Interaction between Estuarine Microphytobenthos and Physical Forcings: The Role of Atmospheric and Sedimentary Factors

PAN, JERONIMO; BOURNOD, CONSTANZA N.; CUADRADO, DIANA G.; VITALE, ALEJANDRO; PICCOLO, M.CINTIA

International Journal of Geosciences

Scientific Research Publishing Inc.

Lugar: Delaware; Año: 2013 vol. 4 p. 352 - 361

2156-8359

The goal of this study was to analyze microbial mats and biofilms from the lower supratidal area of the Bahía Blancaestuary (Argentina), and explore their relationship with sediments and other physical forcings. Thirteen monthly sedimentsamples (uppermost 10 mm) were taken and their composition and abundance in microorganisms was determinedby microscopy. Physical parameters (solar radiation and sediment temperature at −5 cm) were recorded with a frequencyof 5 minutes by a coastal environmental monitoring station. Additionally, sediment grain size and moisturecontent were determined for distinct layers in the uppermost 20 mm, and the rate of inundation of the supratidal areawas estimated from tidal gauge measurements. There were significant seasonal differences in the biomass of the microphytobenthicgroups considered (filamentous cyanobacteria and epipelic diatoms), with the former consistentlymaking up >70% of the total biomass. The relationships between microphytobenthos and sediment temperature andsolar radiation fitted to linear regressions, and consistently showed an inverse relationship between microphytobenthicabundance and either one of the physical parameters. The granulometric analysis revealed a unimodal composition ofmuddy sediments, which were vertically and spatially homogeneous; additionally, there were significant seasonal differencesin water content loss with drying conditions prevailing in the summer. Several Microbially-Induced SedimentaryStructures (MISS) were identified in the supratidal zone such as shrinkage cracks, erosional pockets, gas domes,photosynthetic domes, mat chips and sieve-like surfaces. In contrast to studies from analogous environments in theNorthern Hemisphere, we found reduced microphytobenthic biomass in summer, which were explained by increasedevaporation/desiccation rates as a consequence of increased radiation, despite frequent tidal inundation. In conclusion,the observed density shifts in the benthic microbial communities are attributable to physical forcings dependent uponseasonal variations in interplaying factors such as sediment temperature, solar radiation and tidal inundation.