RECENT CHANGES IN
THE PHYTOPLANKTON OF
LAKES ERIE AND ONTARIO
April, 1980
Ministry
of the
Environment
The Honourable
Harry C. Parrott, D.D.S.,
Minister
Graham W. S. Scott, Q.C.,
Deputy Minister
RECENT CHANGES IN THE PHYTOPLANKTON
OF LAKES ERIE AND ONTARIO
Presented at
the Second Conference on Changes in the Biota of Lakes Erie and Ontario.
March 10-11, 1980 Buffalo, New York
Kenneth H. Nicholls
Limnology and Toxicity Section
Ontario Ministry of the Environment
P.O. Box 213, Rexdale, Ontario
April, 1980
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Preface
This report represents the expanded text of an invited paper presented at the
Second Conference on Changes in the Biota of Lakes Erie and Ontario held at State
University College, Buffalo, New York on March 10-11, 1980. Two other speakers
summarized the recent changes and present status of zooplankton and fish
communities in the Lower Lakes. The Conference was convened by the Great Lakes
Laboratory of the State University and included a thorough discussion of the future
direction of biological research and monitoring programmes in the Great Lakes. The
proceedings of the Conference, including transcripts of the discussions will be published
as a Bulletin of the Buffalo Society of Natural Sciences during 1980 or early 1981.
-i-
Summary
A review of phytoplankton data collected over the past 10-15 years on Lakes
Erie and Ontario is presented.
Although the phytoplankton communities of the open waters of both lakes are
adequately described for the 1970-1973 period, very little comparable data were
collected either previously or more recently so that data for trend analysis are not
available for the open lake waters.
Municipal water intake records at Cleveland (Ohio) and at Kingsville (Ontario)
show significant declines in Lake Erie phytoplankton densities during the early 1970's
and probably reflect the decreased localized inputs of phosphorus resulting from
legislation limiting the phosphorus content of laundry detergents. Some care is needed
in interpretation of Lake Erie intake records since apparent trends in some species are
related to changes in lake levels and to discharge from nearby rivers.
Lake Ontario phytoplankton can be distinguished as separate inshore and
offshore communities, especially during spring and early summer, owing perhaps to
the development of the thermal bar. The seasonal changes and species composition
of Lake Ontario phytoplankton indicates a "perturbed" state, atypical of a lake the size
and depth of Lake Ontario. Changes in species composition which occurred in the lake's
outflow over the past decade (monitored weekly in Brockville water treatment plant
samples) are not completely understood, but may be related to changes in the
structure of the lake's food chain (recent changes have also occurred in the
zooplankton and fish communities of Lake Ontario).
Significant declines (50-60%) in phytoplankton density in the inner Bay of
Quinte resulted after implementation of a phosphorus control programme and a
reduction of about 60% in phosphorus loading from municipal sewage treatment
plants.
-ii-
Most importantly, the improvement in the Bay of Quinte was experienced in the
operation of the Belleville water treatment plant where fewer algal related problems
of tastes and odours were encountered. Also, microstrainers in the plant were in use
only for a few weeks during the two years following reduced phosphorus loadings
compared with annual operating times of 4-5 months prior to reductions in phosphorus
loading.
A list of several "new arrivals" (marine invaders?) is presented and the known
distribution of these species is discussed. With the increasing content in the Lower
Lakes of conservative elements such as sodium and chloride, it is reasonable to expect
that some marine species with euryhaline or halophilic requirements for growth are
finding suitable habitat especially in localized nearshore and harbour areas.
-iii-
Acknowledgements
The following people contributed data or other information which has been useful
in the development of this report: V. Frederick, M. Griffiths, D. Haffner, Y. Hamdy, C.
Herdendorf, G. Hopkins, J. Kubus, D. Larson, D. Middleton, E. Stoermer and A.
Winklhofer. Phytoplankton data reported for several Ontario locations are based mainly
on laboratory analyses by J. Beaver, E. Carney, F. Forbes, L. Heintsch, C. Lea, L.
Nakamoto and D. Standen. R. Winson and A. Strileski prepared some of the figures
and J. Kurdel typed the manuscript. Finally, I would like to thank the Conference
organizers for their invitation to participate.
