Trace elements composition of water samples collected.

<p>Chemical concentrations are in µg L⁻¹. n.a.: not analyzed.</p

Library coverage estimations and sequence diversity of 16S rRNA.

<p>*Library coverage was calculated as C = 1-n/N, where n is the number of OTU₉₇ without a replicate, and N is the total number of sequences.</p><p>**Shannon diversity index calculated using PAST.</p

Vertical profiles (in mg L⁻¹) of HCO₃⁻, NO₃⁻, SO₄²⁻, NH₄⁺, Fe_tot and Mn in Lake Hule (a) and Lake Río Cuarto (b).

<p>Vertical profiles (in mg L⁻¹) of HCO₃⁻, NO₃⁻, SO₄²⁻, NH₄⁺, Fe_tot and Mn in Lake Hule (a) and Lake Río Cuarto (b).</p

Chemical composition (µmol L⁻¹) and total pressure (pTOT; in atm) of dissolved gases (CO₂, N₂, CH₄, Ar, O₂, Ne, H₂ and He) and δ¹³C-CO₂ (expressed as ‰ V-PDB), δ¹³C-CH₄ (expressed as ‰ V-PDB), δD-CH₄ (expressed as ‰ V-SMOW) and R/Ra values of gas samples collected.

<p>Dissolved gas concentrations are in µmol L⁻¹. n.a.: not analyzed; n.d.: not detected.</p

Map of Costa Rica with the location of Hule and Río Cuarto lakes. Modified after Alvarado <i>et al.</i>[18].

<p>Map of Costa Rica with the location of Hule and Río Cuarto lakes. Modified after Alvarado <i>et al.</i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102456#pone.0102456-Alvarado1" target="_blank">[18]</a>.</p

Vertical distribution of δ¹³C-CO₂ and δ¹³C-CH₄ of Lake Río Cuarto.

<p>See the text for further details.</p

DGGE analysis performed on the bacterial 16S rRNA gene, showing the structure of the bacterial community inhabiting freshwater samples collected from the Hule and Río Cuarto lakes (a); taxonomic identification of bacterial 16S rRNA sequences excised from DGGE bands cut from the Lake Hule and Río Cuarto water profiles (b).

<p>DGGE analysis performed on the bacterial 16S rRNA gene, showing the structure of the bacterial community inhabiting freshwater samples collected from the Hule and Río Cuarto lakes (a); taxonomic identification of bacterial 16S rRNA sequences excised from DGGE bands cut from the Lake Hule and Río Cuarto water profiles (b).</p

Spider-diagrams, where concentrations of selected trace elements in Lake Hule (a) and Lake Río Cuarto (b) maximum depths are normalized to those measured in basalt rock samples collected from the young intra-caldera cone at Laguna Hule [80].

<p>Spider-diagrams, where concentrations of selected trace elements in Lake Hule (a) and Lake Río Cuarto (b) maximum depths are normalized to those measured in basalt rock samples collected from the young intra-caldera cone at Laguna Hule <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0102456#pone.0102456-Prosser1" target="_blank">[80]</a>.</p

Vertical profiles (in µmol L⁻¹) of CO₂, N₂, CH₄ and O₂ in Lake Hule (a) and Lake Río Cuarto (b).

<p>Vertical profiles (in µmol L⁻¹) of CO₂, N₂, CH₄ and O₂ in Lake Hule (a) and Lake Río Cuarto (b).</p

List of the taxonomic groups, identified according to the results if the 16S rRNA pyrosequencing, composing the archaeal communities in the freshwater samples collected along the depth profiles of the Hule and Río Cuarto lakes.

<p>Uncl: unclassified. Cand: Candidatus. Results are expressed in % with respect to the total archaeal community.</p