RECONSTRUCTION OF POST-GLACIAL MASS ACCUMULATION RATES FROM A SMALL KETTLE LAKE, SOUTHERN ONTARIO, CANADA

Environmental changes impacting lakes and their catchments are commonly recorded as changes in the accumulation rates of the organic, carbonate, and siliciclastic sediment fractions. Such reconstructions are not very common in the lower Great Lakes region of North America but are important because they offer a long-term record of sensitivity and response to perturbations that may be relevant to future environmental changes. We report results from Barry Lake, which is a small kettle lake in south-central Ontario. Mass accumulation rates for three cores spanning the last 13,000 years are presented that represent the lake’s off-shore, near-shore, and marsh environments. These cores show basin-wide trends as well as trends that differ between the lake and marsh environments. Organic mass accumulation rates, which represent productivity, are low (< 12 mg/cm²/yr) throughout the post-glacial period, particularly under lacustrine conditions. However, increases in productivity are evident in all three cores following European colonization. Carbonate accumulation rates fluctuate considerably within the cores and primarily represent changes in water depth. Shallow conditions produce the greatest carbonate amounts, which decrease from the marsh-core (30 mg/cm²/yr) lakewards to the off-shore environment (2 mg/cm²/yr). High-water conditions produce carbonate amounts up to two orders of magnitude lower in the lake cores due to dissolution in hypoxic waters. Secondary controls on accumulation rates include changes in productivity and detrital carbonate inputs. Siliciclastic inputs from the surrounding catchment are high during the first 3,000 years following deglaciation (~30 mg/cm²/yr) before reaching a post-glacial equilibrium of 0.2-1 mg/cm²/yr by 10,000 cal BP. European land clearance is evident in all three cores, though the magnitude of change decreases distally from the hillslopes due to the filtering effect of the marsh. The marsh core has a mass accumulation rate of 100 mg/cm²/yr while the lake cores have rates more than an order of magnitude less. The results demonstrate the influence of core location on accumulation rates and that not all locations will agree with each other due to variations in sensitivities to external forces and environmental conditions.