DIATOM COMMUNITY STRUCTURE ALONG PHYSICOCHEMICAL GRADIENTS IN SALINE LAKES

Relationships between diatom assemblages and physicochemical factors w ere examined in 63 saline lakes in western North America. Sodium was t he overwhelmingly dominant cation in the lakes examined; lakes above 4 7-degrees latitude were dominated by SO4-2, and lakes below 47-degrees were dominated by CO3-2 and Cl-1. This latitudinal gradient for anion s was correlated with the distribution and community structure of diat oms. Sixty-two taxa comprised > 85% of the total diatom relative abund ance in the saline environments. There were strong negative correlatio ns between specific conductance and diversity and species richness, ho wever pH and major cations showed limited predictive value. Cluster an alyses identified diatom assemblages along specific conductance and ma jor 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 condi tions in lacustrine ecosystems. Greatest diversity was found in habita ts 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 communi ty structure suggested that shallow saline lakes may have provided evo lutionary pathways for speciation of marine pennate diatoms into athal assic (nonmarine) environments.