-iv-
Introduction
The lower Great Lakes region is dominated by several major urban and industrial
centres which use Lakes Erie and Ontario as sources of domestic and industrial water
supply, as sites for disposal of treated and untreated municipal sewage and industrial
effluent and for other uses ranging from recreational pursuits to commercial fishing to
transportation. The economy of the entire region depends heavily on the multipurpose
use of the Lower Lakes.
The rapid growth of large cities such as Detroit, Toledo, Cleveland, Toronto,
Hamilton, Buffalo and Rochester with populations ranging between 0.3 and 2.2 million
people has undoubtedly led to changes in the water chemistry and biota of the Lakes
Erie and Ontario during the past century (Sweeney 1969, 1971).
The present state of population densities and species composition of the
phytoplankton of the Great Lakes is to a large degree related to the past and current
loadings of materials from urban, industrial and agricultural drainage. Most of the
geographical differences in algal species composition in the Great Lakes can be related
to differences in the inputs of nutrients such as nitrogen and phosphorus and
conservative elements such as sodium and chloride (Stoermer 1978).
To slow the rate of eutrophication, control of phosphorus inputs to the Lower
Lakes was recommended (Int. L. Erie and L. Ontario - St. Lawrence R. Wat. Poll.
Boards, 1969; Vallentyne et al., 1970) and the International Joint Commission (1972)
established target loads for phosphorus based on maximum allowable total phosphorus
concentrations in treated effluent of 1 mg P/L. Legislation to control the phosphorus
content of laundry detergents was introduced in the early 1970's in Ontario and parts
of the United States (Sweeney 1973; Nicholls et al., 1980) and together with the
phosphorus removal programme at sewage treatment plants, has apparently resulted
in a reduction in the phosphorus loading to parts of Lakes Erie and Ontario. For
example, average phosphorus loadings from the Detroit River decreased from about
-1-
75 metric tons/day during the 1968-70 period to about 35 metric tons/day by the early
1970's and were reduced further during 1978 and 1979 (Great Lakes Water Qual.
Board, 1979). Similarly, treatment plants serving Metro Toronto and adjacent regions
have removed more than 2500 tons of phosphorus per year since implementation of
the P control programme. Results of Lake Ontario monitoring have shown a decline in
off-shore springtime concentrations of about 12% and as much as 40% in the
nearshore area 30 km east and west of Metro Toronto.
The well-documented changes which occurred between the 1930's and the
1960's in the phytoplankton of Lakes Erie and Ontario (Verduin, 1964; Davis, 1964;
Schenk and Thompson, 1965; Hohn, 1969) provided clear evidence for the accelerated
eutrophication of these lakes. It is therefore important that the phytoplankton of these
Great Lakes continue to be monitored so that the effectiveness of remedial
programmes such as the phosphorus control programme can he evaluated.
I.
Lake Erie
Lake Erie has been the most thoroughly studied of all the Laurentian Great Lakes
owing to early diagnosis by limnologists of its water quality problems as they related
to excessive production of algae (Burkholder 1929; Gottschall 1930). Reviews of
available information on the phytoplankton of L. Erie were presented by Davis (1969)
and by Prantner et al., (1974). The phytoplankton of the shallow western basin
(especially of the Bass Islands area) has been more thoroughly studied than any other
region of the lake. Consequently, a valuable record of the changes in Lake Erie
phytoplankton, especially the diatoms, is available for a period spanning several
decades (Hohn 1969). Taft and Taft (1971) have provided a much needed
comprehensive compilation of the taxonomy of algae (excluding diatoms) of Lake Erie's
western basin.
-2-
Of the several diatom species which increased in importance (Table 1), most are
well recognized as eutrophic indicators (e.g. Coscinodiscus rothii, Stephanodiscus
binderanus and S. tenuis). The increased importance of the eutrophic diatom species
was accompanied by a decrease in importance of several other species, notably the
more meso-oligotrophic species Cyclotella stelligera and Rhizosolenia eriensis
(Table 1).
