Otsego Lake limnological monitoring, 1998

Transcription

1 11 Otsego Lake limnological monitoring, 1998 Matthew F. Albright l ABSTRACT Limnological analyses of several abiotic factors were performed during 1998 on 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 is part of an ongoing study begun thirty years ago. Throughout the year, profiles of water temperature, dissolved oxygen, ph and conductivity were measured using a Hydrolab Scout 2 at the deepest spot in the Lake (TR4-C). Water samples were collected in profile for the analyses of total phosphorus, nitrite+nitrate, calcium, chloride, and alkalinity. Photic-zone composite samples were collected for chlorophyll (J determinations. Secchi disk transparency was measured. The data, after comparison with earlier information, indicate water quality varies in relation to the volume of cold water fish habitat in late summer. These changes are attributed to fluctuations in nutrient loading, weather conditions, and food web alterations due to the proliferation of the alewife. INTRODUCTION 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 (Iannuzzi, 1991). Since the establishment in 1968 of the Biological 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; Iannuzzi, 1988; Monostory, 1972; Sohacki, 1970; 1971; 1972; 1973; 1974; 1975; Starn and Wassmer, 1969). This study is the continuation of year-round protocol which began in The data collected in this report runs for the calendar year and is comparable with contributions by Homburger and Buttigieg (1992), Groff, et. af. (1993), Harman (1994; 1995) Austin et at. (1996), and Albright (1997; 1998). MATERIALS AND METHODS Data collection began 3 April and continued until 16 December Readings were collected weekly or bi-weekly. Tenuous ice conditions prevented sampling during winter 1Staff assistant, SUNY Oneonta, BFS

2 12 months. Data were collected near the deepest part of the Lake (TR4-C) (Figure I), which is considered representative as past studies have shown the Lake to be spatially homogenous with respect to the factors under study (Iannuzzi, 1988). Physical measurements were recorded at 2 m intervals between 0 and 20 m and 40 m to the bottom; 5 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 Hydrolab Scout 2 multiprobe digital microprocessor which had been calibrated according to manufacturer's instruction immediately prior to use (Hydrolab Corp., 1993). Samples were collected for chemical analyses at 4 m intervals between 0 and 20 m and 40 m and the bottom; 10m intervals were used between 20 and 40 m. A summary of methodologies employed for chemical analyses are given in Table I. Composite samples were collected through the photic zone (surface to the depth at which light equals I% ambient levels, determined with a Protomatic photometer) for chlorophyll (J determinations. When variable light conditions precluded accurate photometric readings, sampling depth was to the Secchi depth times 2.7, which has been used as an estimator of the photic zone (Wetzel and Likens, 1991). Chlorophyll (/ measurements were made using a Turner Designs TD-700 fluorometer following the methods of Welschmeyer (1994). Temperature RESULTS AND DISCUSSION Surface temperature reached a high of C on 23 July and lows ofooc when under ice. The near-bottom temperatures reached 4.91 on 4 December. Winter profiles were not recorded due to thin ice. According to the US Weather Service, the lake froze IS February, though some reported several acres of open water throughout the winter. Summer stratification was apparent by mid May. The thermocline was completely eliminated by December 16. Dissolved Oxygen Dissolved oxygen concentrations ranged from surface readings of mg/l on 17 April to 8.36 mg/l on 8 October. Near-bottom readings ranged from mg/l on 3 April to 0.81 mg/l on 19 November (Figure 2). Areal hypolimnetic oxygen depletion rates were similar to those of the 1990's, which are significantly higher than were measured historically (Table 2). Current values greatly exceed the lower limit of eutrophy (0.05 mg/cm 2 /day) suggested by Hutchinson (1957).

3 13 CRIPPLE CREEK CLARKE POND BLACKBIRD BAY WILLOW BROOK SUSQUEHANNA RIVER Figure 1. Bathymetric map of Otsego Lake showing sampling site (TR4-C).

