Does size matter? Assessing the role of lentic system area on diatom diversity in subarctic Finland

Lentic systems are often small, experiencing a wide range of consequences of climate change through shifts in chemistry and community assembly processes. Such vulnerable systems support most of the regional freshwater biodiversity in the Finnish subarctic, highlighting their conservation value. Despite increasing research of subarctic freshwater diatoms focusing on the relationship between biodiversity and various factors, the effect of habitat size on benthic diatoms remains understudied. This study compared diatom diversity and water chemistry between and within subarctic lentic systems. Significant differences in species richness, water pH, conductivity, Ca, Cl, and Na were found between lakes and ponds, but the variation within systems was insignificant. Our results suggest that there were size-dependent differences in community composition, assembly processes, and local contributions towards beta diversity, and that differences in water chemistry between ponds and lakes help shape the benthic diatom communities. Thus, surface area may be used as a proxy for water chemistry. Microhabitat abundance and environmental harshness likely cause such area effects, but further investigation is required on isolation, dispersal limitations, and water depth. Studying the benthic communities of these vulnerable systems will provide insight into the effects of climate change.