Cayuga Lake, the second largest of New York's Finger Lakes, is situated in a steep-sided, glacially carved valley in Central New York (refer to Figure 1.1-1). Morphometric characteristics of the lake, such as size, shape, and water volume, are summarized in Table 2.3.1-1. The lake is long and narrow, extending 61.4 km (38 mi) north from Ithaca to the lake's outflow into the Seneca River. With a maximum depth of 132.6 m (435 ft) and a mean depth of 54.5 m (179 ft), Cayuga Lake has a large volume of deep water (referred to as the hypolimnion) that remains cold year round. It is this feature of Cayuga Lake that makes Lake Source Cooling at Cornell feasible.
Much of the environmental impact analysis for LSC is focused on southern lake basin, defined as the region south of Myers Point. The proposed LSC intake and outfall are located in this region of the lake, and any thermal, chemical, and/or biological impacts of LSC construction and operation are likely to be most apparent there.
2.3.1.1 Classification and Designated Use.
Pursuant to Article 17 of the Environmental Conservation Law, the NYSDEC has promulgated best usage classifications and ambient water quality standards for the state's surface waters. The best usage classifications specify which types of human uses, such as drinking, swimming, and fishing, are appropriate within a given portion of a water body. The determination of "best use" is based on variables such as existing water quality, flows, and current and projected uses of the water body and its watershed. Ambient water quality standards are legally enforceable limits on certain factors that can affect water quality, such as chemicals and bacteria. These standards are adopted to protect the water body's designated best use.
Portions of Cayuga Lake are classified AA, A, and B (Figure 2.3.1-1). Class AA is the highest classification of surface waters in New York, and reflects a best usage for water supply without filtration. The best usage of Class A waters is for water supply after coagulation, sedimentation, and filtration. The best usage of Class B waters is for water contact recreation. The water quality standards that protect these uses are also protective of fish survival and propagation. Table 2.3.1-2 summarizes these best usage classifications.
Note that all of Cayuga Lake's water segments, with the exception of the most southern, are required to meet water quality standards protective of salmonid fish as designated by the (T) notation shown in Figure 2.3.1-1. More stringent standards for dissolved oxygen and ammonia N are in place in (T) waters.
2.3.1.2 Human Uses of Cayuga Lake, Public and Private.
Cayuga Lake is used for municipal and private water supply, water-based recreation, agricultural water supply, waste disposal, and noncontact cooling water. There are five state parks on the lake, including the Allen H. Treman State Marine Park. Wetlands at the lake's northern outlet are managed by the U.S. Fish and Wildlife Service as the Montezuma National Wildlife refuge. New York State also maintains a wildlife management area near the outflow of Cayuga Lake to the Seneca River. Numerous private marinas, yacht clubs, and sailing clubs are located along the lake shoreline.
The lake's recreational fishery for salmonids, particularly Atlantic salmon and lake trout, represents an important economic benefit. The NYSDEC strategic fishery management plan projected 480,000 angler trips in 1995, which would generate $10.8 million (Chiotti 1980).
There are currently five permitted direct dischargers to Cayuga Lake (Table 2.3.1-3). Of these five, three dischargers are municipal and two are industrial. LSC would represent a second permitted discharger of noncontact cooling water.
Several villages (Aurora, Union Springs, and Seneca Falls) use Cayuga Lake as a public water supply. Bolton Point water treatment plant in Tompkins County is currently permitted to withdraw up to 4.5 million gallons of water a day to serve several communities in the southeastern portion of the watershed (the Town of Ithaca, Town and Village of Lansing, Village of Cayuga Heights, and a portion of the Town of Dryden). The Bolton Point distribution system is interconnected to provide backup supply to the City of Ithaca and Cornell University. The City of Ithaca uses the lake tributary Six-Mile Creek as a primary supply; Cornell University draws its water supply from the lake tributary Fall Creek. Many individual homeowners draw water from the lake as well.
