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.

Methods
The modern data in this dataset were collected in the 2016 lake survey. Surface sediment samples were taken using a stainless steel grabber. Lab analysis was conducted at Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences. Data of the sediment cores were from published literature through personal communication. The age-depth models of the cores were attached as a supplementary document of the related article. The diatom species or genre when ambiguous (indicated as “sp.”) were identified under microscope, and at least 300 valves were counted in each sample. The relative abundance of diatoms was shown in percentage. The environmental data were all standardized so that each column has a mean at zero and an SD at one. Environmental variables with 'sur_' in the name were measured from surface sediment while the same element might have been measured in water samples. For example, sur_TN means total nitrogen concentration in the surface sediment while TN means total nitrogen concentration in water.