Modern diatom assemblages in Central Mexico: the role of water chemistry and other environmental factors as indicated by TWINSPAN and DECORANA

SUMMARY. 1. Modern diatom samples, for which physical and chemical environmental conditions were recorded, were collected from forty‐seven sites across Central Mexico 2. The results of the diatom counts were analysed using the clustering program TWINSPAN and the ordination program DECORANA. 3. Results from ‘Laguna Zacapu and associated sites’ showed that where water chemistry varies little between sample sites the effects of habitat are emphasized. This data set highlighted the problems of looking for modern analogues where anthropogenic disturbance is great. 4. TWINSPAN results from the ‘Other Sites’ data set suggested possible changes in diatom assemblages with chemical composition. The DECORANA analyses, however, again seemed to emphasize habitat. 5. In the context of this study, bottom sediment samples appeared to provide the most useful picture of ‘average’ conditions and to be the best source of analogues for the interpretation of fossil assemblages.