2.3.1.3 Watershed Characteristics.
2.3.1.3.1 Description of the Cayuga Lake Watershed.
The Cayuga Lake watershed encompasses lands within Seneca, Cayuga, and Tompkins counties (Figure 2.3.1-2). The watershed boundary is delineated by land areas that drain water directly into the lake, or into the tributaries that flow into the lake. The watershed area totals 4,051 km2 (1620 mi2), including the lake surface area of 173 km2 (69 mi2). Of the total watershed area, approximately half (1860 km2, 744 mi2) drains directly into the lake. The other half (2,018 km2, 807 mi2) is comprised of the land area that drains to the Seneca River, including the Keuka and Seneca Lake watersheds (Likens 1974). The Seneca River flows into the lake near the northern end, and flows out again at the lake's outlet (its northernmost point).Land uses within the watershed are primarily agricultural, residential, and forest. Data on the present land uses within the watershed were gathered from Seneca, Tompkins, and Cayuga counties and combined for presentation in Table 2.3.1-4. These data were compiled primarily in the 1980s, with more recent input from the Cayuga County portion of the watershed.
The land-use data presented in Table 2.3.1-4 were generated by each county in a slightly different manner, and were normalized by groupings into five major land-use categories: (1) residential; (2) commercial/industrial/vacant; (3) forest/recreational/wetland; (4) agricultural; and (5) educational/institutional.
The Seneca County Office of Real Property Services obtained its land classification data from the New York State Real Property Services (RPS) database. These data were originally provided in the format of the state land classification system used by the State of New York, and were subsequently aggregated into the five categories by the Seneca County Department of Data Processing for presentation in Table 2.3.1-4.
It should be noted that Seneca County did not have the Cayuga Lake watershed boundary delineated prior to land-use data acquisition. The watershed boundary within Seneca County was estimated from town tax maps and a county map illustrating hydrography. In this manner, a reasonable estimate of the total acreage per land-use classification was obtained for Seneca County. Tompkins and Cayuga counties both maintain geographic information system files of land-use areas and the Cayuga Lake watershed boundary, and were able to provide more accurate figures. Table 2.3.1-4 should therefore be considered as an estimate of land-use percentages.
In 1971, Child, Oglesby, and Raymond presented a general land-use breakdown for the Cayuga Lake watershed. The study was based on aerial photographs. The authors defined the Cayuga Lake watershed boundary somewhat differently than was done by the three counties in their land-use evaluation (mid-1980s through present). The 1971 report included the land area north of Seneca Falls that drains into the very north end of Cayuga Lake (by the Lake's outlet) or into the Seneca River. The recent land-use compilation excluded this area. Hence, Child et al. compiled data for an area that was 11.9 percent larger than the area evaluated in the recent land-use survey.
A comparison of the 1971 land-use data to the recent values (Table 2.3.1-4) provides only an estimate of the changes in land use that have occurred within the watershed over the last two decades. The comparison is complicated by differences in definition of land uses. In order to compare the data sets, we categorized the 1971 data to resemble the recent data as closely as possible. The most significant differences are the exclusion by Child et al. of wetlands as a category (which is combined with forest/recreation in the recent land-use study), and their inclusion of transportation and public lands as distinct categories. Child et al. did not delineate educational and institutional land uses as separate categories.
Based on a comparison of the land-use data, we can make several statements regarding land- use trends within the Cayuga Lake watershed over the past two decades. First, the amount of land area categorized as residential has risen considerably. Second, commercial/industrial uses of land appear to have risen moderately. Third, forested areas appear to have decreased considerably. The decrease in forested lands is likely due to residential development.
It is unlikely that the decrease in forested land area is as extensive as indicated by the difference between the 1971 and present data sets in Table 2.3.1-4. The difference is probably due in part to different methods for defining this land use by the three counties. For instance, some inactive agricultural lands may have been categorized as primary growth forests during field surveys.
Consequently, we cannot draw quantitative conclusions regarding the changes in land use within the watershed. It is not surprising that we see an increase in residential land use. This growth falls in line with the general trend of suburban growth in the eastern U.S.2.3.1.3.2 Tributary Flows and Hydraulic Retention Time.
Likens (1974) reported that more than 140 streams discharge to Cayuga Lake. The streams entering the lake's southern basin are by far the largest; Cayuga Inlet and Fall Creek together drain 39.8 percent of the direct watershed area (Table 2.3.1-5) when the Seneca River's contribution is excluded. When the land area drained by the river is included, the southern lake tributary watersheds drain 18.3 percent of the total watershed area. There are more than 100 small streams, intermittent streams, and gullies in the long, narrow, steeply sloped watershed contributing directly to Cayuga Lake.The lake's overall hydrologic budget is generally consistent with the watershed area; streamflow is proportional to the size of the drainage basin. Some exceptions to this general pattern in the Cayuga Lake watershed were noted by Likens (1974), indicating regions where groundwater inflows could be significant.
