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.