Lake morphology as an important constraint for benthic diatoms in temperate, humic forest ponds

Small lakes are among the most threatened ecosystems in the world. Their protection is of crucial importance since they support an unusually high biodiversity relative to their size. The present study aimed at selecting the main drivers, especially the role of the morphological variables, shaping benthic diatom communities in unique, but rarely investigated forest pond ecosystems in the temperate region, using traditional (species-based methods and diversity indices) and novel approaches (trait-based methods and functional diversity indices) of diatom ecology. Therefore, we analyzed the effects of the environmental (temperature, conductivity, colour, shading, pH, nutrient forms, anions) and morphological (surface area, depth) variables of 70 temperate, forest ponds located in two regions of Hungary on the composition (species-and trait-based) and diversity (traditional and functional) of their benthic diatom communities. Based on the multivariate analyses, no regional differences in the environmental and morphological variables were been observed among the ponds. Our results showed that both environmental variables and lake morphology had significant effects on the benthic diatom communities, but they contributed to their variation with different proportions. Environmental variables such as nutrient content (rsoluble reactive phosphate = 0.72) and conductivity (r = 0.65) affected mostly the species composition, and the traditional diversity metrics (rtotal phoshate =-0.42, rconductivity = - 0.54). In contrast, morphological features of the ponds were the most important drivers of diatom trait composition. This functional response of diatoms manifested in the selection of species according to their size, shape and lifeforms, moreover, in changing of functional diversity. Overall, this study revealed the complex interplay between environmental variables and lake morphology in shaping the composition of benthic diatom communities. Furthermore, it highlights the necessity to apply different methods to understand the ecology and functioning of these special aquatic ecosystems.