| Wetland and upland vegetation changes over a period of 8300 years, and sedimentary δ13C, δ15N, and C:N changes from the past 10,500 years were examined in a St. Lawrence River coastal wetland. Evidence of a highstand, the Nipissing Flood, was found between 5200 and 4500 YBP, indicated by a +8‰ shift in sediment δ 13C, a persistent anomaly in the sediment organic matter, and a period of depressed C:N ratios. Climate cycles, 3300 years in duration, were inferred from >50% shifts in Poaceae (grass) pollen relative abundance. An 80% increase in relative abundance of Typha (cattail) pollen abruptly occurred around 1894 A.D., following European settlement and concurrent with peak agricultural land-clearing, and was probably associated with increased upland erosion. Ultimately, changes in water depth resulting from a combination of isostatic uplift, vertical accretion of the substrate, and climate change regulate the long-term succession of the wetland. |
