Otsego Lake Limnological Monitoring, Willard N. Harman

Transcription

1 11 Otsego Lake Limnological Monitoring, 1994 Willard N. Harman ABSTRACT Limnological analyses of several abiotic factors were performed during the calendar year 1994 at Otsego Lake, Cooperstown, N.Y. The purpose was to monitor the chemical and physical parameters affecting lake water quality for comparison with past findings. This work was part of an ongoing study begun approximately twenty-seven years ago. Measurements using a Hydrolab Surveyor were gathered at the deepest spot in the Lake (TR4-C). Water temperature, dissolved oxygen, ph and conductivity were measured at 2 m intervals from 0 to 20 m and from 40 to SO m, and with 10 m intervals between 20 and 40 m. The data, after comparison with information collected in the past, indicate water quality varies in regard to the volume of cold water fish habitat in late summer. These changes are attributed to fluctuations in nutrient loading and weather conditions. NTRODUCTON Otsego Lake is a glacially formed, dimictic lake supporting a cold water fishery. The Lake is generally classified as being chemically mesotrophic, although flora and fauna characteristically associated with oligotrophic lakes are present (annuzzi, 1991). Since the establishment in 1968 of the field station, limnological investigations have been ongoing (Clikeman, 1979; Godfrey, 1980; Harman, 1974; Harman and Sohacki, 1976; Harman, 1978; Harman, 1979; Harman, 1980; Harman and Sohacki, 1980; Homburger and Buttigieg, 1991; annuzzi, 1988; Monostory, 1972; Sohacki, 1970; Sohacki, 1971; Sohacki, 1972; Sohacki, 1973; Sohacki, 1974; Sohacki, 1975; Starn and Wassmer, 1969). This study is the continuation of year-round work which began in 1991 to monitor lake water quality. The data collected in this report runs for the calendar year and is comparable with contributions by Homburger and Buttigieg (1992), Groff, et. al. (1993), and Harman (1994). MATERALS AND METHODS Data collection for this year's investigation began January 18 and continued until December 27, During winter months (Jan.-Mar.) while the ice covered the surface of the lake, readings were taken monthly. During periods of open water trimonthly or weekly readings were collected. Data was taken near the deepest part of the Lake (TR4-C) (see Figure 1). Past studies have shown the Lake is chemically homogenous (annuzzi, 1988). Through the use of bored holes in the ice or the use of a field station boat, measurements were recorded at 2 m intervals between 0 and 20 m and 40 m to the bottom. Ten (10) meter intervals were used between 20 and 40 m. Measurements of ph, temperature, dissolved oxygen and conductivity were recorded on site with the use of a multiprobe digital microprocessor. Temperature RESULTS Surface temperature reached a high of 23.S o C on July 21 and lows of OOC when under ice. The near bottom temperatures ranged from 2.8 o C on January 18 to S.l o C on September 20 and October 18. The thermocline, a zone where temperatures change rapidly, was usually

2 12 Figure 1. Otsego Lake transects and sample stations. ( G,.90dyeer ~?~O--~North End.:lwamp fim49l'~, 6"1 ) Sanctuarv '-~ '7 ; 648 TR-"r 647 (.55:? ) 78-0 ( (t~'jc!arke Point 645 ~ ~~ \ ~5~.k. 656 \ / ~71 \Hyde Say TR -S \ G~~!, '';J! / 64 t,,,-r--- ;'!! West Shore Rat Cove

3 Figure Otsego Lake dissolved oxygen profiles. sopleths in mg/l. 13 o~~,, :,,----c------:'----~~ ef Depth in Meters January March May July September Figure Otsego Lake dissolved oxygen profiles. sopleths in mg/l ~ 0) Depth in Meters January March May July September November