During the period of 1960-1970, changes apparently continued although those
species such as Fragilaria crotonensis and Coscinodiscus rothii which were abundant
during the 1950's, were still very important during the 1960's (Hohn 1969; Munawar
& Munawar 1976). Two eutrophic Stephanodiscus species (S. hantzschii and S.
niagarae) increased in importance while two others S. alpinus and Fragilaria capucina
appear to have become less important.
Between 1970 and 1980, there is a scarcity of data from the central areas of the
western basin; however, phytoplankton data have been recorded weekly at Kingsville
where a monitoring programme has been in place since 1967 at the Union Water
Treatment Plant. Nicholls et al., (1977, 1980) have related significant declines in
phytoplankton in the Union intake between 1970 and 1976 to decreased phosphorus
loading from the Detroit River.
Phytoplankton density in the Union intake samples averaged about 5000 Areal
Standard Units (A.S.U.)/ml during the 1967-1970 period but declined about 40% to
2900 A.S.U./ml by 1975 (Fig. 1). All classes of algae have declined; however, most of
the decrease in total phytoplankton was accounted for by declines in diatoms which
comprised 65-80% of the total during the 9 year period. During the same period, and
largely as a result of Michigan's detergent legislation, phosphorus loading from the
Detroit River declined from an average of about 78 metric T/day to about 33 metric
T/day by 1975. Phosphorus inputs from the Detroit River continued to decline and by
1978 averaged only about 20 metric T/day (Great Lakes Water Qual. Bd., 1979).
-3-
Table 1.
Changes in the relative importance of western Lake Erie diatoms between approximately 19 30 and 1980.
Increased
Up to 1960
Decreased
Fragilaria capucina Desm.
Asterionella formosa Hass.
F. crotonensis Kitton
Tabellaria fenestrata (Lyngb.) Kütz
Coscinodiscus rothii (Ehr.) Grun.
Melosira ambigua (Grun.) O. Mull.
Stephanodiscus binderanus (Kütz.) Kreig.
Cyclotella stelligera (Cl. and Grun.) V.H.
S. alpinus Hust.
Rhizosolenia eriensis H.L. Sm.
S. tenuis Hust.
Cyclotella meneghiniana Kütz.
Diatoma tenue var. elongatum Lyngb.
1960-1970
1970-1980
S. niagarae Ehr.
F. capucina
S. hantzschii Grun.
S. alpinus
T. fenestrata
D. tenue var. elongatum
Sources of information:
Verduin (1964), Hohn (1969), Munawar and Munawar (1976),
Nicholls et al., (1977, 1980)
-4-
Fig. 1.
Densities of total phytoplankton in samples of Lake Erie "raw" water
collected through the Union Water Treatment Plant intake. Vertical bars
are annual means and dots are four-month moving averages of monthly
means (from Nicholls et al., 1980).
Fig. 2.
Average densities of total phytoplankton and of Fragilaria in summer and
winter periods (from Nicholls et al., 1980) in Union intake samples.
-5-
Gladish (1978) reported results of a phytoplankton study at a location near Point
Pelee sampled between June 1975 and September 1976. He found an average
phytoplankton biomass of 2.5 mm3/L which was 38% lower than the average of 4.0
determined by M. Munawar (unpublished) for the same location in 1970. Unfortunately
the 1970 survey included only seven samples collected between April and December
and it couldn't be shown that the difference between the means of the two studies was
statistically significant. It is worth noting that the decline shown by the Union intake
data over exactly the same period was essentially the same at 41%. The overall
decline observed in the Union data with 52 samples per year between 1971 and 1975
averaged 10% per year and is highly significant.
Despite the continued reduction in phosphorus inputs to the western basin of
Lake Erie and the continued declines in total P concentration near the north shore,
phytoplankton densities increased again in the Union Intake samples collected since
1976 (Nicholls et al., 1980). The recent increase has been in the summer
phytoplankton only; winter densities in 1977-78 were the lowest on record (Fig. 2).
