The information used to compile the following includes data collected sporadical ly between 1935-87, plus an intensive physical and chemical characterization conducted during 1988 by Iannuzzi (1991a; b), at which time nine sites distributed over the entire surface of the lake were monitored weekly for a full year. There has been a continuing program, initiated in January, 1992, where the deepest and most representative site on the lake (TR4-C) has been monitored at least monthly during ice cover and bi-weekly throughout the remainder of the year. Since that time, laboratory certif ication with the NYSDOH has involved formal quality assurance/quality control protocols.
The alkalinity of the lake water, ascertained by titrating to pH=4.6 with 0.02 N H2SO4, averages around 110-124 mg/l as CaCO3 (range, 1968-94 = 57-173 mg/l as CaCO3, extreme values in eulittoral areas during the winter) with bicarbonate being the predominant alkalinity component. Only during July and August when photosynthetic activity is particularly intense d oes carbonate alkalinity appear temporarily in the trophogenic zone. Changes in the alkalinity fractions are accompanied by pH changes. The highest pH value recorded under these conditions was 8.6. The alkalinity and pH levels of the surface waters preclude a high carbon dioxide concentration; therefore, concentrations range between 0.5 and 2.5 mg/l in those areas. Inversely, the biogenic decomposition of organic matter in the photolytic zone is associated with the liberation of carbon dioxide. Conce ntrations of 6-8 mg/l are normally reached during summer stratification, although measurements in excess of 12 mg/l have been recorded near the bottom. These increased levels of carbon dioxide lead to reduced pH and increased bicarbonate levels in the hypolimnion. This is particularly evident during late summer. Total alkalinity values as high as 138 mg/l and pH values as low as 7.2 have been recorded in the deeper areas of the lake during late summer stagnation (Table 19) (Harman et al., 1980) .
Recorded values for conductivity, pH, calcium, magnesium, sodium, and chloride are comparable, although commonly somewhat greater, than those of the smaller Finger Lakes. Total alkalinity compares with the larger Finger Lakes and smaller bodies of water on the Onondaga limestone belt (Fayetteville Green Lake and Onondaga Lake) (Berg, 1963). This is to be expected because of Otsego Lake's location relative to the local Onondaga limestone formations. One additional interesting feature is tha t the ionic content of the major streams, in practically all cases, exceeds that found in the lake waters (Table 20), giving some indication of the relative impact of stream chemistry as opposed to the quality of precipitation incident on the lake surface. Although excessive chloride levels are not a problem on a lake-wide basis, Peters (1974) tabulated levels measured in the 1920s and from the late 1940s into the late 1970s which illustrate the quadrupling of the chloride content of Otsego Lake durin g that time (Figure 31). No single cultural activity was implicated, but increased road salting and more extensive discharge of septic tank effluent in the watershed parallel the increase in chloride concentrations.
Between 1988 and present, chloride (Cl-) concentrations have been monitored using mercuric nitrate titrations. In 1988, levels throughout the lake ranged from 3.0 mg/l to 39.4 mg/l, with a water column average of 5.8 mg/l (Figures 32,33). However, concentrations throughout the lake demonstrated only slight seasonal and depth variations for all sites with the exception of the Cooperstown waterfront (TR7-C), which exhibited exceedingly high weekly shoreline water column averages on a near regular basis throughout the winter (Figure 32). Excluding the high winter values at TR7-C, weekly and/or monthly Cl- concentrations throughout the lake ranged from 3.0 mg/l to 8.1 mg/l, with a water column average of 5.5 mg/l. Of these sites, water column compa risons in 1988 indicate that Cl- concentrations are spatially and temporally homogeneous (Figures 32,33).
Present (1994) center lake concentrations vary between 6 and 7 mg/l illustrating a reduction in the rate of increase since 1980; this is correlated with a reduction in the use of road salts by the Village of Cooperstown beginning in 1990 (Russell, 1996). However, outflows from Willow Brook, which drain surface waters from the Village, have since been recorded as high as 970 mg/ l (Albright, 1996), indicating that deicing salt use by the private sector and as an anti-caking agent for abrasives by the Cooperstown community may still be substantial.
In 1988 pH values ranged from 7.1 to 8.4, with a water column average of 7.9. The mean epilimnion and shoreline water column average was 8.0, while that of the hypolimnion was 7.7. Conductivity values, which typically increase with depth during periods of stratification, ranged from 178 umho/cm to 313 umho/cm throu ghout the lake with a mean water column average of 282 umho/cm.
In 1988, calcium (Ca2+) concentrations, assessed by atomic absorption spectroscopy, ranged throughout the lake from 20 mg/l to 59 mg/l, with an epilimnion and shoreline water column average of 48 mg/l. Weekly and/or monthly concentrations for the mid-lake sites increased with depth. The exception occurred in April and November samples which were evenly mixed due to spring and fall overturn, respectively. Winter Ca2 + concentrations, particularly for surface samples below the ice, were variable for the shorelines sites, while those of the mid-lake sites were generally consistent (TR4-C, range 38-59 mg/l) from week to week. Epilimnion and shoreline water column averages decreased during the summer months, with the lowest recorded value of 38 mg/l, occurring during the fourth week of August. Fall concentrations consecutively increased from the summer minima during September and October, with mixing occurrin g during the fourth week of November. Yearly epilimnion and shoreline Ca2+ averages indicate spatial homogeneity throughout the lake. Monitoring since 1992, using the titrimetric EDTA method, indicates no significant changes in Ca2+ concentrations.
Magnesium concentrations, measured by atomic absorption sprectroscopy, ranged from 2.1 mg/l to 4.4 mg/l during 1988, with an epilimnion and shoreline water column average of 3.8 mg/l. Spatial and seasonal trends, for the most part, followed those of calcium distributions throughout the year.