4 14 found between 8 and 14 m. Temperature stratification was apparent under the ice but was much more prominent during the summer. The first significant summer stratification became apparent on May 2 between 10 and 14 m. The thermocline was completely eliminated by December 13. Dissolved Oxygen Dissolved oxygen concentrations ranged from surface readings of 14.2 mg/l on January 18 to 8.2 mg/l on July 20. Near bottom readings ranged from 10.8 mg/l on May 2 to 0.7 mg/l on October 18 (see Figure 2). Bottom readings were less than 2 mg/l between October 13 and December 13. ph measurements in Otsego Lake ranged from 7.3 at a November 1 to 8.6 at 4 m on June 6. depth of 48 m on Conductivity Conductivity values in Otsego ranged from 277 ohms/em on November 1 and 11 and December 13 at a depth of 48-9 m, to 162 ohms/em on March 21 at the frozen surface. Secchi disk transparency Water transparency ranged from 1.3 m on June 30 and July 7, to a high of 6.3 m on February 21 (through the ice). DSCUSSON Analysis of past and present data collected in this ongoing investigation is important in the monitoring of Otsego Lake. Figure 2 illustrates the distribution of oxygen concentrations throughout the Lake during 1994, Figure 3 during Although similar, the 1993 data illustrate lower November bottom oxygen concentrations. Oxygen concentrations throughout the hypolimion were slightly lower in Hypolimnetic oxygen deficits for 1969,72,88 and (Table 1), as per Hutchinson (1957), indicate increasing eutrophy. Oxygen is closely monitored because of its relationship with nutrient loading and its importance to local cold water fish species. nterval D.O. Deficit (mg/cm A 2/day) 05/16/69-09/27/ /30/72-10/14/ /12/88-10/06/ /18/92-09/29/ /10/93-09/27/ /17/94-09/20/ Table 1. Areal hypolimnetic oxygen deficits, Otsego Lake. Computed over summer stratification in 1969, 1972 (Sohacki, Unpbl.J, 1988 (annuzzi, 1991),

5 15 t should be noted that in October oxygen concentrations were reduced to the point of negatively affecting the cold water fish throughout much of the hypolimnion. This serious threat to the fisheries is a direct result of nutrient introduction into the Lake from a diversity of sources. REFERENCES Clikeman, P preliminary petrography and chemical analysis of Otsego Lake surface sediments. n 11th Annual Report (1978). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Godfrey, P. J Otsego Lake Limnology: phosphorus loading, chemistry, algal standing crop, and historical changes. n 9th Annual Report (1976). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Groff / A., J. Joseph Homburger and W. N. Harman Otsego Lake limnological monitory, n 24th Annual Report (1991) SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Harman, W. N Bathymetric map of Otsego Lake. Otsego County Conservation Association, Cooperstown. Harman, W. N Otsego Lake Water Levels. n 11th Annual Report (1978). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Harman, W. N Otsego Lake limnological monitoring, n 26th Annual Report (1993). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Harman, W. N. and L. P. Sohacki A basic limnology of Otsego Lake (summary of research ) SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta, Occasional Paper 3:1-50. Harman, W. N., L. P. Sohacki, and P. J. Godfrey The limnology of Otsego Lake. n Bloomfield, J. A. (ed.) Lakes of New York State. Vol.. Ecology of East-Central N. Y. Lakes. Academic Press, nc., New York. pp Homburger, J. Joseph and Gavin Buttigieg Otsego Lake limnological monitoring. n 24th Annual Report (1991). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Hutchinson, G. E A treatise on limnology. Vol. 1. Geography, physics and chemistry. Wiley, New York. annuzzi, T. J A model plan for the Otsego Lake watershed. Phase : The chemical limnology and water quality of Otsego Lake, Occasional Paper #23, SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Monostory, L. (Edited L. P. Sohacki, W. N. Harman) Stream-lake productivity relations in the Otsego Lake watershed. n 4th Annual Report (1971). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Sohacki, L. P Limnological research. n 3rd Annual Report ( ). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. p. 44. Sohacki, L. P Limnological aspects of Otsego Lake. n 3rd Annual Report ( ). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. p. 44. Sohacki, L. P Limnological investigations. n 4th Annual Report (1971) SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Sohacki, L. P Limnological studies on Otsego Lake. n 5th Annual

6 16 Report (1972). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Sohacki, L. P Limnological studies. n 6th Annual Report (1974). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Sohacki, L. P Limnological studies on Otsego Lake. n 7th Annual Report (1975). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Starn, J. and D. Wassmer A limnological study of Otsego Lake and Moe Pond. n 1st Annual Report (1969). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp. 12 and 21.