Furthermore, the recent increase in phytoplankton was attributed to a single species,
Fragilaria crotonensis (Fig. 2). The increases in Fragilaria may have been related to a
change in water level which influenced resuspension of this species. As well, an effect
of the phosphorus control programme may have been the control of diatom growth
during winter and spring resulting in increased availability of silica for growth of
Fragilaria during summer (Nicholls et al., 1980). In regard to the phosphorus control
programme in western Lake Erie, it is significant that "weedy" species of blue-green
and green algae show long term trends which are clearly divided into a pre-1971
period of high density and a post 1971 period of much lower densities (Fig. 3).
In the central basin of Lake Erie, the first clear evidence for rapid eutrophication
was provided by Davis (1964) from Cleveland's Division Ave. Filtration Plant
phytoplankton records (Fig.4 ). Phytoplankton density increased consistently between
1919 and 1963 at a rate of about 40 cells/ml•yr.
-6-
Fig. 3.
Average densities of Scenedesmus spp. in Union intake samples. Vertical
bars are annual means and dots are four-month moving averages of
monthly means (from Nicholls et al., 1980).
-7-
Fig. 4.
Phytoplankton densities in L. Erie samples collected from the Cleveland's
Division Avenue Filtration Plant (from Davis, 1964).
-8-
Other important changes included a lengthening of the periods of the spring and fall
maxima with correspondingly shorter durations of the summer and winter minima
(Davis, 1964). Annual average densities increased about 4-fold between the early
1930's and the early 1960's.
Phytoplankton data collected at the Division Ave. plant between 1968 and 1972
(Reitz 1973) show a drastic reduction in cell densities from those of the late 1950's and
early 1960's (Fig. 5). Densities during March, April and May of 1968 are similar to
those of 1962, but 1969-1972 data show only minor spring peaks and little or no
evidence of a fall peak (Fig. 6). Unfortunately, little information on species composition
is available from the recent Cleveland intake study; however, the cell densities
recorded for the 1970's are similar to those found during the 1930's and are reason for
considerable optimism relating to improvement in nearshore areas of Lake Erie.
The deep eastern basin of Lake Erie was generally ignored by algologists (see
Munawar & Munawar 1976) until about 10-12 years ago. Since then, sampling and
analysis efforts have increased greatly and phytoplankton information is now available
from a number of sources (Fig. 7). Unfortunately, although sampling locations between
these studies coincide closely in many cases, sampling method have differed (Table 2)
so that strict comparisons between years are not possible. Nevertheless, the biomass
values reported are all generally similar in the range 1-3 mm3/L (Fig. 8) and all studies
report similar seasonal distribution of algal species. On average, Cryptomonas and
Rhodomonas species have comprised about 30% of the total phytoplankton cell
volume. Other taxa consistently reported in the results of the eastern basin studies
include spring and fall pulses by Stephanodiscus tenuis and S. niagarae and Peridinium
aciculiferum (Lemm.) Lem. (mainly in the spring) and occasional abundance of the
prymnesiophyte Chrysochromulina parva Lackey.
Evidence for recent changes in the phytoplankton of the eastern basin cannot
be obtained from the data available with the possible exception of the Dunnville water
intake data (Fig. 8). Samples of raw water from the intake located 6 m deep and 0.5
-9-
Fig. 5.
Annual average phytoplankton densities in Lake Erie samples collected
between 1920 and 1972 from the Cleveland's Division Avenue Filtration
Plant (from Davis, 1964; Reitz, 1973).
-10-
Fig. 6.
Seasonal distribution of phytoplankton densities in Lake Erie samples
collected during 1962 and between 1968 and 1972, Cleveland's Division
Avenue Filtration Plant (from Davis, 1964; Reitz, 1973).
-11-
Fig. 7.
Locations of sampling sites in eastern Lake Erie for major phytoplankton
studies undertaken since 1967, by Ontario Ministry of the Environment
(Hopkins & Lea, 1979 and unpublished data), Great Lakes Biolimnology
Lab. (Munawar & Munawar, 1976) and State University College at Buffalo
(V.R. Frederick, personal comm.).
-12-
Fig. 8.
Average (annual or ice-free period) phytoplankton biomass (mm3/L) in
eastern Lake Erie (see Fig. 7).
Table 2.
