On the biodiversity of diatom communities in lakes of east China: Geochemical effects dominated after eutrophication

Aim: Over the last century, lakes all over the world have experienced
significant eutrophication and become more susceptible to critical
transitions. This has prompted a growing need to understand how community
dynamics shift following ecological perturbations. This study aims to
elucidate the present status, spatial patterns and determinants of
biological diversity, and how they have changed in response to alterations
driven by eutrophication. Location: Lakes of East China, mostly in the
Yangtze River Basin Taxa: Bacillariophyceae (163 species in 33
genres)  Methods: The environmental conditions of over sixty
lakes were assessed based on parameters such as water quality, physical
characteristics and biogeochemical constituents. Surface sediment samples
and high-resolution sediment records were collected to quantify the
biodiversity of diatom communities, and Principle Component Analysis (PCA)
was used to determine the major environmental gradients. Meanwhile, linear
regression, Canonical Correlation Analysis and Mantel tests were used to
quantify the correlations between variables. Results: Biodiversity metrics
showed no distinct geographic patterns, although areas near large lakes
showed comparatively high evenness. Smaller pairwise dissimilarities were
observed among hypereutrophic lakes in comparison to lakes with a lower
trophic status. The past century has witnessed a decrease in both pairwise
dissimilarity and the standard deviation of Evenness. A significant
statistical association was found between dissimilarity and ionic
concentration and composition in the surface sediment of lakes, rather
than nutrient levels. Main conclusions: Following regional eutrophication
and human disturbance, a significant reduction in biodiversity
differentiation was observed in lakes located in East China. Currently,
the dominant factor in determining the beta diversity of diatom
communities is geochemical conditions rather than nutrient concentrations.
Long-term stress caused by cultural eutrophication may also have altered
the dominant determinant of regional biodiversity and diatom community
dynamics.