Aragonite crystallization in a sulfate-rich hypersaline wetland under dry Mediterranean climate (Laguna Honda, eastern Guadalquivir basin, S Spain)

Antonio Medina-Ruiz; Juan Jiménez-Millán; Isabel Abad; Antonio Gálvez; María José Grande; Rosario Jiménez-Espinosa

doi:10.1016/j.scitotenv.2024.171362

Aragonite crystallization in a sulfate-rich hypersaline wetland under dry Mediterranean climate (Laguna Honda, eastern Guadalquivir basin, S Spain)

Sci Total Environ. 2024 Apr 20:922:171362. doi: 10.1016/j.scitotenv.2024.171362. Epub 2024 Feb 29.

Authors

Antonio Medina-Ruiz¹, Juan Jiménez-Millán², Isabel Abad¹, Antonio Gálvez³, María José Grande³, Rosario Jiménez-Espinosa¹

Affiliations

¹ Department of Geology and CEACTEMA, University of Jaén, Campus Las Lagunillas, 23071 Jaén, Spain.
² Department of Geology and CEACTEMA, University of Jaén, Campus Las Lagunillas, 23071 Jaén, Spain. Electronic address: jmillan@ujaen.es.
³ Microbiology Division, Department of Health Sciences, University of Jaén, Campus Las Lagunillas, 23071 Jaén, Spain.

PMID: 38428615
DOI: 10.1016/j.scitotenv.2024.171362

Abstract

This research investigates the influence of water composition, the presence of seasonal algal mats, detrital inputs and the activity of microorganisms on the crystallization of aragonite in the sediments deposited in the hypersaline Laguna Honda wetland (S of Spain). The high alkaline and hypersaline waters (pH > 9.2 and C.E. > 70 mS/cm) of the wetland lake are rich in SO₄^2- (>24,000 mg/l), Cl^- (>21,000 mg/l), Na⁺ (>11,000 mg/l) Mg²⁺ (>8400 mg/l) and Ca²⁺ (>1000 mg/l), and are supersaturated for dolomite, calcite and aragonite. Sediments have lower pH values than column waters, oscillating from 8.54 in the low Eh (up to -80.9 mV) central deep sediments and 6.33 in the shallower higher Eh (around -13.6 mV) shore sediments. Erosion of the surrounding olive groves soils produced detrital silicates rich sediments with concretions of carbonate or sulfate. Aragonite (up to 19 %) and pyrite (up to 13 %) are mainly concentrated in the organic matter rich samples from the upper part of the sediment cores, whereas gypsum is preferably concentrated in low organic matter content samples. Mineral crusts containing a MgAl silicate phase, epsomite, halite and gypsum are precipitated on the floating algal mats covering the wetland waters. Floating algal mats deposit increased the organic matter content of the upper sediments which promoted the presence of fermentative microorganisms, sulfate-reducing bacteria (SRB) and sulfur-oxidizing bacteria (SOB) communities and variations of Eh that influence the authigenesis of carbonate and S-bearing minerals. Replacement of poorly crystalline MgSi phases infilling algal cells by aragonite was favored in the organic matter rich sediments with low Eh values and important SRB communities that promoted sulfate bioreduction processes to form pyrite. Aragonite precipitation was favored by the increase of carbonate and bicarbonate concentration produced by the SRB oxidation of organic matter, the CO₂ degassing by high summer temperatures and the CO₂ uptake by photosynthesis of the algal mats.

Keywords: Aragonite; Bacterial community; Hypersaline wetland; Laguna Honda; S-bearing minerals; Wetland sediment.