Summary of sample collection methods used during recent investigations
of phytoplankton of the eastern basin of Lake Erie.
Map Symbol (Fig. 7)
Collection Method
Min. of the Environment
(Ont.) (N. shore 1979)
composite (surface to 2x
Secchi disc visibility
Min. of the Environment
(Ont.) (Nanticoke Study, 1969-78)
composite (surface to 2x
Secchi disc visibility)
S.U.C.B. (1973-76)
1m
G.L.B.L. (1970)
1 m and 5 m (mixed)
Dunnville Water Intake (1967-79)
6 m deep; 0.5 km offshore
-13-
km offshore have been collected weekly or bi-weekly since 1967. There was an
apparent increase during the 1973-76 period which resulted in a doubling of average
annual biomass in relation to the values from the late 1960's and early 1970's. More
recently, algal densities in the Dunnville intake samples returned to levels more typical
of the earlier years (Fig. 8).
This long term trend in phytoplankton densities may be related to nutrient
loading from the adjacent Grand River. Flow data from the Grand River (Fish. & Envir.
Canada, 1969-1978) show a trend which generally parallels the trends in algal density
in the Dunnville intake except for a period of several months during 1975 (Fig. 9). A
preliminary evaluation of available total phosphorus data for the lower Grand River
(Min. Envir. 1973-1978) suggests that trends in phosphorus loading from the Grand
River probably parallel the flow data closely since there has been little year-to-year
change in P concentrations between 1972 and 1977.
Furthermore, there is evidence from river plume tracking using specific
conductance measurements (Ross & Hamdy 1980) that the Grand River discharge
often impinges directly on the north shore water mass serving the Dunnville intake. It
is clear that nutrient concentrations in the Grand River mouth are sufficient to support
algal densities which are several times higher than those found farther offshore
(Fig.10). It is likely, therefore, that trends observed in the Dunnville intake data are
the result of local river influences and may not be typical of a very extensive portion
of the nearshore zone in the eastern basin of the lake.
-14-
Fig. 9.
Discharge of the Grand River (measured at Brantford) and phytoplankton
densities in the Dunnville water intake. The plotted points are 13-point
moving averages of the monthly means.
-15-
Fig. 10.
Mouth of the Grand River, Ontario, showing the locations of three
sampling sites and average biomass and composition of phytoplankton
during the May to November period of 1979 (Ont. Ministry Environ.,
unpubl. data). D, Dunnville intake.
-16-
II.
Lake Ontario
Stoermer et al., (1975) point out that Lake Ontario was the first of the Great
Lakes to experience the intrusions of the white man and his colonial activities of forest
clearing, town and city development and associated sewage and industrial waste
disposal. Also, because of its position in the Great Lakes basin as the last lake in the
system, it has been subjected to much of the "second-hand" pollution from other urban
and industrialized parts of the basin.
There are three large data bases which have to be considered in any assessment
of recent changes in Lake Ontario phytoplankton (Fig. 11). Nalewajko (1966, 1967)
and Sreenivasa and Nalewajko (1975) reported on phytoplankton data from 11
sampling sites in northeastern Lake Ontario collected between April and November of
1965 and from one site off Gibralter Point collected between Jan. 1964 and July 1965.
Munawar & Nauwerck (1971) sampled 32 stations over the whole lake at monthly
intervals between January and December, 1970. Finally, Lake Ontario phytoplankton
was studied during 1972 and 1973 under the auspices of the Lake Ontario IFYGL
Programme ("International Field Year on the Great Lakes") by Stoermer et al., (1975)
at 40-60 sites over the whole lake.
Without a continuous record it is very difficult to evaluate small differences in
the results of these studies in terms of "real" changes with time. Many of the
differences are probably normally occurring year-to-year differences which are
controlled by weather, lake levels, runoff, etc. For example, Stoermer et al., (1975)
noted several differences in the summer phytoplankton populations existing in 1972
and 1973 that were undoubtedly related to the effects of Tropical Storm Agnes which
influenced the local Lake Ontario weather greatly. June of 1972 was the coldest and
wettest on record. Although there is no evidence for a change in the Lake Ontario
phytoplankton over the short period of time that the lake has been studied recently,
it is worth summarizing some of the common findings of these studies which provide
an adequate baseline for comparisons at some future time. All available phytoplankton
-17-
Fig. 11.
