Assessing the efficiency of low-cost cleaning methods for diatoms from intertidal sediment samples

This study aims to compare the effectiveness of several low-cost reagents in obtaining high-quality diatom slides for microphytobenthos research. We evaluated the performance of eight reagents in sediment samples of beach intertidal zones. For each of the tested reagents, different pre-treatment conditions (pre-washed; non-washed) and three different temperatures (room temperature at 26 °C, 60 °C, and 100 °C) were also evaluated. For each treatment (combinations between reagents, temperatures, and pre-treatment conditions), we counted diatoms cells that met the criteria necessary for taxonomic identification (Whole/Half frustules or valves without cell material) in 30 randomly chosen fields of view in definitive preparations made from the treated samples. We also compared the treatments regarding species richness and diversity observed in the definitive preparations. The reagents influenced more the conditions of diatoms cells than the temperature and pre-treatment. H₂O₂, HNO₃, NaClO were the methods that had the best performance in relation to the number of identifiable items. The six treatments with H₂O₂ presented similar amounts of identifiable items, regardless of pre-treatment and temperature. HNO₃ presented a higher number of identifiable items in non-washed and pre-washed treatments at 60 °C and non-washed at 100 °C. NaClO had its best performance the following treatments: non-washed at room temperature and non-washed and pre-washed at 60 °C. H₂O₂ and HNO₃ also showed better results for diatom species richness and diversity, followed by NaClO. The use of H₂O₂ was more robust since it obtained good results regardless of temperature and pre-treatments and should be preferred. HNO₃ and NaClO should be used only with the appropriate temperatures, and pre-washing should be avoided.