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Iberian Pit Lake Stratified Community

Ecological State STABLE
Environment acid mine drainage
ENVO:00002186
Source File Iberian_Pit_Lake_Stratified_Community.yaml

A permanently stratified (meromictic) acidic pit lake community from the Iberian Pyrite Belt in southwestern Spain/Portugal, distinguished by dramatic vertical metabolic zonation and subsurface anaerobic processes in an extreme acid mine drainage environment. The pit lake ecosystem exhibits three distinct layers: an upper oxic mixolimnion (pH 2.2-3.1, 0-3m depth), a chemocline transition zone (11m), and an anoxic monimolimnion (pH 3.0-4.5, 35m depth). The upper layer is dominated by acidophilic green algae (Coccomyxa onubensis) and heterotrophic bacteria (Acidiphilium), while the chemocline hosts intense sulfate reduction and iron cycling by specialized Proteobacteria (Desulfomonile, Candidatus Acidulodesulfobacterium). The deep anoxic layer harbors archaeal heterotrophs (Thermoplasmatales, 46% of sequences) that scavenge organic carbon and perform sulfide oxidation using trace oxygen, along with iron-reducing bacteria (Geobacter) and subsurface methanogens (Methanobrevibacter, Methanospirillum). The permanent stratification creates steep geochemical gradients with iron concentrations increasing from 2 mM Fe³⁺ in surface waters to 113 mM Fe²⁺ at depth, sulfate ranging from 26-126 mM, and oxygen transitioning from oxic to completely anoxic conditions. This system represents a natural laboratory for studying coupled aerobic-anaerobic metabolism, metal cycling, biosulfidogenesis, and subsurface methanogenesis under polyextreme conditions (acidity, metals, anoxia). The Iberian Pyrite Belt pit lakes demonstrate how microbial stratification can support complex biogeochemical cycling and potential natural attenuation of toxic metals through sulfide precipitation.

Taxonomy

Taxon Ontology ID Functional Roles Abundance
Leptospirillum NCBITaxon:179
PRIMARY_DEGRADER
COMMON
Acidithiobacillus ferrooxidans NCBITaxon:920
PRIMARY_DEGRADER
COMMON
Desulfomonile NCBITaxon:2357
PRIMARY_DEGRADER SECONDARY_FERMENTER
DOMINANT
Candidatus Acidulodesulfobacterium NCBITaxon:2597222
PRIMARY_DEGRADER SECONDARY_FERMENTER
ABUNDANT
Thermoplasmatales NCBITaxon:2301
CROSS_FEEDER SECONDARY_FERMENTER
DOMINANT
Methanobrevibacter NCBITaxon:2172
SECONDARY_FERMENTER
RARE
Coccomyxa onubensis NCBITaxon:1125364
PRIMARY_PRODUCER
DOMINANT

Ecological Interactions

Stratified Iron Redox Cycling

MUTUALISM

Source Taxon: Leptospirillum

Metabolites: Fe(II) (CHEBI:29033), Fe(III) (CHEBI:29034)

Biological Processes:

Downstream Effects:
→ Biosulfidogenesis and Metal Precipitation

Evidence

  • PMID:36123522 - SUPPORT (IN_VIVO)
    "Addition of organic carbon and elemental sulfur should stimulate sulfate reduction and limit reoxidation of sulfide minerals"
  • PMID:36123522 - SUPPORT (IN_VIVO)
    "Geobacter expresses outer membrane cytochromes (OmcS, OmcB, TPM > 100)"

Biosulfidogenesis and Metal Precipitation

MUTUALISM

Source Taxon: Desulfomonile

Metabolites: sulfate (CHEBI:16189), hydrogen sulfide (CHEBI:16136), copper sulfide (CHEBI:75219)

Biological Processes:

Downstream Effects:
→ Subsurface Heterotrophic Carbon Scavenging

Evidence

  • PMID:36123522 - SUPPORT (IN_VIVO)
    "We argue that sulfide precipitation is not limited by microbial genetic potential but rather by the quantity and quality of organic carbon reaching the deep layer as well as by oxygen additions to the groundwater enabling sulfur oxidation"
  • PMID:36123522 - SUPPORT (IN_VIVO)
    "metal sulfide precipitation observed: copper sulfide (covellite), zinc sulfide (wurtzite), and arsenic sulfide (realgar)"

Subsurface Heterotrophic Carbon Scavenging

CROSS_FEEDING

Source Taxon: Thermoplasmatales

Biological Processes:

Downstream Effects:
→ Subsurface Methanogenesis

Evidence

  • PMID:36123522 - SUPPORT (IN_VIVO)
    "We argue that sulfide precipitation is not limited by microbial genetic potential but rather by the quantity and quality of organic carbon reaching the deep layer as well as by oxygen additions to the groundwater enabling sulfur oxidation"
  • PMID:36123522 - SUPPORT (IN_VIVO)
    "Algal biomass and dissolved organic carbon (0.44 mM in deep layer vs. 0.15-0.24 mM in upper layer) settle to deep waters"

Subsurface Methanogenesis

CROSS_FEEDING

Source Taxon: Methanobrevibacter

Metabolites: methane (CHEBI:16183), hydrogen (CHEBI:18276)

Biological Processes:

Evidence

  • doi:10.3390/microorganisms8091275 - SUPPORT (IN_VIVO)
    "Furthermore, the detection of reads classified as methanogens and Desulfosporosinus spp., although at low relative abundance, represents one of the lowest pH values (2.9 in LZ) at which these taxa have been reported, to our knowledge"
  • PMID:36123522 - SUPPORT (IN_VIVO)
    "Using a combination of amplicon sequencing, metagenomics and metatranscriptomics we performed a taxonomically resolved analysis of microbial contributions to carbon, sulfur, iron, and nitrogen cycling"

Environmental Factors

Factor Value Unit
Upper Layer pH 2.2-3.1 pH units
Deep Layer pH 3.0-4.5 pH units
Oxygen Stratification Oxic to anoxic stratification gradient
Iron Concentration Gradient 2-113 mM Fe
Sulfate Concentration 26-126 mM
Permanent Stratification Meromictic lake type
Microbial Diversity Gradient 72-206 ASVs per sample