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Format:
Print
Author:
Koff, Andrew T.
Dept./Program:
Geology
Year:
2012
Degree:
MS
Abstract:
This project applies multi-proxy analysis of two sediment cores from the US portion of Missisquoi Bay (MB) to make interpretations about environmental changes within the bay and surrounding watershed during the last 9,000 years. Located at the end of the Northeast Arm of Lake Champlain, MB is a large, shallow, well-mixed embayment (mean depth =2.8m, surface area =77.5 km²) that has recently experienced an increase in external nutrient loading, leading to a state of eutrophication.
Core samples were analyzed for %Corg, %N, C/N, biogenic silica, water content, grain size and magnetic susceptibility in order to make interpretations about the amount, type and distribution of organic and inorganic matter in the MB sediment record. This study identified four distinct intervals representing deposition periods with different geochemical characteristics: the bottom portion of the core, designated Period 4, is characterized by elevated levels of organic matter and was deposited between ~9,000 to 8,000 cal years BP; Period 3 (~8,000 to 1,900 cal years BP) by stable but low organic matter levels; Period 2 by increasing levels oforganic matter from ~1,900 cal years BP to the calendar year 1900 AD; and Period 1 (1900 to today), by the maximum levels of organic matter recorded over the core profiles.
The older period of high productivity (Period 4) was statistically less intense and from the modern period brought on by anthropogenic nutrient inputs (Period 1). Lower lake level along with warm and dry conditions during Period 4 enabled the growth of additional aquatic plants within the bay. This period ended abruptly and was followed by low levels of %C, indicative of colder and wetter conditions related to the 8200 year BP climate event. Variation in the sediment record at 5500 and 400 years BP also can be attributed to known Holocene climate events. A better understanding of the past lake environment may be useful in understanding the current hypereutrophication of Missisquoi Bay, and predicting the bay's response to 21st century climate change.