Chlorophyll a and phytoplankton survey, Otsego Lake, 2009 1
Irene Primmer 2
INTRODUCTION
In the summer of 2009 Otsego Lake was surveyed for both algal composition and
chlorophyll a concentration. The purpose of the research was to assess the temporal and spatial
variability of algal abundance and community composition in Otsego Lake. Chlorophyll a
concentration was also analyzed to assess the relationship between the amount of Chlorophyll a
present, algal abundance, and the taxonomic composition of the community.
Algae are non-embryonic, non-vascular, oxygenic photoautotrophs whose primary
photoreceptive pigment is chlorophyll a (Dillard 1999). Aquatic algae inhabit a variety of
environments, occupying various niches in a body of water. Phytoplanktonic algae, which are
suspended or swim freely in open water, are the focus of this study. The type of algae present
and their abundance in an aquatic system can reflect a lake’s trophic status and may be indicative
of contamination from the addition of nutrients from agriculture run-off or sewage (Prescott
1964). Conditions of salinity, size, depth, transparency, nutrient conditions, pH, and pollution
effect the composition and abundance of algae present in a body of water (Sheath and Wehr
2003), thus the algal composition is, to some degree, a reflection of the condition of a body of
water.
Most phytoplankton are microscopic, making it difficult to quantify the population in
terms of absolute numbers of individual algal cells. To get around this, photosynthetic pigments
present in such organisms can be quantified in order to estimate the abundance of organisms
present within a body of water. All photosynthetic organisms contain pigments that are employed
to help absorb specific wavelengths of light from the sun’s color spectrum. These wavelengths
provide energy to assist in the electron transport aspect of photosynthesis. This aids in the
production of energy for the specific organisms. Chlorophyll a is a pigment that is found in most
photosynthetic organisms, so its quantification is used as an indicator of the amount of
photosynthetic material in water bodies.
As described by Stevenson and Smol (2003), surveys to determine the taxonomic
composition of algae in the phytoplankton community are a useful means by which to assess
biotic integrity and begin to diagnose causes of environmental problems. Changes in assemblage
should reflect physical and chemical changes caused by perturbations of the system, whether
caused by human actions or changes in the trophic composition. Species presence and success in
community assemblages are ultimately constrained by environmental conditions and interactions
with other species in the habitat (i.e. grazing by zooplankton and zebra mussels, trophic cascades
that impact grazing populations, etc.).
1
2
Support provided by the Otsego County Conservation Association. Peterson Family Conservation Trust Fellow 2009. Current Affiliation: Mansfield University, Mansfield, PA.
Phytoplankton studies were first conducted on Otsego Lake during a biological survey of
the Delaware and Susquehanna watersheds in the summer of 1935 (Tressler and Bere 1936).
During this study total cell counts were performed within selected taxonomic groups of algae and
measures of total suspended solids were also performed. In 1968 the field station performed
surveys of Otsego Lake where there were intense blooms of blue-green algae dominated by
Anabaena (Harman et al. 1996). Such blooms affected Secchi transparencies throughout the lake
were reduced to 2 meters or less because of the increase of particles of phytoplankton within the
water. These blooms indicated nutrient enrichment (Harman et al. 1996). Since then,
phytoplankton research has continued in the fashion of chlorophyll a testing as well as nonregular surveys to study the algal composition of the water in relation to its health.
MATERIALS AND METHODS
Samples were collected at 3 sites on Otsego Lake on 24 June, 10 and 23 July 2009
(Figure 1 and Table 1). A Van Dorn sampler was used to collect about 250 mL of water from 1
meter, 2 meter, and 3 meter depths. Samples were immediately split into subsamples for
chlorophyll a and phytoplankton analyses; equal volumes of each discrete depth sample were
combined into a single 0-3m composite sample. The methods of sample preservation, storage,
and analysis are given in the following sections.
Chlorophyll a
Samples were kept on ice immediately following collection and during transport. In the
lab, two 100mL portions of each sample were run through Whatman GF-A filters in a vacuum
assembly. The filters were frozen until further processing. On the day of analysis, the filters were
cut into small pieces and placed in a glass tube to which 10 mL of a buffered acetone solution
were added. This mixture was ground to a homogeneous slurry using a power drill with a teflon
bit. The slurry was centrifuged at 2,100 rpm for 10 minutes to separate the solution from the
filter paper. A fluorometer was used to determine the fluorescence of the supernatant according
to the methods of Welschmyer (1994). Reported concentrations for samples run in duplicate
represent the average of the concentrations determined for each replicate.
