Abstract

ANGELETTI, Sabrina; LESCANO, Leticia  and  CERVELLINI, Patricia. Biosedimentological and mineralogical characterization of two intertidal areas of Bahia blanca estuary. Geoacta [online]. 2014, vol.39, n.2, pp.54-67. ISSN 1852-7744.

In this paper the biosedimentation and mineralogy of intertidal sediments of two sites of the Bahía Blanca estuary, and its relation to plant species and population dynamics of Neohelice granulata was analyzed. Two transects perpendicular to the subtidal were placed; A transect in Puerto Cuatreros and B in Villa del Mar. Sampling was conducted from March to June 2013. Two stations at each transect were selected, where surface sediments (control) and sediments removed by crabs were analyzed through environmental, textural and mineralogical studies. Density of burrows, vegetation cover and environmental data were also recorded. For the granulometric and mineralogical studies, loose grain method under the microscope and X-ray diffraction were done using standardized laboratory methods. The XRD results revealed that in both study sites, intertidal sediments were represented by minerals like quartz, feldspar and halite, and in lesser proportions were found clays such as illite and montmorillonite. The clay fraction prevailed in intertidal sediments of Puerto Cuatreros (50-45%) over samples of Villa del Mar, where quartz was predominant (42-35%). In the grain size analysis, Puerto Cuatreros was characterized by the dominant presence of the fine size fraction; sandy silts and clayey silts (<0.05 mm) and Villa del Mar for the medium size; medium sands and fine sands (0.05-1mm). Sediments removed by biological activity in both study sites were similar in mineralogical composition than control sediments, but they were enriched with clay material and abundant organic vegetal material, mainly due to bioturbation work of crabs. The mean density of burrows of Neohelice granulata in Puerto Cuatreros was higher than Villa del Mar. The hardest minerals (such as quartz and feldspar) were in greater proportion in places not removed by crabs; so we can predict that they select sectors to mobilize and build burrows in substrates with lower hardness, which they can easily dig. These combinations of features were reflected in Puerto Cuatreros. The generic distribution of sedimentary materials is a direct consequence of the dynamics of the environment. In Bahía Blanca estuary, vegetation dissipates the energy of the water entering and bioturbator species, like Neohelice granulata, contribute to increase fine particles in the intertidal.

Keywords : Biosedimentation; Bioturbation; Mineralogy; Neohelice granulata; Bahía Blanca estuary.

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