A paleolimnological record of anthropogenic impact on water quality in First Lake, Lower Sackville, Nova Scotia
LE3 .A278 2013
Bachelor of Science
Environmental & Sustainability Studies
Lakes situated in urban environments are commonly subjected to a variety of anthropogenically induced pressures. Since 1920, First Lake in Lower Sackville has been the focus of watershed development and lake water quality degradation is an ongoing concern. A paleolimnological approach was undertaken to provide insight into the relationship between watershed development and water quality. A year-long study of limnological conditions in the lake and a historical survey of existing data were conducted to characterize seasonal physical and chemical lake conditions. First Lake stratifies strongly during the summer and algal blooms and hypolimnic anoxia commonly occur. Survey results indicate that shallow Secchi disk depths (< 2 m), strong stratification (~6 m), neutral pH values, and oxygen-deprived bottom waters (<5%) commonly develop as the summer progresses. A 33 cm long sediment core from the lake basin captured approximately 600 years of sediment accumulation. Atmospheric Pb concentrations were used to approximate sedimentation rates. Pre-development (pre-1920) data indicate a productive, likely mesotrophic lake. Higher δ 15N values and lower C/N ratios near the top of the core indicate increased primary productivity within the lake as a result of increased nutrient input from early agricultural development after 1920. Changes in concentrations of Ti, Cu, K, loss-on-ignition and magnetic susceptibility values indicate landscape instability, and an increase in sediment and toxin transfer into the lake associated with urbanization in 1960. These data indicate that changes in water quality in First Lake are strongly linked to specific anthropogenic activities in the watershed, an understanding of which is a fundamental factor in developing effective lake management strategies.
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