CHIRONOMIDAE (DIPTERA) - QUANTITATIVE PALEOSALINITY INDICATORS FOR LAKES OF WESTERN CANADA

A survey of chironomid remains preserved in the surficial sediments of 86 British Columbia lakes was conducted to assess the feasibility of reconstructing palaeosalinities from assemblages of fossil chironomid head capsules. Many taxa common in freshwater lakes were either rare o r absent at higher salinities. Lakes having salinities greater than ab out 10.0 g . L(-1) were distinguished by the overwhelming relative abu ndance of Cricotopus/Orthocladius. In less saline waters, common taxa included Chironomus, Procladius, Psectrocladius, and the subtribe Tany tarsina. Heterotrissocladius, Lauterborniella/Zavreliella, Pagastiella , and Sergentia were: only collected in freshwater habitats. Canonical correspondence analysis revealed that three environmental variables ( late summer lakewater salinity and concentrations of Sr and total P) e xplained significant variation in the weighted averages of taxa. Tanyt arsina and Dicrotendipes were common at low Sr concentrations in carbo nate lakes. A weighted-averaging calibration function was developed to infer salinity on the basis of fossil fauna. This model will allow pa laeolimnologists to detect transitions between freshwater and moderate ly saline states and can be used to assist palaeoclimatic reconstructi ons for athalassic lake sites.