The two large southern tributaries, Fall Creek and Cayuga Inlet, are gauged by the U.S. Geological Survey. Monthly flow statistics for these tributaries are summarized in Table 2.3.1-6. In an average hydrologic year, streamflows are lowest in August and September, and highest in March and April. Figure 2.3.1-3 demonstrates the annual pattern of stream flow in Fall Creek.
Likens (1974) calculated Cayuga Lake's hydrologic budget for the period between August 1970 to July 1971. Tributary runoff contributed 91 percent of the total input of 18.56 x 108 m3 (6.5 x 109 ft3); precipitation onto the lake surface contributed the remainder. Discharge through the outlet was measured at 16.85 x 108 m3 (5.9 x 1010 ft3), and the evaporation was estimated at 1.92 x 108 m3 (6.7 x 109 ft3), based on the difference between the inflow and outflow, plus change in lake level. Using these numbers, the discharge during the 1970 to 1971 period represented 18 percent of the lake's volume. The hydraulic retention time is therefore 5.1 years. It should be noted that precipitation in 1970 to 1971 was higher than average.
However, this calculation includes the inflow and outflow from the Seneca River, which enters Cayuga Lake close to the outlet. It is reasonable to assume that the river waters do not mix south throughout the 38-mile lake. If the Seneca River's inflows are excluded, the hydraulic retention time based on the 1970 to 1971 data set would be estimated at 7.4 years. Oglesby (1978) reported an average hydraulic retention time of 12.8 years, with a range of 8.1 to 24.1 years, based on 36 years of outflow measurements. These calculations excluded the Seneca River contribution.
2.3.1.4 Morphometric Characteristics and Biotic Habitat.
Cayuga Lake is a long, deep lake with a "v-shaped" bottom profile. General morphometric characteristics are summarized in Table 2.3.1-1. The lake's bathymetric map (Figure 2.3.1-4) depicts the steeply sloped sides and profundal zone, the deep portion of the lake where light does not reach the bottom.
Cayuga Lake experiences vertical variations in water temperature that cause the lake to stratify thermally during the warm months of the year. During the late fall, winter, and early spring, the temperature and density of Cayuga Lake water are relatively uniform throughout the water column. As the sun's energy increases in the spring, the upper waters of Cayuga Lake begin to warm. These warm upper waters (the epilimnion) are separated from the lower, colder waters (the hypolimnion) by a region of rapid temperature transition (the metalimnion, which includes the thermocline). This stratification prevents the upper and lower waters of the lake from mixing. The lake waters remain stratified until late fall, when the epilimnion deepens and effectively erodes the metalimnion until lake temperature is again uniform.
The large volume of deep water in Cayuga Lake is illustrated by data showing the vertical distribution of water volume in Cayuga Lake (Figure 2.3.1-5). A plane through the lake at a depth of 40 m (131.2 ft) would bisect the lake into two equal volumes (Birge and Juday 1912).
This aspect of the lake's morphometry directly affects its biotic habitat. The lake's large volume of cold, well-oxygenated water provides a superb habitat for a cold water fishery. The littoral zone, which provides suitable habitat for warm water fish, is limited to the northern and southern lake basins.
2.3.1.5 Water Chemistry, Nutrients, Trophic State, and Dissolved Oxygen.
As part of the field investigations in support of LSC, we monitored several water quality indicators (such as temperature, dissolved oxygen levels, and concentrations of certain chemicals) at the LSC intake and outfall locations and depths. Results of this monitoring program are summarized in Table 2.3.1-7. The complete set of water quality data collected during the 1994 to 1996 field investigations in support of LSC are provided as Appendix C-1.
