Diatoms are useful indicators of ecological conditions but the mechanisms driving assemblage distribution are not clearly defined. Understanding the mechanisms underlying assemblage distribution is necessary to make accurate predictions about the effects of environmental change, such as hydrologic management, restoration, and climate change. The examination of diatom distribution and key drivers across a large wetland over several years can provide a resolved spatio-temporal framework for determining the relative importance of environmental and spatial factors influencing assemblage patterns. I examined a 6-year record of diatom distribution across the Everglades, a large hydrologically-managed subtropical wetland. Successful restoration of this ecosystem depends on using reliable ecological targets and bioassessment strategies based on a comprehensive understanding of the biotic responses to the variables being manipulated, especially hydrology. The components of my research are: 1) characterizing the relationship between diatom distribution and environmental factors; 2) investigating the taxonomy of species presumably with little or no limitation to dispersal by spatial factors; and 3) examining the relative importance of environmental and spatial factors on diatom distribution patterns within a hydrologically-managed environment. Building upon the well-documented utility of Everglades diatom transfer functions for phosphorus based on species optima and tolerance ranges, I developed transfer functions for hydroperiod and biovolume of periphyton (consortium of algae, bacteria, and fungi) and evaluated the utility of resultant diatom-based inference models for bioassessment. Considering the importance of environmental factors, diatoms in the Everglades and Caribbean wetlands may have restricted distributions. My taxonomic investigation of two species with presumed continental distributions and the consequent description of two new species suggest spatial factors can restrict diatom dispersal. The importance of both environmental and spatial controls on Everglades diatom distribution may be related to the availability of calcareous (high mineral content) periphyton that diatoms inhabit because periphyton mineral content is correlated with environmental factors, which differ among compartments within the ecosystem because of hydrologic management. I found environmental factors were more important controls on the distribution of persistent inhabitants of calcareous periphyton, suggesting spatial factors are relatively less important when species are well-suited to the habitats made available by environmental conditions influenced by hydrologic management.
