Otsego Lake limnological monitoring, 2010

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1 Otsego Lake limnological monitoring, 2010 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, 1992). This study is the continuation of 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; 2000; 2001; 2002; 2003; 2004; 2005; 2006; 2007; 2008), Albright and Waterfield (2009), and Waterfield and Albright (2010). Concurrent additional work related to Otsego Lake included estimates of fluvial nutrient inputs (Putnam 2011), and descriptions of the zooplankton community (Albright and Leonardo 2011), chlorophyll a (Bauer 2011), and nekton communities (Bowers 2011; Waterfield et al. 2011). 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 monthly though the ice in February and March, approximately bi-weekly during open water conditions April through October, and monthly in November and December; samples were not collected in January 2010 due to marginal ice conditions. 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 with the use of a Hydrolab Scout 2 or a Eureka Manta multiprobe digital microprocessor which had been calibrated according to the manufacturer s instructions prior to use (Hydrolab Corp. 1993; Eureka Environmental Engineering 2005). Samples were collected for chemical analyses at 4-m intervals between 0 and 20 m and 40m and 48m; 10-m intervals were used between 20 and 40 m. A summary of methodologies employed for sample preservation and chemical analyses is given in Table 1. Data for a particular parameter were omitted from analysis in a few cases where equipment malfunction or miscalibration was suspected following further scrutiny. 1 Research Support Specialist, SUNY Oneonta Biological Field Station. 2 Assistant to the Director, SUNY Oneonta Biological Field Station.

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 Reference Total Phosphorus H 2 SO 4 to ph < 2 Persulfate digestion followed by single reagent ascorbic acid Liao and Marten 2001 Total Nitrogen H 2 SO 4 to ph < 2 Cadmium reduction method following peroxodisulfate digestion Pritzlaff 2003; Ebina et al Nitrate+nitrite-N H 2 SO 4 to ph < 2 Cadmium reduction method Pritzlaff 2003 Ammonia-N H 2 SO 4 to ph < 2 Phenolate method Liao 2001 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 RESULTS AND DISCUSSION Temperature Figures 2a and 2b depict temperatures measured in profile (0 to 48m) at site TR4-C from 23 February through 2 December Surface temperature ranged from 0.61 o C below the ice on 23 February to 25.5 o C on 15 July. Temperatures at 48m reached the annual minimum of 2.7 o C on 18 March. Spring turnover occurred between 5 April and 18 May, with thermal stratification established by 26 May. Surface temperatures began to decrease after the profile collected 12 August and the thermocline occurred at greater depth until fall turnover, which occurred sometime between 2 December (Figure 2b) and 6 January Dissolved Oxygen Isopleths of oxygen concentration based on the profiles for the calendar year are presented in Figure 3. On 5 April, Prior to the onset of thermal stratification (May), dissolved oxygen below 40m averaged 11.3 mg/l. Dissolved oxygen concentrations in the hypolimnion remained above 6 mg/l through part of August, falling below this level with a concentration of 5.45 mg/l observed at 48m on 12 August. Minimum observed mean DO concentration below 40m was 3.5 mg/l, recorded on 26 October. This minimum is greater than that observed in 2009, when concentrations below 40m had decreased to an average of 1.2 mg/l, and DO was essentially depleted below 44m (Waterfield and Albright 2010). No anoxic conditions were observed in The areal hypolimnetic oxygen depletion rate (AHOD), calculated at mg/cm 2 /day, was lower than that observed since 1988 (Table 2).

4 Depth (meters) Temperature ( o C) /23/2010 3/18/2010 4/5/2010 5/18/2010 5/26/2010 6/4/2010 6/15/ /1/2010 2a /15/2010 Depth (meters) Temperature ( o C) /15/2010 8/3/2010 8/12/2010 8/26/2010 9/9/ /7/ /26/ /10/ /2/2010 2b. 50 Figure 2. Otsego Lake temperature profiles ( o C), as observed at site TR4-C between 23 February and 15 July (2a) and 15 July and 2 December 2010 (2b).

5 Table 2. Areal hypolimnetic oxygen deficits (AHOD) for Otsego Lake, computed over summer stratification in 1969, 1972 (Sohacki, unpubl.), 1988 (Iannuzzi, 1991), and AHOD Time Interval (mg/cm^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/ /20/99-09/27/ /11/00-09/14/ /17/01-09/13/ /15/02-09/26/ /16/03-09/18/ /20/04-09/24/ /27/05-10/05/ /4/06-09/26/ /18/07-9/27/ /8/08-10/7/ /27/09-10/19/ /26/10-10/7/ Conductivity (indirect measure of ions in solution) Mean conductivity in 2010 was 290 µmho/cm, ranging from a minimum of 162 µmho/cm at the surface to a maximum of 330 µmho/cm at 44m; both extremes were observed under the ice on 18 March. Conductivity distribution within the water column followed patterns associated with thermal stratification, with conductivity generally increasing the hypolimnion until fall turnover. ph Mean 2010 ph value at TR4-C was 8.11; ph was highest in the upper 10m on 26 May, with an average value of The lowest mean ph in the upper 10m was observed 18 March, at This range is larger than seen in 2009 (7.94 to 8.61) (Waterfield and Albright 2010).