One of the most significant characteristics of a lake is its status in the aging process, known as eutrophication. Lakes naturally evolve from a nutrient-poor (oligotrophic) state, with low levels of nutrients and biological productivity, to an intermediate state (mesotrophic), and eventually to a nutrient rich and highly biologically productive state (eutrophic). Biological productivity refers to the growth rate of aquatic organisms that are part of the lake ecosystem. Primary productivity is the growth of plants and algae (including cyanobacteria, commonly known as blue-green algae) in a lake, organisms at the base of the lake's food web. An increase in primary productivity in the lake will affect the biological productivity of the ecosystem. Secondary effects of eutrophication, such as depletion of dissolved oxygen in the hypolimnion, can diminish a lake's suitability for meeting designated uses.
The rate of eutrophication depends on the lake's morphometry, geologic setting, land use and vegetative cover within the watershed, and hydrologic regime. The process can be slow, with lakes existing in a trophic equilibrium for decades. Human activities within the watershed that increase the loading rate of nutrients can accelerate natural aging in a process known as cultural eutrophication.
Phosphorus is the nutrient that limits primary productivity in most northeastern lakes, and is the limiting nutrient in the Finger Lakes. A separate section of this environmental impact statement (Section 2.3.3) discusses the potential impacts of LSC on phosphorus loads, concentrations, and related water quality characteristics.
Cayuga Lake is currently mesotrophic, exhibiting characteristics of moderate productivity. It appears to be the most productive of the Finger Lakes, based on a trophic state index comprised of phosphorus, chlorophyll a (an indicator of the amount of algal life), and Secchi disk transparency (an indicator of water clarity) (Bloomfield 1978). Since eutrophication is a continual process, the divisions between oligotrophic, mesotrophic, and eutrophic are somewhat arbitrary. Carlson (1977) designed a trophic state index for lakes to help scale the degree of eutrophication. The index is valuable for tracking a lake's water quality over time, or for categorizing large numbers of lakes. Table 2.3.1-8 compares results of the 1994 to 1996 monitoring program to the trophic state index.
Nitrogen, another important macronutrient for plant growth, is present in abundant supply in Cayuga Lake. Nitrogen enters the lake from point sources, such as treated wastewater, and nonpoint sources, such as agricultural runoff and atmospheric deposition. In the aquatic environment, nitrogen (N) exists as nitrate, ammonia, organic nitrogen, or nitrite. Ammonia N is the form of nitrogen that is most available for algal growth. In unpolluted waters, ammonia N is typically present at low concentrations (less than 50 µg/l), nitrate N is less than one mg/l, and nitrite N is rarely detected.
Nitrate N concentrations in Cayuga Lake average approximately 1 mg/l, which is consistent with the historical data, but relatively high compared to other regional lakes. The southern lake basin has concentrations of ammonia N approximately 20 µg/l higher than background in the regions directly affected by the wastewater treatment plant effluent discharges. No exceedances of New York State ambient water quality standards for ammonia N (which vary as a function of pH and temperature) have been detected during the LSC field program.
Silica is another important nutrient for the growth of phytoplankton, particularly those plankton species classified as diatoms. This element is present in the form of dissolved silicic acid and particulate silica. Its concentration often varies spatially and temporally within a lake. Lower concentrations are typically measured in the upper waters (epilimnion) during the winter and early spring period of complete mixing. Spring diatom blooms are common in Cayuga Lake; the concentration of dissolved silica declines as the nutrient is assimilated into phytoplankton cells. An increase in silica concentration above the sediments is typical of many lakes during summer stratification (Wetzel 1983). The LSC field investigations detected consistently low concentrations of silica, with greater variability in the shallow region than in the area of the proposed intake.
Dissolved oxygen (DO) is a water quality characteristic that is closely linked to trophic state. In lakes such as Cayuga that thermally stratify during the summer, the lower waters are isolated from the air above the lake, preventing atmospheric exchange of oxygen. The maximum oxygen content of the lake's lower waters is fixed once stratification occurs, and declines throughout the stratified period due to respiration and microbial decomposition. The rate of the decline and the annual minimum DO concentrations reflect the lake's level of productivity. In Cayuga Lake, hypolimnetic dissolved oxygen concentrations remain high throughout the stratified period, indicating that Cayuga Lake is in the early stages of mesotrophy. A typical August profile of temperature, DO concentration, and percent DO saturation with depth (Figure 2.3.1-6) indicates minimal DO depletion in the lake's lower waters. Water temperature and dissolved oxygen concentrations measured during 1995 in the region of the proposed LSC intake (Station S11) demonstrate the gradual decline in hypolimnetic DO during the stratified period (Figure 2.3.1-7). The amount of DO depletion depends on the balance between supply and demand; in Cayuga Lake the oxygen available in the large volume of the hypolimnion is significantly greater than the demand posed by decomposition and respiration.
