Epiphytic, epilithic, and surface sediment diatom assemblages were identified and enumerated from a suite of 35 study ponds from Cape Herschel (78°37'N, 74°42'W), east-central Ellesmere Island. Physical and chemical limnological data indicate that all the sites are shallow (maximum depth, Zmax <2 m), clear, oligotrophic and freshwater. The ponds are completely frozen for 10 months of the year; however, during the short summers, water temperatures warm substantially (to a recorded maximum of 17°C) and fluctuate diurnally. With the exception of one pond (Paradise Pond, pH = 6.5), the ponds are alkaline (pH range of 7.4 to 8.60), reflecting local geology (e.g., calcareous tills). Major ions in water are relatively similar amongst the 35 sites, although environmental gradients exist.

Over 130 taxa from 28 genera were identified in the periphyton samples. Although some of the recorded taxa were common to all three habitats, many of the diatom taxa exhibited varying degrees of microhabitat specificity. Marked differences in species composition are evident amongst the ponds. Variance partitioning by CCA (Canonical Correspondence Analysis) showed that 26% of the total variance exhibited by diatom assemblages could be explained by the measured environmental variables (i.e., 10.2% by habitat and 15.8% by water chemistry). Further analyses of individual microhabitat assemblages identified alkalinity as the common environmental variable explaining a significant portion of the diatom data variance. Other important environmental variables were: [Na] and the percentage of moss and sediment within the pond for epilithic assemblages; and [SiO2] for epiphytic assemblages. A DCA ordination of the three assemblages showed that sediment assemblages represented reasonable integrators of the various microhabitats, thereby reconfirming their usefulness for paleolimnological interpretations. Weighted averaging and calibration were used to develop a transfer function to infer pondwater alkalinity. Optima derived from rock and sediment assemblages were more reliable than those derived from moss assemblages.

Paleolimnological analyses from seven ponds showed that sediment cores from these shallow sites do appear to faithfully record a useful stratigraphic record of environmental change. The ponds' sediments span time frames ranging from about 9,000 years to a few centuries, depending on their proximity to the sea and the pattern of isostatic emergence. Striking successional changes were noted in diatom assemblages during the ponds' recent (ca. last 200 year) histories. In most sites, a long-lasting (several thousand year) and relatively stable benthic Fragilaria pinnata/construens assemblage was replaced by a diverse assemblage of benthic diatom taxa (e.g., Achnanthes spp., Nitzschia spp., Cymbella spp, Pinnularia balfouriana). Diatoms that apparently thrived on Cape Herschel a century or two ago (e.g., Epithemia sorex, Fragilaria pinnata/ construens complex etc.) no longer live on the Cape, further suggesting that this region has experienced recent environmental changes. Although the causes of these diatom assemblage shifts cannot be determined at this time, regional environmental changes likely related to anthropogenic activity may be responsible.