Morphological analysis
Diatom frustules were cleaned with 30% v/v hydrogen peroxide and
hydrochloric acid following standard methods (European Standard EN 13946
2003). Permanent slides were mounted using Naphrax (refractive index of
1.74). At least 400 frustules were identified and counted in each sample
under light microscopy using an Olympus BX60 microscope, according to
Krammer & Lange-Bertalot, 1986a; Krammer & Lange-Bertalot, 1986b,
Kramer & Lange-Bertalot, 1991a; Kramer & Lange-Bertalot, 1991b and
Lange-Bertalot et al., 2017.