Chloride concentrations in surface waters typically reflect the underlying geology of the watershed, but may be altered by human activities such as industrial discharges, road salting, or sewage disposal. Cayuga Lake chloride concentrations have historically been elevated compared to other regional lakes (with the exception of Seneca Lake, which also contains high concentrations of sodium and chlorides), and to the lake tributaries' inflow concentrations. Likens (1974) reported a significant chloride imbalance in Cayuga Lake, with the annual discharge some 95 percent greater than the annual income. These data suggest a significant source, or sources, of chlorides within the basin of Cayuga Lake.
Several hypotheses have been developed to explain the elevated chlorides. Berg (1966) considered that the Cayuga and Seneca lake bottoms might be sufficiently deep to intercept groundwater from salt-bearing strata. However, the chloride concentrations in Cayuga Lake have been declining since 1970 (Figure 2.3.1-8), which corresponds to the virtual elimination of an industrial discharge of chlorides from a salt mining operation at Portland Point. A mass balance analysis of Cayuga Lake chloride concentration concluded that this industrial source contributed to the elevated chloride concentrations reported in the 1960s, and that the chloride concentration in the lake would continue to decline in response to lake flushing (Effler, Auer, and Johnson 1989). The chloride concentration measured in the 1994 LSC field investigation averaged 40 mg/l, which is significantly lower than concentrations measured prior to the mid-1980s.
The amount of suspended solids in the lake water, and the corresponding turbidity (a measurement of light scattering), fluctuate with depth and season in Cayuga Lake. Suspended solids include both organic and inorganic materials. Seasonal variability measured in the region of the proposed LSC outfall is high in response to algal blooms and sediment inputs through the tributaries. There is less variability in suspended solids and turbidity data recorded at the depth of the proposed intake (Figure 2.3.1-9). The amount of particulate material in water is a significant determinant of drinking water quality and the need for treatment.
Total organic carbon (TOC) measurements were collected as part of the LSC field investigations. Similar to suspended solids, the TOC concentration in lake water will vary with depth and time, and in response to both tributary inflows and in-lake processes. Productivity gradients with depth during the stratified period contribute to the vertical distribution of TOC. In Cayuga Lake, the TOC concentration is generally less than 5 mg/l in the surface waters, and less than 3 mg/l at the depth of the proposed intake.
Cayuga Lake waters are moderately hard, with a bicarbonate alkalinity of approximately 100 to 110 mg/l as CaCO3 and hardness of 160 mg/l. Measurements of pH (although variable with depth, season, and time of day) are consistently within the alkaline range.
2.3.1.6 Food Web.
The Cayuga Lake food web can be considered to include two interrelated assemblages of species, one in the shallow (littoral) zone, and the second overlying the deeper water. Cayuga Lake's littoral zone is limited to the northern and southern lake basins and a narrow fringe along the lake margins, where light reaches the lake bottom. Approximately 25 percent of the lake's surface area overlies depths of 6.1 m (20 ft) or less. The shallow areas, found mostly in the lake's northern basin, are considered to represent littoral habitat for warmwater fish (Chiotti 1980).
Phytoplankton (including cyanobacteria or blue-green algae), benthic algae, and rooted aquatic plants and algae (macrophytes) form the base of the autotrophic food web. The species composition of these communities is described in Section 2.3.3, Phosphorus and Productivity. In general, the phytoplankton community includes a diverse assemblage of species representing all major taxa. Godfrey (1977) identified a total of 217 algal species in Cayuga Lake in the early 1970s; of these, 80 species were relatively important components of the flora. Sampling conducted between 1994 and 1996 as part of this investigation indicates that the current phytoplankton species assemblage is generally consistent with the historical record. The 1996 phytoplankton, chlorophyll a, and transparency data indicate that the biovolume of phytoplankton in the southern lake basin is lower than that measured in 1994 and 1995. Zebra and quagga mussels are a possible cause of the reduced phytoplankton, as discussed further in Section 2.3.3.
