INFLUENCE OF NUTRIENT ENRICHMENT ON STRUCTURING DIATOM COMMUNITIES IN A GLACIAL MELTWATER STREAM, MCMURDO DRY VALLEYS, ANTARCTICA

In the arid McMurdo Dry Valleys of East Antarctica, glacial meltwater streams flow for 6-10 weeks during the austral summer. Harbored in these meltwater streambeds are diatom communities, which are part of a microbial mat matrix. These mat assemblages endure desiccating winters and become reactivated upon rehydration during the austral summer. Water is considered the major limiting resource in the dry valley stream ecosystems, and the variable flow of meltwater has been shown to regulate the biomass and growth of these algal mats. However, other environmental variables could influence the structure of these mat communities. In this thesis, the influences of nutrients are examined as a regulatory control on diatom community structure. This thesis draws from previous experimentation using Nutrient Diffusing Substrates (NDS) with nitrate and phosphate amendments that were left in Green Creek for algae to colonize. Characterization of diatom communities that grew on NDS units showed that nitrate enrichments significantly altered diatom relative abundance, with an increase in Fistulifera pelliculosa to 21% relative abundance in nitrate treatments compared to other nutrient amendments, which had less than 5% F. pelliculosa abundance. Other nutrient amendments showed only a marginal influence on diatom relative abundance. In addition, nitrate and phosphate amendments showed greater average diatom densities relative to the control treatments, with the greatest densities occurring in nitrate amendments. These results suggest that nutrients influence diatom growth and accrual, although stream hydrology and geomorphology likely have a greater influence on regulating the structure of these diatom communities within the microbial mat matrix. Moreover, the results from this thesis can help to predict the response by diatom communities to expected landscape changes in McMurdo Dry Valley streams as a function of climate change, such as increase flow and subsequent nutrient enrichment