Phytoplankton
100 mL were poured into a separate container and preserved with Lugol’s solution. In
the lab, the samples were set aside to settle for at least 24 hours. A total of 5 mL from the settled
portion of each sample were surveyed for the following phytoplankton taxa according to Prescott
(1954): Chlorophyta, Cyanophyta, Chrysophyta, and Pyrrophyta. For each sample, 1 mL of the
settled portion of sample was added to a Palmer-Maloney slide and examined in entirety using a
digital compound microscope. This was repeated 5 times so that a total of 5 mL was examined.
Prescott (1954) was used as a reference for grouping the algae.
OL 1
OL 2/Tr4-c
OL 3
Figure 1. Otsego Lake, Otsego County, New York showing locations of summer 2009 sample
sites.
Table 1. The site names and corresponding GPS Coordinates for Otsego Lake samples (WGS 84
Degrees Decimal Minutes).
Site Name
OL-1
OL-2 (TR4-C)
OL-3
GPS Coordinates (D mm.mmm)
N 42 48.212’, W 74 53.557’
N 42 45.436’, W 74 53.757
N 42 42.759’, W 74 55.137’
RESULTS AND DISCUSSION
Chlorophyll a concentrations
Chlorophyll a concentrations for 0-3m composite samples are presented in Figure 2 and
Table 2. Across all three sites, concentrations were highest on 24 June (average of 5.6 ppb); the
greatest concentration of the sampling period, 6.0 ppb, was observed on this date at OL-1.
Samples collected on 10 and 23 July had much lower average concentrations (0.7 and 0.6 ppb,
respectively). OL-3 yielded the lowest concentration of the sampling period, 0.3 ppb, on 23 July
(Figure 2, Table 2). Temporal variation was evident, though spatial variation was not apparent.
More robust sampling efforts would more decisively and accurately determine variation on such
gradients; ideally, a greater number of sampling dates and additional analyses for nutrients,
major ions, and environmental factors should also be conducted to assess the spatial distribution
of the community. Interestingly, samples with high chlorophyll a concentrations did not
correspond to those having high individual cell counts (Table 3). This highlights the complexity
of estimating communities with a single metric, such as chlorophyll a, as the amount of
chlorophyll a within a single cell varies among taxonomic groups (Sheath and Wehr 2003).
2009 Chlorophyll a Concentrations 0-3m Composite
Co ncentration (ppb)
7
6
5
4
OL-1
3
OL-2
2
OL-3
1
0
24-Jun
10-Jul
23-Jul
Date Sampled
Figure 2. Chlorophyll a (ppb) 0-3 meter composite for Otsego Lake, New York, sample sites
OL-1, OL-2, and OL-3 for samples collected 24 June and 10, 23 July 2009.
Table 2. Average chlorophyll a (ppb) 0-3 meter composite for Otsego Lake, New York, sample
sites OL-1, OL-2, and OL-3.
Sample Date
24-Jun
10-Jul
23-Jul
Average
OL-1
6.0
0.4
0.9
2.4
OL-2
5.1
1.0
0.5
2.2
OL-3
5.7
0.8
0.3
2.3
Phytoplankton
Figure 3 illustrates the composition of each sample in terms of the relative abundance of
each of the four taxonomic groups for each sample date and site. Chlorophyta was the dominant
taxon in the community at each site for all sample dates, generally comprising greater than 80%
of algal cells counted (Figure 3, Table 3). Cyanophyta was the second-most common group in
the algal community, comprising over 11% of algal cells on average. Some samples did not
contain individuals from each of the four taxonomic groups. The community composition varied
slightly between sample sites, though a clear pattern was not apparent. Temporal variation in the
community composition was minimal, though on 24 June, cyanophytes and pyrrophytes
comprised a greater portion of the community than on subsequent sample dates (Figure 3, Table
3).
Phytoplankton Community Percent Composition of Taxa
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
24-Jun
10-Jul
23-Jul
24-Jun
10-Jul
OL-1
Chlorophyta
23-Jul
24-Jun
OL-2
Cyanophyta
Pyrrophyta
10-Jul
23-Jul
OL-3
Chrysophyta
Figure 3. Composition of four different algal groups; Chlorophyta, Cyanophyta, Pyrrophyta and
Chrysophyta for a 5ml, 0-3meter depth sample for Otsego Lake, sample sites OL-1, OL-2, and
OL-3.
