HR: 1340h
AN: H53A-1221    [Abstracts]
TI: Modern Limnological and Contamination Records from a Drinking Water Lake in Central New York
AU: * Bookman, R
EM: rbookman@syr.edu
AF: Syracuse University, Department of Earth Sciences, 204 Heroy Geology Lab, Syracuse, NY 13244 United States
AU: Seltzer, G
EM: goseltze@syr.edu
AF: Syracuse University, Department of Earth Sciences, 204 Heroy Geology Lab, Syracuse, NY 13244 United States
AU: Driscoll, C
EM: ctdrisco@mailbox.syr.edu
AF: Syracuse University, Civil and Environmental Engineering, 220 Hinds Hall, Syracuse, NY 13244 United States
AU: Montesdeoca, M
EM: mmontesd@ecs.syr.edu
AF: Syracuse University, Civil and Environmental Engineering, 220 Hinds Hall, Syracuse, NY 13244 United States
AU: Philippon, J
EM: jphilipp@syr.edu
AF: Syracuse University, Department of Earth Sciences, 204 Heroy Geology Lab, Syracuse, NY 13244 United States
AB: Otisco Lake is the easternmost of the Finger Lakes in central New York. It is a mesotrophic lake with a maximum depth of 20 m and a drainage area of 94 km$^{2}$. Since the beginning of the 20$^{th}$ century the lake waters have been used for drinking water supply. Using a gravity corer we collected four sediment cores with a maximum length of 45 cm from the bottom of the lake. The cores represent the last $\sim$150 years. The changes with depth in nitrogen, carbon, and the trace metal mercury were recorded by analyzing 1 to 2 cm long segments from each core. The chronology was obtained on one of the cores using the Lead-210 dating method and by identifying the rise in copper concentration as a marker horizon of the year 1942, when copper sulfate was first added to the lake to control algal blooms. Lead-210 was measured by $\alpha$-spectrometry and dates were calculated according to the CRS model. The sediment accumulation rates calculated from the unsupported lead activity show an increase from 0.06 g cm$^{-2}$yr$^{-1}$ at the bottom of the core to 0.15 g cm$^{-2}$yr$^{-1}$ at depth of 13 cm. In the upper part of the core the sediment accumulation fluctuates between 0.10 and 0.13 g cm$^{-2}$yr$^{-1}$, with the lowest value at the uppermost cm in the core. Background copper concentrations average 25 ug g$^{-1}$ in the lower 20 cm of the core, but from depth of 22 cm to 13 cm the concentrations rapidly increase up to 142 ug g$^{-1}$. Concentrations along the rest of the upper core fluctuate around 112 ug g$^{-1}$. The beginning of increased concentration correlates well with the Lead-210 chronology marking the 1942-year horizon. Mercury contamination in lakes is largely attributed to atmospheric deposition of pollutant emissions. Total mercury at Otisco Lake was measured in the four cores showed almost identical profiles. Mercury flux increased from around 50 ug m$^{-2}$yr$^{-1}$ in the 1870's to a maximum value of 132 ug m$^{-2}$yr$^{-1}$ during the mid 1970's, with a steep increase beginning at the 1940's. At the beginning of the 1980's the mercury flux decreased to ~90 ug m$^{-2}$yr$^{-1}$, but rose again in the 1990's. The top 2 cm dated to the last decade show a significant decrease in concentration to values around 80 ug m$^{-2}$yr$^{-1}$. Carbon and nitrogen fluxes mimic the trends of mercury, although their concentrations peak a decade later. Fluxes start to rise in the 1940's from an average of 2.3 and 0.25 mg cm$^{-2}$yr$^{-1}$, respectively, and reach their peak values (8 and 0.66 mg cm$^{-2}$yr$^{-1}$, respectively) during the 1980's. As with mercury, the nutrient flux in the top 2 cm of the record shows decreasing values. The mercury fluxes in the sediments represent increased atmospheric pollution from industrial activities that reached their maximum values before pollution problems were addressed seriously with the 1970 Clean Air Act. The passage of the 1990 Clean Air Act amendments that strengthen enforcement provisions may be the cause for the decreasing trends in the last decade. The lake waters are likely contaminated mainly by atmospheric pollution. However, since there is a good correlation between the sediment accumulation rate, mercury flux, and nutrients fluxes, we believe that land-use changes have a major influence on the lake and sediment chemistry. This study may assist in policy making and management of Otisco Lake and its watershed, as well as similar water bodies that are used as drinking water supplies.
DE: 4239 Limnology
DE: 1845 Limnology
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting