47 Records of Environmental Change from Lacustrine Archives (Posters)

Tuesday, 22 March 2016
1:30 PM - 5:30 PM
Convention Hall

RECONSTRUCTING PAST PRIMARY PRODUCTIVITY OF FOUR NEW YORK FINGER LAKES USING MULTIPLE PROXIES

Paper number: 47-20
Program: Theme Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

Eutrophication is one of the most pressing water quality issues in freshwater systems worldwide. Sediment cores provide a valuable means of reconstructing changes in lake trophic state because when dated using 137Cs and 210Pb, they permit inferring the factors involved in eutrophication at a high temporal resolution. Box cores were collectedand analyzed from four New York Finger Lakes (Conesus, Honeoye, Canandaigua, Cayuga) to reconstruct shifts in the trophic status over the last century using several paleo-productivity proxies. These lakes were chosen because they currently reflect a wide range of trophic states, mixis types, morphological conditions, and land use in their respective watersheds. The principal objective of this study is to evaluate the use of the stable carbon (δ13C) and nitrogen (δ15N) isotopic composition of bulk organic matter to infer paleoproductivity across the trophic gradient of these freshwater lakes by analyzing modern sediments and assessing stratigraphic changes in the cores.

The atomic C/N ratios and Suess-corrected δ13C indicate that sedimented organic matter is algal in origin. In all lakes, the wt.% organic carbon and nitrogen gradually increased since the early 1900s. The δ15N also increased upcore in the three lakes in agriculturally-dominated watersheds. The δ15N in Honeoye was lower than the other lakes and remained constant because it is a shallow, polymictic lake in a forest-dominated watershed. The δ13C gradually declined in all lakes during the 1940-1990s before increasing again upcore. This trend is muted in Honeoye because of the influence of Hurricane Agnes (1972). Increased nutrient loading and primary productivity likely explains the trend in δ13C. Although δ13C values typically increase with increasing biological productivity as more 12C is removed during photosynthesis, δ13C values may become more negative if primary producers are dominated by chemoautotrophic or methanotrophic microbes, typical of eutrophic-hypereutrophic lakes. When plotted against each other, the δ13C and δ15N of sediment from each lake show good separation in isotope space. The δ13C and δ15N was lowest in the most productive lakes and highest in the least productive lakes.

Geological Society of America Abstracts with Programs. Vol. 48, No. 1

doi: 10.1130/abs/2016NE-272084

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