Otsego Lake limnological monitoring, 2014

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1 Otsego Lake limnological monitoring, 214 Holly A. Waterfield 1 and Matthew F. Albright 2 INTRODUCTION Otsego Lake is a glacially formed, dimictic lake (max depth 51m) 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). This study is the continuation of a year-round monitoring protocol that began in The data collected in this report run for the calendar year and are comparable with contributions by Homburger and Buttigieg (1992), Groff et al. (1993), Harman (1994; 1995), Austin et al. (1996), Albright (1997; 1998; 1999; 2; 21; 22; 23; 24; 25; 26; 27; 28), Albright and Waterfield (29), and Waterfield and Albright (2; 211; 212; 213; 214). Concurrent additional work related to Otsego Lake included estimates of fluvial nutrient inputs (Hastings 215), and descriptions of the zooplankton community (Best and Albright 215), chlorophyll a (Freehafer 215), and nekton communities (Best 214, Waterfield and Wells 215). MATERIALS AND METHODS Physiochemical data and water samples were collected near the deepest part of the lake (TR4-C) (Figure 1), which is considered representative of whole-lake conditions, as past studies have shown the Lake to be spatially homogenous with respect to the factors under study (Iannuzzi 1991). Data and sample collection occurred approximately bi-weekly during open water conditions, 3 February through 3 December 214. Physical measurements were recorded at 2-m intervals between and 2 m and 4 m to the bottom; 5-meter intervals were used between 2 and 4 m. Measurements of ph, temperature, dissolved oxygen (mg/l and % saturation), specific conductance, Oxidation-Reduction Potential (ORP), and Chlorophyll a concentration were recorded with the use of a YSI 65 MDS with a 6-Series multiparameter sonde which had been calibrated according to the manufacturer s instructions prior to use (YSI Inc. 29). Samples were collected for chemical analyses at 4-m intervals between and 2 m and 4m and 48m; -m intervals were used between 2 and 4 m. Methodologies employed for sample preservation and chemical analyses are summarized in Table 1. Nutrient and chlorophyll a concentrations were determined for all sampling dates; alkalinity, calcium, and chloride concentrations were determined for one profile date per month. 1 CLM. Research Support Specialist: SUNY College at Oneonta Biological Field Station, Cooperstown, NY. 2 CLM. Assistant to the Director: SUNY College at Oneonta Biological Field Station, Cooperstown, NY.

2 TR4-C Figure 1. Bathymetric map of Otsego Lake showing sampling site (TR4-C).

3 Table 1. Summary of laboratory methodologies. Parameter Preservation Method of Analysis Reference Total Phosphorus H 2 SO 4 to ph < 2 Persulfate digestion followed by single reagent ascorbic acid Liao and Marten 21 Total Nitrogen H 2 SO 4 to ph < 2 Cadmium reduction method following peroxodisulfate digestion Pritzlaff 23; Ebina et al Nitrate+nitrite-N H 2 SO 4 to ph < 2 Cadmium reduction method Pritzlaff 23 Ammonia-N H 2 SO 4 to ph < 2 Phenolate method Liao 21 Calcium Store at 4 o C EDTA trimetric method EPA 1983 Chloride Store at 4 o C Mercuric nitrate titration APHA 1989 Alkalinity Store at 4 o C Titration to ph= 4.6 APHA 1989 Chlorophyll a Filter immediately; store at o C Buffered acetone extraction followed by flourometric detection Welschmyer, 1994 RESULTS AND DISCUSSION Temperature Figures 2a and 2b depict temperatures measured in profile ( to 48m) at site TR4-C from 3 February through 2 July and 14 July through 3 December 214, respectively. Observed surface temperature ranged from a low of.68 o C on 3 February to 22.6 o C on 2 July, at which point the epilimnion extended through 6m depth (Figure 2a). Temperatures just off-bottom (46-48m) reached the annual minimum of 1.95 o C on 3 February, and maximum of 4.56 o C on 3 December. Complete ice-cover formed on 24 January; the lake was completely ice-free on 13 April. Spring mixing was underway during the 21 April sampling event and thermal stratification was evident by 21 May. Maximum surface temperature was recorded on 2 July, after which surface temperatures began to decrease and the thermocline occurred at greater depth until fall turnover, which was ongoing as of the 3 December sampling event (Figure 2b). Dissolved Oxygen Isopleths of dissolved oxygen concentration based on the profiles for the calendar year are presented in Figure 3. On 21 April, prior to the onset of thermal stratification (in May), dissolved oxygen ranged from mg/l at bottom to mg/l at the surface. The minimum observed DO concentration in 214 was 4.39 mg/l recorded on 15 October at 46m. In most years between 1995 and 29, the bottom minimum concentration was near or below 1. mg/l. The areal hypolimnetic oxygen depletion rate (AHOD), calculated at.5 mg/cm 2 /day (between 21 May and 15 October), remains well below the historical average for the fifth consecutive year (Table 2). Alkalinity Alkalinity concentrations followed a typical pattern of seasonal variation, with concentrations decreasing in the epilimnion during the growing season. Mean annual

