Seasonal changes in phytoplankton community structure in relation to physico-chemical factors in Loch Lomond, Scotland

An intensive seasonal sampling programme at two contrasting sites in Loch Lomond, the largest lake in Britain, showed the 1992-93 status of the loch to be mesotrophic in the shallow south basin and oligotrophic in the deeper north basin. There is evidence for an increase in both phytoplankton production and reactive phosphorus concentrations in the loch during the two decades up to 1993. Canonical Correspondence Analysis (CCA), plus classification (by Two-Way Indicator Species Analysis: TWINSPAN) of the dataset of time-position samples from the loch revealed that seasonal factors (particularly the thermal regime of the loch, and associated variables) remain more important than non-seasonal environmental variables in predicting changes in phytoplankton community composition. As in the 1970s, the community remains dominated by a diatom-desmid assemblage, but cyanobacteria blooms, albeit at fairly low abundance, are becoming a frequent phenomenon in the south basin of the loch.