4 Parameter Sample Vol. Preservation Method Reference Total Phosphorus-P 40 ml H 2 S0 4 to ph<2 Persulfate digestion followed By single reagent ascorbic acid EPA,1983 Nitrite+Nitrate 25 ml Filter and cool To <4 C Cadmium reduction APHA,1989 Calcium 50 ml None EDTA titrimetric method EPA Chloride 100 ml None Mercuric nitrate APHA,1989 Alkalinity 100 ml Cool to <4 C, Measure ASAP Titration to ph=4.6 APHA.1989 Table 1. Summary oflaboratory methodologies,

5 Depth in Meters I I January March I I I I May JUly September November Figure Otsego Lake dissolved oxygen profiles. Isopleths in mg/l.

6 16 Interval 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/ /19/95-10/10/ /14/96-09/17/ /08/97-09/25/ /15/98-09/17/ Table 2. Areal hypo1imnetic oxygen deficits, Otsego Lake. Comuted over summer stratification in 1969, 1972 (Sohacki, Unpubl.), 1988 (Iannuzzi, 1991) and * *' *' 7 ' OJ 6 5 OJ u 5. E 0 *' 4 '* *"" '* *' 3 '* '* '* *' *' 2 1 *' *'*'*' *' **'" '* *"'* '* Figure 3. Mean chloride concentrations at TR4-C, Points later thatn 1990 represent yearly averages (modified from Peters, 1974).

7 17 ph measurements in Otsego Lake ranged from 7.08 near the bottom on 6 August to 8.43 at the surface on 11 June. Alkalinity Alkalinity averaged 109 mg/i (as CaC0 3 ) throughout the year. The minimum value of 90 mg/l was observed at the surface on 31 August and 17 September; the maximum value (123 mg/i) occurred at 48 m on 19 November. These data are consistent with earlier findings (Harman et ai., 1997). Calcium Calcium dynamics paralleled those of alkalinity. The year-long average was 45.3 mg/1. A low of 37.7 mg/l was encountered at 4 m on 17 September; a high of 50.5 was observed at 44 and 48 m on 19 November. Conductivity Conductivity (an indirect measure of ions in solution) values in Otsego ranged from 233 mmhos/cm at the surface on 17 September to 285 mmhos/cm at 48 m on 8 October. Chlorides Chloride concentrations averaged 9.7 mg/i, exhibiting very little variation either temporally or spatially. The trend of increasing chloride levels, first recognized in the 1950s (Peters, 1987), presumably attributable to road salting, continues (Figure 3). Concentrations are approximately 0.7 mg/l higher than in Assuming sodium chloride is the source, this represents an addition of about 400,000 kg (440 tons) of salt to the lake in the past year. These increases are despite the Village of Cooperstown's continuing efforts to limit salt as an anti-icing compound. In the future it cannot be assumed that NaCI is the sole source of chlorides, as local municipalities have begun to use a deicer that contains significant levels of MgCl. Nutrients Total phosphorus-p ranged from 5.3 ug/l at 40 man 20 August to 23.9 ug/l at 8 m on 6 August and averaged 9.9 ug/1. Nitrite+nitrate-N ranged from 0.28 mg/l at the surface on 5 November to 0.92 mg/l at 30 m on 20 August and averaged 0.65 mg/l. There was no evidence of phosphorus release from the sediments prior to fall turnover, as had been suggested following 1995 monitoring (Harman et ai., 1997).