4 concentration at TR4-C was 123 mg/l, ranging from 71 mg/l at 2m on 21 April to 136 mg/l at 48m on 11 March. 2a. Temperature ( o C) /3/ /11/214 4/21/ /7/ /21/214 6/3/214 6/18/ /2/ b. Temperature ( o C) /14/214 7/29/214 8/14/214 9/3/ /17/214 /2/214 /15/214 /27/214 11//214 12/3/214 Figure 2. Otsego Lake temperature profiles ( o C) observed at TR4-C 3 February through 2 July (2a) and 14 July through 3 December (2b) 214.

5 Figure 3. Distribution of dissolved oxygen (isopleths in mg/l) as recorded in 214 at site TR4-C on Otsego Lake. Points along the x-axis indicate profile observation dates. Calcium Calcium concentrations followed a typical pattern of seasonal fluctuation similar to that of alkalinity. Mean annual concentration at TR4-C was 49.9 mg/l, ranging from 42.1 mg/l at the surface on 2 October to 54.5 mg/l at 48m on 3 February and 14 July. Chlorides Mean chloride concentrations in Otsego Lake from 1925 to 214 are shown in Figure 4. Between 1994 and 25 mean concentration increased steadily at of rate of.5 to 1. mg/l per year (Figure 4). Since then, mean annual concentrations have been variable and have actually trended slightly downwards, likely reflecting flushing of the system that has occurred during major flooding events (26, 211, 213). The mean lake-wide concentration in 214 was 15. mg/l. Chlorides in Otsego Lake have generally been attributed to road salting practices, with the greatest influx of the ion during spring snowmelt events or early-winter snow storms. Nutrients Total phosphorus averaged 6 µg/l in 214, ranging from below detection (< 4 µg/l) on multiple dates to 39 µg/l at 2m on 27 October. Concentrations were nearly homogeneous from surface to bottom on many dates during the growing season while higher, more variable, concentrations were observed occasionally ( 21 May, 18 June, 29 July, and 14 August). No phosphorus release from the sediments was observed prior to fall turnover, as dissolved oxygen was present at concentrations sufficient to maintain iron-phosphorus bonds in sediment materials.

