DIATOM COMMUNITY STRUCTURE ALONG PHYSICOCHEMICAL GRADIENTS IN SALINE LAKES

Relationships between diatom assemblages and physicochemical factors were examined in 63 saline lakes in western North America. Sodium was the overwhelmingly dominant cation in the lakes examined; lakes above 47-degrees latitude were dominated by SO4-2, and lakes below 47-degrees were dominated by CO3-2 and Cl-1. This latitudinal gradient for anions was correlated with the distribution and community structure of diatoms. Sixty-two taxa comprised > 85% of the total diatom relative abundance in the saline environments. There were strong negative correlations between specific conductance and diversity and species richness, however pH and major cations showed limited predictive value. Cluster analyses identified diatom assemblages along specific conductance and major anion gradients. Indices for specific conductance and major anions were also developed for 62 diatom taxa. These diatom indices provide useful information to interpret past and present physicochemical conditions in lacustrine ecosystems. Greatest diversity was found in habitats with ionic concentrations < seawater and ion composition similar to marine environments. Principal components analyses comparing loadings for major cations and anions, ionic concentration, and diatom community structure suggested that shallow saline lakes may have provided evolutionary pathways for speciation of marine pennate diatoms into athalassic (nonmarine) environments.