The aim of this study is to characterize the current spatial distribution of three main phyla of phytoplankton (Cyanobacteria, Charophyta and Chlorophyta) from 77 Latvian lakes and ponds, analysed from modern surface sediment samples through a non-pollen palynomorph approach. The Pearson cross-correlation and the principal component analysis were applied to test the potential correlation of phytoplankton with climate (mean winter and summer temperature), water (pH), environmental (land use – forest, agriculture and urban) and sediment (organic and carbonate matter) variables. The results show the dominance of Chlorophyta in Latvian lakes and ponds. Cyanobacteria were dominant in sites closer to human-populated and recreation centres, including urban and agricultural land-use areas. In more turbid and polluted environments, Chlorophyta thrive today. Charophyta dominated in forested areas. Although Chlorophyta dominate in present-day waterbodies, the rather high relative proportion of Cyanobacteria draws attention to a potential threat. As the cross-correlation results indicate a negative correlation between Cyanobacteria and mean winter temperatures, in warmer climates Cyanobacteria can overtake other phytoplankton. The results of this study can be further used in lake and pond management.
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