Map of Lake Ontario showing locations of sampling sites for major
phytoplankton studies undertaken since 1965.
Fig. 12.
Densities of phytoplankton in weekly samples from the Brockville water
treatment plant (Ont. Min. Environ., unpubl.).
-18-
data suggest that Lake Ontario is a highly disturbed system. From the three years of
whole-lake work done thus far, a consistent and reproducible pattern to the seasonal
succession of phytoplankton is not apparent. Generally, the spring and early summer
phytoplankton is dominated by diatoms (mainly Stephanodiscus tenuis, S. binderanus,
S. hantzschii and Melosira islandica) with important contributions by the green alga
Scenedesmus bicellularis Chod. and several phytoflagellates such as Cryptomonas,
Rhodomonas, Pedinomonas and Chrysochromulina parva. Several species of
chlorococalean algae become important during summer. Blue-green algae seem to be
restricted to late fall and include eight or nine common species of the genera
Aphanizomenon, Gomphosphaeria, Microcystis and Anabaena. Two diatoms, Nitzschia
dissipata (Kütz.) Grun. and Surirella angusta Kütz. are generally regarded as benthic
forms of eutrophic lakes yet both have been reported as winter dominants in Lake
Ontario's plankton.
The phytoplankton assemblages present in Lake Ontario are represented by
many species which are widely recognized as associates of eutrophic and often
halophilic lake states. As well, many oligotrophic diatom species which characterize the
open waters of the upper Great Lakes such as Cyclotella comensis Grun., C. comta
and Melosira distans (Ehr.) Rutz. (Stoermer, 1978) are absent or unimportant in Lake
Ontario. The lake shows drastic seasonal shifts in species composition which are typical
of eutrophic waters and clearly atypical of a lake the size and depth of Lake Ontario
(see, for example, Vollenweider et al., 1974; Stoermer & Yang, 1969).
Very large differences are now known for phytoplankton of nearshore Lake
Ontario and the open lake. Nalawajko (1966) showed that the dominant species in
surface waters near Gibralter Point between January 1964 and July 1965 were
Stephanodiscus tenuis, Melosira islandica and Diatoma tenue var. elongatum.
Nearshore phytoplankton densities were 2-3 times higher than at offshore sampling
stations (>10 km) where Asterionella formosa replaced S. tenuis as a dominant. Most
of the great inshore-offshore differences can be related to the effects of the thermal
bar which develops within a 1-10 km distance from shore during spring and early
-19-
summer and effectively isolates the nearshore waters with their higher nutrient
contents from the colder offshore waters. Munawar & Munawar (1975) showed that
springtime diatom populations developing within the thermal bar may be limited by
silica depletion.
Several older studies of the nearshore Lake Ontario phytoplankton have been
completed (see Stoermer et al., 1975 for a review) but only the data from the Toronto
Island Filtration Plant compiled by Schenk & Thompson (1965) provide any evidence
for long term change. The Toronto intake data showed that phytoplankton densities
approximately doubled between 1923 and 1954. Unfortunately these records cannot
be updated because the Island Filtration Plant has been used only intermittently
(mainly during summer) during the past 20 years. However, we have begun an
examination of the plankton records at other Toronto area water treatment plants in
co-operation with their staff so that the earlier records might be supplemented by more
recent data from other nearby locations.
Although much of the early investigation of nearshore Lake Ontario
phytoplankton can serve as valuable historical information (Burkholder & Tressler,
1932; Tressler & Austin, 1940) the available evidence suggest that changes in the
nearshore zone had taken place long before these early studies. Mackay (1930) and
Neil & Owen (1964) have described extensive growth of Cladophora and localized
polluted areas of Lake Ontario which existed before the 1930's. It is therefore probable
that many of the nearshore phytoplankton associations which we associate with
present day eutrophic conditions in Lake Ontario may have existed in the early part of
this century. In this regard, it is significant that studies done nearly 20 years after
those done by Tucker (1948) in 1945-46 in the Bay of Quinte were not able to detect
any significant change in the phytoplankton (McCombie 1967). We should not infer
from these conclusions that nearshore Lake Ontario has always been eutrophic.
