Quantification of microbial mat response to physical disruption in siliciclastic sediments

Abstract

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, have 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, along with a bio-physical characterization of the mats. Each test consisted in either penetrating, incising or compressing the microbial mat surface. They were able to bear maximum pressures ranging between 1.53 kg cm-2 and 37.25 kg cm-2, depending on the probe assayed. During warmer temperatures, the cyanobacterium morphospecies Schizothrix sp. was dominant in the samples, while during winter-like conditions, the sheathed morphospecies Microcoleus chthonoplastes dominated. We found that under warmer conditions (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 forthe compression probe. 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.