Analysis of factors controlling epilithic diatom community compositions in subarctic lakes of Finnish Lapland
Albert, Raino-Lars; Korhola, Atte; Sorvari, Sanna
Distributional patterns of epilithic diatoms were examined in relation to environmental variables in 41 subarctic lakes distributed across two different geographical subregions of northern Finnish Lapland. A number of multivariate numerical techniques were employed to glean information from the collected data, including cluster analysis and canonical community ordinations. Variance partitioning was used to decompose the total variation in the diatom data into components representing within-lake, catchment and geographical attributes. Altogether 167 diatom taxa, belonging to 27 genera, were identified from the epilithic habitats. Tabellaria flocculosa was the most common and widely distributed taxon, occuring in all 41 lakes, followed by Nitzschia perminuta, Brachysira vitrea, Achnanthes minutissima and Brachysira brebissonii. Cymbella microcephala had the highest relative abundance (55.2 %) of any diatom in one single lake. Cluster analysis did not aggregate the lakes of the two subregions into two separate groups. Instead, spatial variability and diatom assemblage structure seemed to be controlled by local limnological factors. The most dominant ecological gradient comprised chemical variables, such as conductivity, pH and alkalinity. Catchment and location parameters, such as bedrock characteristics, distance to western seaboard and precipitation also contributed significantly to the variance in taxonomic composition. Results of variance partitioning showed that proximal within-lake variables explained the overwhelming majority (20.6 %) of the variance in the epilithic diatom data. Variables belonging to catchment and location categories seemed to be less important, each of them accounting for only half of the amount explained by the within-lake variables.