Table 3. Percent composition of four algal groups and the total number of organisms counted in
5 mL of concentrate; Chlorophyta, Cyanophyta, Pyrrophyta and Chrysophyta for a 5ml, 0-3meter
depth sample for Otsego Lake, sample sites OL-1, OL-2, and OL-3.
Date Sampled
Chlorophyta
Cyanophyta
Pyrrophyta
Chrysophyta
No. of Organisms
Counted
OL-1
OL-2
OL-3
24-Jun 10-Jul 23-Jul 24-Jun 10-Jul 23-Jul 24-Jun 10-Jul 23-Jul
78.5
94.2
97.6
90.4
88.6
96.8
83.8
99.0
97.3
13.8
4.9
2.4
5.8
9.0
1.9
8.1
0.3
1.8
7.7
1.0
0.0
3.8
1.8
1.3
8.1
0.6
0.9
0.0
0.0
0.0
0.0
0.6
0.0
0.0
0.1
0.0
65
411
124
52
167
158
37
707
112
Historical Comparison
As described and summarized in The State of Otsego Lake (Harman et al. 1997), various
studies of the phytoplankton community have been conducted between 1935 and 1996, including
both taxonomic surveys and chlorophyll a analyses. The current mid-summer community is
dominated by chlorophytes. Cyanophytes are consistently present in the community, but at their
greatest relative abundance comprised less than 20% of algal cells. Table 4 presents historical
and current percent composition of phytoplankton taxa, allowing for qualitative comparisons
between the current mid-summer community composition and those observed for the entire
period of summer stratification (May – Sept.) in 1976 and 1993. At first glance, the composition
documented in 2009 suggests a major shift in community composition, with chlorophytes
comprising greater than 90% of algal cells counted; however, 2009 sampling dates only represent
June and July conditions, and thus provide a mid-summer snap-shot of the community. The
results observed in 2009 are consistent with previously-documented timelines of seasonal
changes in community composition (Harman et al. 1997). It is likely that the percent composition
of taxa would differ substantially with a greater number of sampling dates, as chrysophytes
(diatoms) generally dominate early in the season and cyanophytes become more prevalent later
(Harman et al. 1997).
Table 4. Average percent composition of phytoplankton taxa in the water column during summer
stratification in 1976 and 1993 and in June/July 2009 (modified from Harman et al. 1997).
Group
Bacillariophyceae
Chrysophyceae
Chlorophyta
Cyanophyta
Cryptophyce ae
Pyrrophyta
1976
43
7
12
7
15
16
1993
9
31
60
-
2009
0.1
92
5
3
CONCLUSIONS
Samples containing the highest chlorophyll a concentration and phytoplankton count
were not strongly correlated. This demonstrates that chlorophyll a concentration and
phytoplankton abundance may not always be directly related. There was also no apparent
relationship between the concentrations of chlorophyll a and taxonomic composition of the
phytoplankton community. Historical changes in the community could not be quantified. Further
research may provide additional insights into short-term community dynamics and historical
changes.
REFERENCES
Albright, M.F., H.A. Waterfied. 2009. Otsego Lake limnological monitoring, 2008. In 41st Ann.
Rept. (2008). SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta.
APHA, AWWA, WPCF. 1989. Standard methods for the examination of water and wastewater, 17th
ed. American Public Health Association. Washington DC.
Dillard, G.E. 1999. Common freshwater algae of the United States. Berlin: Gebruder Borntraeger.
Harman, W.N., L.P. Sohoacki, M.F. Albright, D.L. Rosen. 1997. The state of Otsego Lake 19361996. Occasional Paper #30, SUNY Oneonta Biol. Fld. Sta., SUNY Oneonta.
Prescott, G. W. 1954. The fresh-water algae. WM. C. Brown Company. Dubuque.
Sheath, R.G., J.D. Wehr. 2003. Introduction to freshwater algae. In: Freshwater algae of North
America. Elsevier. San Diego.
Stevenson, R.J., J.P. Smol. 2003. Use of algae in environmental assessments. In: Wehr, J.D. and
R.G. Sheath (Ed.). Freshwater Algae of North America. Elsevier. San Diego.
Tressler,W.L. and R. Bere. 1936. A limnological study of some of the lakes in the Delaware and
Susquehanna watersheds. In A biological survey of the Delaware and Susquehanna
watersheds. NYS Dept. Environ. Conserv. Albany, NY.
Welschmyer, N.A. 1994. Fluorometric analysis of chlorophyll a in the presence of chlorophyll b
and pheopigments. Limnol. Oceanogr. 39:1985-1992.