Zooplankton form the second trophic level in Cayuga Lake, grazing on phytoplankton and providing food to many of the lake's fish, at least during portions of their life cycle. Oglesby (1978) has reviewed the historical zooplankton species composition data and concluded that the Cayuga Lake community is typical of a moderately productive, north temperate lake. Data collected in 1994 as part of the preliminary LSC environmental feasibility analysis generally support this conclusion.
Cayuga Lake has a large population of Mysis relicta, a zooplankton found in the lower waters and, at times, associated with the benthos. M. relicta is an important component of the Cayuga Lake food web, and has been the focus of detailed field investigations of the potential environmental impacts of LSC. The animal is an opportunistic omnivore, feeding on detritus, benthic invertebrates, phytoplankton, and other zooplankton (Lasenby, Northcote, and Fürst 1986). M. relicta are preyed upon by many of the Cayuga Lake fish, including alewives, smelt, sculpin, and juvenile lake trout, and probably compete with the same fish for zooplankton (Rudstam et al. 1989). Chiotti (1980) considers the quantity of M. relicta to be a limiting factor for the growth and survival of stocked juvenile lake trout, Cayuga Lake's most significant sport fishery. The potential for drawing M. relicta into the LSC intake has been closely evaluated, and is discussed in detail in Section 2.3.4.
The benthic invertebrate fauna include crustaceans, insect larvae, oligochaetes, and molluscs. Two exotic molluscs, the zebra mussel (Dreissena polymorpha) and closely related quagga mussel (Dreissena bugensis), are recent and significant additions to the Cayuga Lake benthos. The zebra mussel entered Cayuga Lake through the Seneca River and has spread from north to south in the lake's littoral zone. By the summer of 1996, zebra mussels were well-established in the southern lake basin. Quagga mussels are currently less abundant in the benthic fauna.
Researchers have noted significant alterations to nutrient and energy cycling in other aquatic systems following invasion by these exotic mussels. Benthic invertebrates transform particulate detritus and algal cells into protein that can be used by other animals higher in the food web. In general, the benthic fauna has a greater number of individuals and species in shallower waters, probably reflecting the greater quantities of nutrients and higher microhabitat diversity created by benthic rooted aquatic plants and algae. Proliferation of the exotic mussels (discussed in Section 2.3.6) has the potential to increase the importance of the benthos in nutrient and energy cycling within the lake ecosystem.
The Cayuga Lake fish community can be described in terms of two distinct assemblages, one reflecting the littoral habitats, and the other reflecting the profundal habitats. LSC potentially impacts both assemblages; the intake region includes deepwater habitat, and the outfall region includes littoral habitat. LSC impacts on the Cayuga Lake fish community are discussed in Section 2.3.7.
Most of the littoral habitat is found in the northern lake basin, which is home to a warmwater fishery dominated by smallmouth bass. Other important predator fish in the inshore community include largemouth bass and northern pike. These species prey on yellow perch, pumpkinseeds, bluegills, rock bass, and minnows. The southern lake basin supports a spawning population of white suckers.
The profundal fish community is dominated by lake trout, rainbow trout, brown trout, and landlocked salmon as the top predators. Of these salmonids, only the lake trout is native to Cayuga; other salmonid species were introduced. Populations of the salmonid species are maintained (or, in the case of rainbow trout, supplemented) by stocking. Juvenile salmonids prey on zooplankton, including M. relicta. Older fish feed mainly on other fish, with alewives, rainbow smelt, trout perch, and slimy sculpin important prey. The alewife is the predominant forage species in Cayuga Lake. Youngs and Oglesby (1972) report that the food web supporting the deepwater fishery is rather short, consisting of phytoplankton to zooplankton to alewife to lake trout. The lake trout community is not dependant to a great degree on benthic production. A second energy pathway culminating in smelt begins with organic detritus, which is consumed by M. relicta, which are in turn consumed by smelt. These generalized food webs do not reflect the fact that food preferences change with life stage and size.
The distribution of fish in the water column reflects thermal preference of individuals, and varies with fish size and life stage, season, and time of day. The deep water fish migrate in a predictable manner to spawning areas of tributaries or shallow regions, and may consequently be found in the littoral region during parts of the year.
