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

An intensive seasonal sampling programme at twocontrasting sites in Loch Lomond, the largest lake inBritain, showed the 1992–93 status of the loch to bemesotrophic in the shallow south basin andoligotrophic in the deeper north basin. There isevidence for an increase in both phytoplanktonproduction and reactive phosphorus concentrations inthe loch during the two decades up to 1993. CanonicalCorrespondence Analysis (CCA), plus classification (by Two-Way Indicator Species Analysis: TWINSPAN) ofthe dataset of time-position samples from the lochrevealed that seasonal factors (particularly thethermal regime of the loch, and associated variables)remain more important than non-seasonal environmentalvariables in predicting changes in phytoplanktoncommunity composition. As in the 1970s, the communityremains dominated by a diatom-desmid assemblage, but cyanobacteria blooms, albeit at fairly low abundance,are becoming a frequent phenomenon in the south basinof the loch.