6 Nitrite+nitrate-N averaged.59 mg/l; ammonia-n was not measured, as it is generally below detectable levels (<.2 mg/l) when dissolved oxygen exists in the bottom of the hypolimnion. Total nitrogen analyses, yielding a mean of.72 mg/l, indicate an average organic nitrogen concentration of about.13 mg/l over the year. The concentration of nitrate-n was higher than in recent years, while Total Nitrogen was nearly identical and the organic fraction was slightly lower (Waterfield and Albright 211, 212, 213, and 214). Table 2. Areal hypolimnetic oxygen deficits (AHOD) for Otsego Lake, computed over summer stratification in 1969, 1972 (Sohacki, unpubl.), 1988 (Iannuzzi, 1991), and Time Interval AHOD (mg/cm 2 /day) 5/16/69-9/27/69.8 5/3/72 - /14/ /12/88 - /6/ /18/92-9/29/ //93-9/27/ /17/94-9/2/ /19/95 - //95.2 5/14/96-9/17/96.9 5/8/97-9/25/97.1 5/15/98-9/17/ /2/99-9/27/ /11/ - 9/14/.9 5/17/1-9/13/1.92 5/15/2-9/26/2.87 5/16/3-9/18/3.87 5/2/4-9/24/4.2 5/27/5 - /5/5.85 5/4/6-9/26/6.84 5/18/7-9/27/7.83 5/8/8 - /7/8.88 5/27/9 - /19/9.82 5/26/ - /7/.53 5/19/11 /12/11.6 5/24/12 /5/ /21/13 /15/ /21/14 /15/14.5

7 Chloride (mg/l) Year Figure 4. Mean chloride concentrations at TR4-C, Points later than 199 represent yearly averages (figure modified from Peters 1987). Chlorophyll a and Secchi Disk Transparency Chlorophyll a concentrations were determined for samples collected on seven dates from June through September 214. Average -2m composite chlorophyll a concentration was 1.7µg/l (range = 1.1 to 2.4 µg/l). Temporal and spatial distribution of chlorophyll a was studied in June and July is discussed by Freehafer (215). Secchi disk transparency measurements, presented in Figure 5, began the growing season at a season-maximum of 7.3m, reaching the lowest observation of 5.m on 18 June. The temporal variation of transparency differed from that observed since 2; May-September transparency measurements for 2 through 214 are presented in Figure 5. Mean summer Secchi transparencies for all years available ( ) are given in Figure 6. Mean transparency was on par with previous years, though individual observations were less variable (range: 5. to 7.3), encompassing a smaller range, with a growing season mean of 6.28m. CONCLUSIONS As was described in Waterfield and Albright (214), lake conditions have been variable from year to year as interactions between management efforts and invasive species continue to develop. Trophic cascade has been described, linking recent changes in water quality to the combined effects of zebra mussel (Dreissena polymorpha) establishment (around 27) and the walleye (Sander vitreus) stocking program that was intended to control the population of alewife (Alosa pseudoharengus) (an invasive forage fish). Region 4 Fisheries Biologists are currently evaluating the lake trout, walleye, and whitefish populations and have adjusted stocking programs accordingly. The sudden decrease in alewife abundance, while a management success, was unexpected and has left the lake trout without an important component of its winter diet.

8 214 NYS DEC gill net catch indicates decreased fitness of adult lake trout and an absence of juveniles, both of which are impacts of decreased forage fish abundance. Gill net catch also included lake whitefish, a native cold-water species, representing multiple age classes; this catch, together with the presence of many lake whitefish fry in larval fish samples, indicates ongoing recruitment by this once-prominent planktivore Figure 5. May through September Secchi transparencies at TR4C, Otsego Lake, 2 through 214.

9 Year Secchi Transparency (m) Figure 6. Mean summer (May through September) Secchi disk transparency collected at TR4-C, REFERENCES Albright, M.F Otsego Lake limnological monitoring, In 29 th Ann. Rept. (1996). Albright, M.F Otsego Lake limnological monitoring, In 3 th Ann. Rept. (1997). Albright, M.F Otsego Lake limnological monitoring, In 31 st Ann. Rept. (1998). Albright, M.F. 2. Otsego Lake limnological monitoring, In 32 nd Ann. Rept. (1999). Albright, M.F. 21. Otsego Lake limnological monitoring, 2. In 33 rd Ann. Rept. (2). Albright, M.F. 22. Otsego Lake limnological monitoring, 21. In 34 th Ann. Rept. (21).

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