FRESH-WATER DIATOMS FROM HIGH ARCTIC PONDS (CAPE HERSCHEL, ELLESMERE-ISLAND, NWT)

A taxonomic and preliminary ecological description is provided for dia tom assemblages identified from the surficial sediments of 36 ponds fr om Cape Herschel (78-degrees 37'N, 74-degrees 42'W), on the east-centr al coast of Ellesmere Island. Physical and chemical limnological data indicate that, with few exceptions, the ponds are shallow, clear, olig otrophic, alkaline, and non-saline. A total of over 122 diatom taxa fr om 27 genera were identified, some of which are as yet undescribed. Be nthic diatoms are abundant, whereas planktonic taxa are absent. Overal l species richness on the Cape is high, but is low within each pond. S triking differences in species composition are evident amongst the pon ds. A CCA (Canonical Correspondence Analysis) ordination indicated tha t Ca2+ and pH were the environmental variables most significant to the diatom flora but only accounted for 11.4% of the floristic variation. It is likely that benthic diatoms closely reflect substrate compositi on (e.g., rock, moss, sediment), rather than simply water chemistry. I n addition, other factors, such as herbivory, are likely important in determining diatom species composition.