Moisture is an important factor in structuring algal communities.  The presence and availability of water will determine the species present and the abundance of these species.  Wetwall habitats provide a different environment for algal species compared to other aquatic habitats.  These wetwall habitats often experience times of drying, from occasional drying to frequent and possible daily drying.  The taxa present in these communities must be able to tolerate periods of low or no moisture.   We predict that as communities are exposed to periods of desiccation, the species composition will transition from typically aquatic taxa to wetwall specialist taxa.
Algal communities were sampled from wetwalls and streams in the Great Smoky Mountains National Park.  Samples were grown in the laboratory on stone tiles in Z8 medium.  After establishing for one month, these communities were exposed to a series of desiccation and rehydration events.  Desiccation periods included 0, 6, 24, 168 hour and one month treatments.  The community data were analyzed to examine the impact of desiccation on community structure and composition.  At higher levels of desiccation, taxa considered to be typically aquatic, i.e. Mougeotia sp., decreased in abundance while those considered more adaptable to drier environments, i.e. Diadesmis sp., increased.