Microbial mat contribution to the formation of an evaporitic environment in a temperate-latitude ecosystem

PERILLO, VANESA LILIANA; MAISANO, LUCÍA; MARTINEZ, ANA MARÍA; QUIJADA, ISABEL EMMA; CUADRADO, DIANA GRACIELA

JOURNAL OF HYDROLOGY

ELSEVIER SCIENCE BV

Año: 2019 vol. 575 p. 105 - 114

0022-1694

An evaporitic environment is characterized by having high salinity, climatic, and hydrological factors thatpromote a negative water balance; however, biological factors may also influence their development. Moderncoastal flat Paso Seco (40°33′S; 62°14′W) is located in a semi-arid region with low precipitation and dry windscoming mainly from the NW. The site is an old tidal channel, which nowadays behaves like a shallow coastalsaline-like basin, separated from the sea by a sand barrier, which the sea periodically overcomes, flooding theflat with eventual water evaporation. Microbial mats of up to 1 cm thick colonize the sandy sediments of thisevaporitic environment. Water samples were taken during five field trips (2017?2018) from interstitial water ofthe flat, a tidal creek that crosses the flat, and two shallow tidal depressions (TDs) within the flat with differentdegrees of evaporation. In comparison to the sea, the maximum salinity values measured in Austral spring(September 2017) in the tidal creek were doubled, tripled in interstitial water, and 5.9 to 8 times higher in TDs.Ionic concentration denotes that evaporite chemical divides are followed as water evaporates, corresponding tothe presence of CaCO3, gypsum and halite found in TDs. On-site permeability of microbial mat-covered surfacespresented semi-pervious properties. Microbial mat presence is condition for CaCO3, gypsum, and halite precipitationas they allow for water retention and its consequent evaporation due to the impermeability they conferto the sedimentary surface. Thus, microbial mats are a biological factor affecting the development of an evaporiticenvironment.