8 18 Chlorophyll a Photic-zone mean chlorophyll a concentrations ranged from 3.3 ug/l(3 April) to 9.8 ug/i (4 December). The mean value over the collection period (3 April to 4 December) was 5.6 ug/l. While seasonal trends were quite different than in 1997, the range and mean was similar data, as well as those concerning Secchi transparency, are presented in full in Figure 4. Secchi disk transparency Water transparency averaged 2.8 m (the lowest mean transparency on record) and ranged from 0.9 m on 2 July to a high of 4.2 m on 5 November. Secchi transparencies, coupled with chlorophyll (J photic zone means, are shown in Figure 4. Figure 5 summarizes annual mean Secchi transparencies at TR4-C in 1935, , , , 1988, and (Harman et al., 1997). REFERENCES Albright, M.F Otsego Lake lim no logical monitoring, In 29 th Annual Report (1996). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Pp Albright, M.F Otsego Lake lim no logical monitoring, ill 30 th Annual Report (1997). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Pp APHA, AWWA, WPCF Standard methods for the examination of water and wastewater, 17 th ed. American Public Health Association. Washington, DC. CI ikeman, P Prel il11 inary petrography and chemical analysis of Otsego Lake surface sediments. ill 11th Annual Report (1978). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp EPA Methods for the analysis of water and wastes. Environmental Monitoring and Support Lab. Office of Research and development. Cincinnati, OH. Godfrey, P Otsego Lake Limnology: phosphorus loading, chemistry, algal standing crop, and historical changes. ill 9th Annual Report (] 976). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Groff, A., 1. Joseph Homburger and W. N. Harman Otsego Lake limnologicaj monitory, In 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. ill 11th Annual Report (1978). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp. 3-5.

9 19 10, Chlorophyll a )K Secchi Depth nj >..c 0.. o I. o..c o 3 : : ,------, /24 04/15 06/04 07/24 09/12 11/01 12/ Figure 4. Mean photic zone chlorophyll a concentrations (parts per billion) and Secchi depth transparency (meters), 1998.

10 -- u- - r- r f E r >. () C Q.) -3 f - r- " CO Q.. (f) C CO -4 f-- I-.::s::. (f) is r r- -- I ---- ;-..c () () Q.) (f) -,.. '-- c '69 '70 '71 '72 '73 75 '76 '77 '78 '79 '80 '81 '82 84 '85 '86 '87 '88 92 '93 '94 '95 '96 '97 '98 Year Figure 5.Annual means of Secchi depth transparency, collected at TR4-C, (modified from Harman et ai., 1997). I\) o

11 21 Harman, W. N Otsego Lake limnological monitoring, 1994.ln 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: Harman, W. N., L. P. Sohacki, and P. J. Godfrey The limnology of Otsego Lake. In Bloomfield, J. A. (ed.) Lakes of New York State. Vol. III. Ecology of East-Central N.Y. Lakes. Academic Press, Inc., New York. pp.l-128. Harman, W.N., L.P. Sohacki, M.F. Albright, and D.L. Rosen The state of Otsego Lake, Occasional Paper #30, SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. Homburger, 1. Joseph and Gavin Buttigieg Otsego Lake limnological monitoring. In 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. Hydrolab Corporation, Scout 2 operating manual. Hydrolab Corp. Austin, TX. Iannuzzi, T A model plan for the Otsego Lake watershed. Phase II: 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. In 4th Annual Report (1971). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Peters, T Update on chemical characteristics of Otsego Lake water. In 19th Annual Report (1986). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Sohacki, L. P Limnological research. In 3rd Annual Report ( ). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. p. 44. Sohacki, L. P Limnological aspects of Otsego Lake. In 3rd Annual Report ( ). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. p. 44. Sohacki, L. P Limnological investigations. In 4th Annual Report (1971). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Sohacki, L. P Limnological studies on Otsego Lake. In 5th Annual Report (1972). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp Sohacki, L. P Limnological studies. In 6th Annual Report (1974). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp

12 22 Sohacki, L. P Limnological studies on Otsego Lake. In 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. In 1st Annual Report (1969). SUNY Oneonta Bio. Fld. Sta., SUNY Oneonta. pp. 12 and 21. Welschmeyer, N.A Fluorometric analysis of chlorophyll a in the presence of chlorophyll b and pheopigments. Limnol. Oceanogr. 39: