Diatom community structure along environmental and spatial gradients in lakes and streams

The aims of this study were to examine whether lentic and lotic diatom communities exhibit distinct groupings following habitat preferences and whether lentic and lotic diatom communities differ in terms of spatial structure at regional scales in Finnish Lapland. Principal Component Analysis (PCA) was used to describe the main gradients in water chemistry. Non-metric Multidimensional Scaling (NMDS) was used to examine patterns in diatom community structure. Redundancy Analysis (RDA) with variation partitioning was employed to examine the spatial structure of lentic and lotic communities. Principal coordinates of neighbour matrices was used to model the spatial variables in variation partitioning. The PCA showed that the main gradients in water chemistry of lakes and streams were relatively similar in the study area in northern Finland although the main PCA gradient was more related to water pH in lakes, whereas in streams the main PCA gradient was mainly related to alkalinity and conductivity. According to NMDS. however, the lake and stream diatom communities differed sharply. RDA with variation partitioning showed that pure spatial factors explained more of the explained variation for the streams (28 %) than for the lakes (9 %). Pure environmental factors nonetheless explained most of the variation both for the lakes (74 %) and streams (58 %). Our results lent support to a notion that diatoms are probably jointly structured by neutral, dispersal-related processes and species sorting by the environment. as both environmental and spatial factors had a notable effect on community structure. We emphasize though that local environmental control was overall much stronger than the effects of large-scale geographical and dispersal-related factors both in lakes and streams.