PERIPHYTIC DIATOM ASSEMBLAGES FROM HIGH ARCTIC PONDS

Epiphytic, epilithic, and surface sediment diatom assemblages were ide ntified and enumerated from 35 study ponds on Cape Herschel (78 degree s 37'N, 74 degrees 42'W), east-central Ellesmere Island, Canada. All t he sites are shallow (maximum depth < 2 m), clear, oligotrophic, and f reshwater. The ponds freeze completely for 10 months of the gear. Majo r ion concentrations are relatively similar among the 35 sites, althou gh environmental gradients exist. Over 130 diatom taxa from 28 genera were identified in the periphyton samples. Marked differences in speci es composition were evident among the ponds. Moreover, many of the dia toms exhibited varying degrees of microhabitat specificity. Variance p artitioning by canonical correspondence analysis showed that 26% of th e total variance exhibited by diatom species composition could be acco unted for by the measured environmental variables( i.e. 10.2% by habit at and 15.8% by water chemistry). Pondwater alkalinity best explained the distribution of taxa, and weighted averaging regression and calibr ation were used to develop a transfer function to infer pondwater alka linity from the diatom assemblages. Other important environmental vari ables included [Na+] for the epilithic and [SiO2] for the epiphytic as semblages.