Diversity and geochemical structuring of bacterial communities along a salinity gradient in a carbonate aquifer subject to seawater intrusion

• Published in: FEMS microbiology ecology Vol. 90; no. 3; pp. 922 - 934
• Main Authors: Héry, Marina, Volant, Aurélie, Garing, Charlotte, Luquot, Linda, Elbaz Poulichet, Françoise, Gouze, Philippe
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.12.2014; Oxford University Press; Wiley-Blackwell
• Subjects: 16S rRNA gene; Acidification; Aquifers; Bacteria; Bacteria - classification; Bacteria - genetics; bacterial communities; bacterial diversity; Base Sequence; Biodiversity; Biogeochemistry; Calcite; carbon; Carbon dioxide; Carbonates - metabolism; Chemical analysis; Coastal aquifers; Community composition; community structure; Correlation analysis; Earth Sciences; Ecology; Environmental Sciences; Fresh Water - microbiology; freshwater; freshwater–saltwater mixing zone; genes; Genes, rRNA; Geochemistry; Global Changes; Groundwater - microbiology; High-Throughput Nucleotide Sequencing; Microbial Consortia; Microbiology; microorganisms; mixing; Multivariate analysis; Organic acids; organic acids and salts; Organic carbon; oxidation; pyrosequencing; Relative abundance; ribosomal RNA; RNA, Ribosomal, 16S - genetics; Saline water; Saline water intrusion; Saline-freshwater interfaces; Salinity; saltwater intrusion; Sciences of the Universe; Seawater; Seawater - microbiology; Sequence Analysis, DNA; subterranean estuary; Water analysis; Water Microbiology; bacterial diversity; freshwater–saltwater mixing zone; pyrosequencing; subterranean estuary; 16S rRNA gene; freshwater-saltwater mixing zone
• ISSN: 0168-6496; 1574-6941; 1574-6941
• DOI: 10.1111/1574-6941.12445

Abstract In aquifers subject to saline water intrusion, the mixing zone between freshwater and saltwater displays strong physico-chemical gradients. Although the microbial component of these specific environments has been largely disregarded, the contribution of micro-organisms to biogeochemical reactions impacting water geochemistry has previously been conjectured. The objective of this study was to characterize and compare bacterial community diversity and composition along a vertical saline gradient in a carbonate coastal aquifer using high throughput sequencing of 16S rRNA genes. At different depths of the mixing zone, stable geochemical and hydrological conditions were associated with autochthonous bacterial communities harboring clearly distinct structures. Diversity pattern did not follow the salinity gradient, although multivariate analysis indicated that salinity was one of the major drivers of bacterial community composition, with organic carbon, pH and CO2 partial pressure. Correlation analyses between the relative abundance of bacterial taxa and geochemical parameters suggested that rare taxa may contribute to biogeochemical processes taking place at the interface between freshwater and saltwater. Bacterial respiration or alternative metabolisms such as sulfide oxidation or organic acids production may be responsible for the acidification and the resulting induced calcite dissolution observed at a specific depth of the mixing zone. Distinct bacterial communities are shaped by physico-chemical gradients in the freshwater-saltwater mixing zone of an aquifer. The wide range of their potential metabolic capacities can impact the groundwater geochemical properties. Distinct bacterial communities are shaped by physico-chemical gradients in the freshwater-saltwater mixing zone of an aquifer. The wide range of their potential metabolic capacities can impact the groundwater geochemical properties.