6 Alkalinity Figure 3. Distribution of dissolved oxygen (isopleths in mg/l) as recorded in 2010 at TR4-C on Otsego Lake. Points along the x-axis indicate profile observation dates. Alkalinity (mg/l as CaCO 3 ) demonstrated seasonal distribution throughout the water column, as inorganic carbon cycling (tied mainly to photosynthesis) greatly influences alkalinity. The maximum gradient was observed on 12 August; illustrates this gradient (low alkalinity in the epilimnion) and provides a comparison to samples collected on 5 March, prior to high rates of photosynthetic activity. Depth (meters) Alkalinity (mg/l as CaCO 3 ) /5/2010 8/12/ /2/2010 Figure 4. Alkalinity (mg/l as CaCO 3 ) determined for Otsego Lake samples collected in profile at TR4- C on 4 April, 12 August, and 2 December 2010.

7 Calcium Calcium concentrations followed a typical seasonal pattern of fluctuation, though minimal stratification was observed during the growing season. Mean annual concentration at TR4-C was 48.3 mg/l, ranging from 23.2 mg/l at the surface to 53.7 mg/l at 44m, both determined for samples collected 18 March. Chlorides Mean chloride concentrations in Otsego Lake from 1925 to 2010 are shown in Figure 5. Between 1994 and 2005 mean concentration increased at of rate of 0.5 to 1.0 mg/l per year (Figure 5). An abrupt decline in concentration was observed following a major flooding event in late June Since then, mean annual concentrations have increased steadily from 14.2 (2007) to 15.5 (2010). Annual mean concentration in 2010 was 15.5 mg/l. Chlorides in Otsego Lake are generally attributed to road salting practices, with the greatest influx of the ion during spring snowmelt events or early-winter snow storms. Chloride (mg/l) Year Figure 5. Mean chloride concentrations at TR4-C, Points later than 1990 represent yearly averages (modified from Peters 1987). Nutrients Total phosphorus-p averaged 7 µg/l in 2010, ranging from below detectable levels (< 4 µg/l) on multiple dates to 31 µg/l just beneath the ice on 23 February. The most variation from surface to bottom was seen in the 23 February profile. Concentrations in July and August were below detectable levels (<4 µg/l) during the height of algal production; this corresponds with the lowest Secchi disk transparencies observed during the growing season (Figure 7). 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. Nitrite+nitrate-N averaged 0.43 mg/l; ammonia-n was not measured, as it is generally

8 below detectable levels (<0.02 mg/l) unless dissolved oxygen is completely depleted in the bottom of the hypolimnion. Total nitrogen analyses indicate an average organic nitrogen concentration of about 0.15 mg/l over the year. Secchi disk transparency and chlorophyll a Chlorophyll a concentration was determined for samples collected on 9 dates in Average 0-20m composite chlorophyll a concentration from May through September 2010 was 1.9 µg/l (range 0.6 to 1.7 µg/l), drastically reduced from previous years in terms of range and temporal variability (Waterfield and Albright 2010, Albright and Waterfield 2009). Secchi disk transparencies ranged from 3.5m on 1 July to a season-maximum of 14.3m on 4 June (Figure 7). Mean transparency (May through October) increased in 2010 (Figure 8), up to 7.2m from 3.1m and 5.1m in 2008 and 2009, respectively. Changes are possibly related to the filtration capacity of the growing zebra mussel population, as similar changes in water clarity and chlorophyll a have been documented concurrent with the establishment and growth of zebra mussel populations elsewhere (e.g. Leach 1993, Waterfield, et al. 2011). Also, over summer 2010, Otsego Lake s zooplankton community comprised a higher abundance of Daphnia spp., which had a mean length substantially greater than any year since 1990 (Albright and Leonardo 2011) Otsego Lake Secchi Transparency 18-May26-May 4-Jun 15-Jun 1-Jul 15-Jul 3-Aug 12-Aug 26-Aug 9-Sep 24-Sep 2 Depth (meters) Figure 6. Secchi disk transparency (m) as measured at site TR4-C on Otsego Lake from 18 May 2010 to 24 September 2010.

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