Surface-water Acidification and Reproducibility of Sediment Cores from Kejimkujik Lake, Nova Scotia, Canada

摘要

A total of nine sediment cores were collected from the five deep basins of Kejimkujik Lake, located in southwestern Nova Scotia, Canada, in order to track changes related to surface-water acidification and to test reproducibility of results between sediment cores from different basins in a large lake. Present-day and pre-industrial (c. 1850) samples were analyzed from all cores and detailed diatom profiles were undertaken on three cores to determine the timing of acidification. All three detailed diatom profiles show declines in inferred pH starting in the early 1930-1940s. Since the 1940s, diatom-inferred lakewater pH has declined from a background pH of ～5.8 (± 0.4) to a current diatom-inferred pH of ～4.9 (± 0.1). This corresponds to the current (2001-2002) range of measured lakewater pH =4.7—5.2 with a mean pH=4.9. Species diversity of diatoms also declines markedly in all cores with the Hill's N2 index decreasing from ～5 to near 1. The pre-impact diatom assemblages were dominated by Aulacoseira spp. and have since changed to dominance by Asterionella ralfsii var. americana ( > 45 μm). All nine sediment cores showed similar changes in diatom assemblages, diatom-inferred pH, and timing of the onset of acidification. Thus, paleolimnological inferences from deepwater sediment cores were highly reproducible in this large, morphometrically complex lake system.