Geothermal diatoms: seasonal variability in the El Tatio geothermal field (Altiplano, Chile)

Abstract

Diatom floras were examined in a high-altitude geothermal field, 4200 - 4500 m (29 degrees 19'S 68 degrees W'), located in the Central Andean dry Puna ecoregion or southern Altiplano. These locations include hostile environments subjecting living organisms to extreme conditions. The aim of the present study was to investigate the spatial patterns and describe the response of diatom assemblages to differences in physical and chemical variables. Different shallow (<10 cm) aquatic systems with variable chemical and physical conditions (fumaroles, freshwater-saline rivers and swamps) were studied seasonally during 2011-2012. The conductivity exhibited high variability (360 to 18340 FAS cm(-1) ) among the systems studied, temperature was lower in rivers and swamps (6.8 degrees C - 10 degrees C) and high in fumaroles stations (30 degrees C - 37.5 degrees C), and pH was lower in fumaroles than freshwater systems (3.25 to 8.97). Statistical analyses suggest that the diatoms cluster into three major groups. The most common taxa include: Achnanthidium exiguum (Grunow) Czarnecki, Cocconeis placentula var. lineata (Ehrenberg) Van Heurck, Eolimna minima (Grunow) Lange-Bertalot, Staurosirella pinnata (Ehrenberg) Williams and Round, Navicula gregaria Donkin, Nitzschia inconspicua Grunow, Nitzschia palea (Kutzing) Smith, Nitzschia perminuta (Grunow) Peragallo, and Planothidium lanceolatum (Brebisson ex Kutzing) Lange-Bertalot. As expected, the 20 to 200 Ina-size fraction contained the highest numbers of diatom taxa (53 species), although an unexpectedly high number (47 species) were also found in the smaller 5 to 20 Ina-size fraction, more associated to fumaroles and saline systems. The 180 to 2000 Ina size fraction contained only two species, including rosette-forming diatom Ulnaria ulna (Nitzsch) Compere, and the unicellular species Surirella chilensis Janisch, both species exclusively reported in freshwater systems. Canonical correspondence analysis (CCA) and Monte Carlo permutation tests showed clear correlations between species, conductivity, TP (total phosphorous), NO3-, HCO3, Mg2+, temperature and dissolved oxygen (DO). The gradient of ionic composition values explaining most variation in diatom assemblages ranged from waters dominated by Ca2+ and SO4- to waters with higher proportions of Na+, K+, F-, Li+, Mg2+ and Cl-. Other factors include substrate type, presence of macrophytes, current velocity and other local environmental conditions. The results presented here enhance our understanding of diatom richness/composition in hostile environments from a high-altitude arid and semi-arid geothermal region.