Benthic diatoms on fluvial tufas of the Mesa River, Iberian Range, Spain

Abstract

Background. The Mesa River (MR) in the Iberian Range (Spain) displays prominent, Pleistocene to present-day fluvial
tufa deposits. Little of their associated microbiota has been studied to date despite the regional and historical relevance
of these calcareous buildups. Goals. This paper is a preliminary exploration of the diatom (Bacillariophyta) genera
associated with actively-growing tufa from 10 benthic environments along 24 km of the Mesa River. Methods. Brightfield
microscopy, as well as consultation with specialists and specialized literature was used for taxonomic classification
of diatoms. Results. We identified 25 diatom genera in three different types of sedimentary facies (porous and
moss-algae rich, dense-laminated, and tufa-free gravel). Most diatoms were raphid pennate (class Bacillariophyceae),
while a few were centric (class Coscinodiscophyceae) or araphid pennate (class Fragilariophyceae). They appeared as
integral components of the tufa structure along with cyanobacteria and other algae and mosses. Conclusions. Together
with previous studies on the hydrochemistry and sedimentology of the MR, our interpretations suggest that HCO3
-,pCO2, Ca2+, and TDIC negatively affect diatom richness and that their abundance is positively related to the presence
of mosses and algae.