Publication Date

April 2018

Advisor(s)

Timothy Ku

Major

Earth & Environmental Sciences

Language

English (United States)

Abstract

Cultural eutrophication is a major problem affecting lakes throughout North America. This multi-proxy study on lake productivity at Lake Wononscopomuc, Connecticut, documents cultural eutrophication from pre-European settlement to modern day, and examines the effectiveness of its recent lake remediation practices. Lake Wononscopomuc is one of the only marl lakes in Connecticut, providing a unique opportunity to study the relationship between eutrophication and sediment carbonate concentrations. This study analyzed productivity using water chemistry, and sediment organic carbon and calcium carbonate wt.%, organic carbon/nitrogen, d13Corg, d13CCaCO3, and ?d 13C (d13CCaCO3-d13Corg). Two sites, one from the deepest point of the lake (30 m) and one from a shallower point (7.5 m), were examined in detail, with the core from the deeper site reaching a maximum age of approximately 1400 A.D. Sediment ages were calculated based on mercury and radiocarbon analysis. Large differences in carbonate concentrations were observed across the cores at different depths, with very low concentrations (<5%) at the deep site and high concentrations at the shallower site (40-70%), which may be due to greater carbonate dissolution at the deeper site. The sediment record was divided into three major time zones: the pre-European (1400-1700 A.D.), the industrial (1700-1900 A.D.), and the modern (1900-2017 A.D.). Organic carbon mass accumulation rates, d13Corg, and d13CCaCO3 increased when productivity increased with the introduction of the iron industry, but after the industry?s collapse in the area, there was a recovery period. A similar trend is evident in the modern period, with peak cultural eutrophication in 1950 to 1980 and a recovery period, likely due to remediation practices. However, leading up to modern day from the industrial period d13Corg and d13CCaCO3 display an inverse relationship, where d13CCaCO3 decreases while d13Corg increases. This relationship is not solely due to productivity changes, and may be due to changes in the sources of calcium carbonate or the effects of other aquatic vegetation. Based on decreasing organic carbon mass accumulation rates and decreasing d13Corg, recent management practices on the lake have been successful in curbing some of the eutrophication effects, but more must be done to limit the extent and duration of anoxic conditions in the bottom waters. Additionally, future management practices must take into consideration the potential impact of climate change and warming temperatures. Multiproxy studies like these can provide insight into productivity changes and assess lake remediation efforts in marl lakes affected by cultural eutrophication.

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