Periphytic algal assemblages along environmental gradients in the rivers of the Lake Ladoga basin, Northwestern Russia: implication for the water quality assessment

The purpose of this study was to examine the role of geological, hydrological, and anthropogenic factors in structuring periphytic algal assemblages in the rivers of the Lake Ladoga basin (Northwestern Russia). Canonical correspondence analysis (CCA) conducted on spring dataset showed that water temperature, color, and river morphology were primary factors shaping the structure of algal assemblages during the spring post-flood period. CCA on summer and autumn dataset revealed that conductivity and total phosphorus were the most important variables during the base flow period. Cluster analysis carried out on algal assemblages separated all rivers into two main groups that corresponded to the two geomorphological regions of the Lake Ladoga basin: the northern and the southern sub-basins. The separation of the northern and the southern groups were best explained by the pattern of conductivity reflecting geological and land use differences in the watersheds. The values of the Specific Pollution sensitivity Index (IPS) and the Biological Diatom Index (IBD) were higher, indicating better water quality, for rivers of the northern sub-basin than for rivers of the southern sub-basin. Mean values of the IPS and IBD for rivers of the northern and the southern sub-basins varied within the boundaries of a good water quality.