For richer or poorer: diatoms as indicators of biological condition across a gradient of boreal fen types

The goals of this study were to (1) document spatial and temporal variation in diatom species composition across a gradient of northern peatlands and (2) determine how underlying environmental conditions influence diatom species distribution. We sampled three peatlands (a rich, moderate, and poor fen) in interior Alaska during a growing season (May until August). A total of 100 species were observed across all fens, 17 of which were present at > 1% relative abundance, and 15 were selected as indicator species. Based on the differential response of Simpson vs. Shannon diversity metrics, we determined that fen type affected diatom assemblage composition and differences were driven by changes in the most common, but not in the least common species. Diatom species richness declined along a gradient of rich to poor fens. Conductivity, dissolved organic carbon concentration, water temperature, pH, and water depth explained 63% of the total variation in diatom assemblage structure among fens. We identified unique indicator species associated with each fen that either reinforced or expanded current understanding of their environmental thresholds. These results indicate that variation in environmental conditions in boreal fens will be reflected in diatom assemblages, which may be used to monitor biological condition in these ecosystems.