Determination of an Appropriate Approach to the Cleaning Methodology of Formalin Preserved Diatom Samples from the Northern California Coast

Nathaniel Kristan, United States and Christine Cass, Humboldt State University, Oceanography, Arcata, CA, United States
Diatoms play an important role as the dominant primary producer in many aquatic environments globally, anchoring the base of the food web and functioning as bioindicators. Diatom species can be identified by either their gross morphology or by more minute details in their valve microstructures. Identification of marine diatoms is particularly challenging, as the presence of salts in samples can obstruct visual identification efforts. A total of 12 different cleaning methodologies previously used by researchers will be compared. Six of the methodologies involve differential heating of the diatom samples in a muffle furnace from 450-560℃ for 15 to 30 minutes. The remaining six involve exposing the sample to a variety of differing combinations of heat (85-110℃), heavy oxidizers (30% hydrogen peroxide, potassium dichromate, and potassium permanganate), and strong acids (nitric acid, sulfuric acid, oxalic acid) in order to remove any biological material and leave only the valves. The aim of this project is to determine which method results in the clearest view of the diatom valves while simultaneously maintaining the valve structure. This will be determined by counting damaged and obscured valves and recording the percentage of such valves within each sample. An ANOVA will be used to determine any significant differences between the cleaning methodologies. Preliminary results indicate that the reduced mechanical stress of oven cleaning maintains the finer valve morphology, but that rinsing of marine samples with deionized water is a necessity for the combustion method to remove excess salt. Methodological tests are ongoing and will be completed by November 2019.