Microbe-physical interactions determine the nature of epibenthic microbial mats and associated sedimentary structures in a hypersaline continental saltpan

Abstract

Salitral de La Vidriera (38° 44′ S; 62° 34′ W) saltpan was a tidal flat occupying the innermost section of the Bahía Blanca estuary before its isolation ~ 4500 years BP. With no current marine influence it is a hypersaline evaporitic environment. Provided the uniqueness of this endorheic basin fed only by rainfall, we characterized the microbial colonization of surface sediments by epibenthic mats from a geobiological perspective; and explored causal relationships between the microbially induced sedimentary structures (MISS) formed and topographic zonation and water availability. Filamentous and coccoid cyanobacteria were the dominant prokaryotes in terms of autotrophic biomass in mats and MISS. Pennate diatoms were the dominant microeukaryotes; Archaea were present. The dominant photoautotrophs have a preeminent role incorporating organic matter into sediments, thus turning this ecosystem into a carbon sink. The bio-sedimentary ecosystem grows by pulses mainly in response to the presence of accumulated rainwater in the saltpan, as the microbial biomass was significantly higher after rain episodes, either in summer or winter. Therefore, water presence allows the development of growth structures during calm conditions. An increase in environmental energy physically disrupts the mat, creating MISS such as rolled-up mat, flipped-over mat, folds, and wrinkles analogous to those found in coastal settings.