Niagara Power Project FERC No. 2216
DETERMINE
IF WATER LEVEL FLUCTUATIONS IN LEWISTON
RESERVOIR
INCREASE MERCURY THAT IS BIOAVAILABLE
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Prepared for: New York Power Authority
Prepared by: Tetra Tech, Inc.
August 2005
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Copyright © 2005 New York Power Authority
anoxic without oxygen or deoxygenated
cfs cubic feet per second
cm centimeter
DO dissolved oxygen
DOC Dissolved Organic Carbon
Hg(0) elemental mercury
Hg(II) mercury II or ionic mercury
hypolimnia the lower portion of the lake water column
L liter
Littoral the shallow portion of the lake
LPGP Lewiston Pump Generating Plant
M mega (prefix for one million)
m meter
MeHg methylmercury
ml milliliter
mm millimeter
MW megawatt
NPP Niagara Power Project
NYSDEC New York State Department of Environmental Conservation
NYSDOH New York State Department of Health
oxic oxygenated
ppb parts per billion
ppm parts per million
Profundal the deepwater portion of the lake
RMNPP Robert Moses Niagara Power Plant
μ micro (prefix for one-millionth)
The New York Power Authority (NYPA) is engaged in the relicensing of the Niagara Power Project in Lewiston, Niagara County, New York. The present operating license of the plant expires in August 2007. As part of its preparation for the relicensing of the Niagara Project, NYPA is developing information related to the ecological, engineering, recreational, cultural, and socioeconomic aspects of the project.
One of the major components of the Niagara Power Project is the 22-billion-gallon Lewiston Reservoir, which was built in the late 1950s and serves as a pumped storage reservoir for the Power Project. Operation of the Niagara Power Project can result in water level fluctuations in the Lewiston Reservoir of 8-18 feet per day, and as much as 36 feet per week. Concerns have been raised regarding the influence of changing water levels, or drawdown, on the mercury concentrations found in the water and biota of the reservoir. One of the unique features of Lewiston Reservoir is that up to 93% of the water in the reservoir is exchanged on a weekly basis. This rapid exchange of water mitigates against the formation and accumulation of bioavailable mercury. Methylmercury is the form of mercury that is bioavailable, and the formation of methylmercury is called methylation. Unfortunately, most of the research performed to-date on mercury in reservoirs has involved systems with physical, flow, and drawdown characteristics very different from those in Lewiston Reservoir. However, much of the research on the effects of water level fluctuations on methylation is still relevant to Lewiston, despite the much more frequent and extensive drawdown characteristics of the Lewiston Reservoir. In addition, some previous research results are presented to provide background information on why concerns have been presented with regard to mercury in Lewiston Reservoir.
Data exist for multiple sites in North America and Europe
that show a clear increase in the concentration of mercury in fish due to
reservoir creation. Elevated
concentrations of mercury in fish have also been reported downstream of some
hydroelectric developments. The increase
in the concentration of mercury in fish in reservoirs is time dependent, first
rising after reservoir creation and then declining over time. The magnitude and duration of the observed
increases appear to depend on fish species and local conditions. Typically the concentrations of mercury in
fish have been reported to increase and then return to background
concentrations within 10-30 years.
Drawdown has been discussed in the literature as a possible mechanism to influence the concentration of mercury in fish, both positively and negatively, when considering older reservoirs. These studies have presented several possible mechanisms relating water level fluctuations to mercury bioaccumulation in reservoirs, but significant gaps in our understanding of the relevant processes still exist. Unfortunately, most of the literature involves reservoirs that are drawn down once or twice per year, whereas Lewiston Reservoir is drawn down on a weekly basis. To our knowledge, there are no studies that have specifically investigated the effects of drawdowns on mercury bioaccumulation in pump-storage reservoirs.
These factors relating mercury bioaccumulation to reservoir drawdown have been evaluated with respect to the unique characteristics of Lewiston Reservoir. Some of the key characteristics of Lewiston Reservoir that mitigate against the formation and accumulation of methylmercury include short hydraulic residence time, low organic content of the sediments of the drawdown zone (riprap shoreline area), high pH and high di