A Diatom-based Paleohydrological Model for the Mackenzie Delta, Northwest Territories, Canada

Abstract

Floodplain lakes are tightly coupled to their associated river systems and their sediment records should provide integrative records of this interaction. Surface sediments and selected limnological variables were collected from 77 Mackenzie Delta lakes representing three categories of river influence: lakes having continuous connection with the Mackenzie River (n = 23; no-closure), lakes that flood every spring but lose connection during the summer (n = 26; low-closure), and lakes that flood only during an extreme spring flood stage (n = 28; high-closure). Summer lake production, using winter methane concentration as a proxy, and river influence were identified as the principal limnological gradients separating delta lakes. This river influence/primary production gradient also accounted for the greatest amount of variation within the surface sediment diatom assemblages. The diatom flora of the Mackenzie Delta lakes was dominated by benthic taxa, particularly the genera Nitzschia and Navicula, with a greater abundance of stalked, epiphytic taxa in the high-closure lakes. A robust predictive model was developed for inferring lake production from fossil diatom assemblages. The model provides a tool for estimating long-term changes in river influence and lake dynamics from the sediment record of Mackenzie Delta lakes. Diatom-inferred river influence changes within these records may then be linked with past river discharge variability.