, within the sedimentation period, could be exported out of the Anegada Bay (Argentina). We obtained the distance traveled by the particles, transported by currents induced by the tide and wind, and determined possible settlement areas. It was concluded that particles released from two different points do not leave Anegada Bay boundaries.