Diatom biodiversity and distribution on wetwalls in Great Smoky Mountains National Park

Diatoms and other algae were collected and identified from subaerial habitats (wetwalls) in Great Smoky Mountains National Park as part of a larger biodiversity survey of the Park. Algal collections were made across a range of moisture gradients and bedrock mineralogics with pH ranging from 3.8 to 7.7. None of the communities collected were entirely submerged in water, but were often associated with moist bryophytes, cyanobacterial mats, and dripping groundwater seeps. Some of the collections were from cliff faces wetted only periodically. To date, 41 diatom genera and over 223 species have been identified from these habitats. Several of these genera are widely distributed across aquatic habitats; however, several of the genera are "subaerial specialists" and possess morphological features such as reduced size, reduced external openings in the cell wall, or additional external siliceous membranes that allow them to survive in relatively dry habitats. Widely distributed species with high fidelity to subaerial habitats occur in the genera Achnanthes, Cymbopleura, Decussata, Diadesmis, Luticola, Melosira, Microcostatus, Nupela, Psammothidium, and Orthoseira. Many of the species constitute new Park records, national records, or are new to science.