Quantification of microbial mat response to physical disruption in siliciclastic sediments

PERILLO, VANESA L.; CUADRADO, DIANA G.; PAN, JERÓNIMO

ESTUARINE COASTAL AND SHELF SCIENCE

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2019 vol. 230 p. 1 - 11

0272-7714

Microbially-colonized sediments tend to be more resistant to erosional events than mostly abiotic sediments. However, the effect of complex microbial associations, such as microbial mats over sediments and the protection they offer, has not been extensively explored partly due to the difficulty that studies considering the consortia in toto pose. This difficulty prompts the gathering of an approximation to rheological properties of microbially-colonized sediments mostly through lab cultures of single-species or in less complex associations such as biofilms. The aim of this paper was to experimentally study the rheological properties of microbial mat communities from the semi-arid supratidal plain of Paso Seco (Argentina), under winter- and summer-like conditions, and with an altered mat structure (sterilized of living microorganisms), along with a biophysical characterization of the mats. Each test consisted in either penetrating, incising or compressing the microbial mat surface. Mats were able to bear maximum pressures ranging between 153 kPa and 3,725 kPa, depending on the probe assayed. In spring-collected samples, the cyanobacterium morphospecies Schizothrix sp. was dominant, while in winter-collected samples, the sheathed morphospecies Microcoleus chthonoplastes dominated. We found that when subjected to experimental drying (desiccated mat) microbial mats were harder to penetrate but easier to compress (by ~ 22%) than untreated microbial mats (winter-like conditions), due to the lack of moisture in the former condition. The incisiveness and penetration probes were able to penetrate to a greater depth in desiccated mats, while the inverse was found for the compression probe. Sterilization of the mat (by autoclaving) resulted in less force needed to penetrate the mat than in unaltered mats. These findings have implications for ichnology, on the interpretation of the conditions under which tracks and different features found in preserved sediments from paleoenvironments might have developed.