Sreenivasa & Duthie (1975) reported the dominant eutrophic diatom Stephanodiscus
tenuis as common only in the upper 10 cm of Lake Ontario sediment cores, suggesting
that it was not always indigenous to the lake.
-20-
Lake Ontario's phytoplankton is probably controlled to a large degree by nutrient
supply; evidence that phosphorus in Lake Ontario is the "controlling" element is
extensive and widely accepted (Thomann et al., 1977; Schelske, 1979; Scavia, 1979).
Recent evidence (Great Lakes Water Quality Bd. 1979; Dobson and Chapra, 1980)
suggests that phosphorus concentrations are declining in Lake Ontario. The rate of
decline of springtime lake-wide average total phosphorus concentrations is about 1 µg
P/L!yr (1972-1978). At this rate it may take a few more years yet before changes are
noticed in the phytoplankton of the open lake.
The Ontario Ministry of the Environment has been monitoring phytoplankton in
the outflow of Lake Ontario at Brockville in the St. Lawrence River since 1967
(unpublished; see also Michalski 1968). The composition has appeared typical of a
"blend" of Lake Ontario nearshore and open lake water with the diatoms S. tenuis, S.
binderanus, A. formosa and M. islandica all very common in the samples. Springtime
peaks in biomass have occurred consistently every year since 1967 (Fig. 12); however,
there is no clear evidence for a longer term change which might be related to the
phosphorus control programme.
There have been some dramatic changes in the composition of phytoplankton
in the Brockville samples. Tabellaria (mainly T. fenestrate) has become less and less
abundant (Fig. 13). This species was absent for only 10-12 weeks of the year in the
late 1960's but by 1978 it was absent for 40 weeks of the year. The same trend is
evident in records kept much farther down the St. Lawrence River at Cornwall where
annual average densities of Tabellaria have declined about 80% over the past 12 years
(Fig. 14). Another important change we have observed in the Brockville samples is a
dramatic increase in the importance of Cryptophyceae. Rhodomonas and Cryptomonas
species constituted only 5% of the total phytoplankton biomass in the late 1960's but
had increased to over 30% by 1978 (Fig. 15). I do not have explanations for these
changes, but they support the findings reported during the early 1970's which suggest
that Lake Ontario phytoplankton is very unstable.
-21-
Fig. 13.
The number of weeks showing densities of Tabellaria spp. continuously
less than 5 Areal Standard Units/ ml in Brockville water intake samples.
-22-
Fig. 14.
The number of weeks showing densities of Tabellaria spp. continuously
less than 5 Areal Standard Units/ ml and annual average densities from
1967 to 1978 at the Cornwall water treatment plant in the St. Lawrence
River (Ont. Min. Envir., unpubl.).
-23-
Fig. 15.
Increases in Cryptophyceae in Brockville water treatment plant samples
collected weekly between 1967 and 1978 (Ont. Min. Envir., unpubl.).
-24-
In Lake Ontario's Bay of Quinte, the response to phosphorus loading controls has
been very rapid and dramatic. The Bay of Quinte has been monitored at several
locations between Lake Ontario and the Trent River as part of "Project Quinte" since
1972. It has become known as perhaps the most eutrophic area of the Canadian Great
Lakes (Johnson & Owen, 1971; Nicholls & Carney 1979). Prior to 1978, total
phosphorus inputs to the Bay of Quinte averaged about 150 kg P/day but were reduced
during 1978 by more than 50%. Although no noticeable changes in phytoplankton
biomass and composition were observed in the outer bay (Fig. 16), there has been a
dramatic decline in total biomass in the inner bay, especially in diatoms and blue-green
algae (Figs. 16, 17) which has coincided with a marked decrease in total phosphorus
concentrations but with increases in silica and nitrate (Fig. 17).
The accumulation of these nutrients has undoubtedly occurred because growth
of the algae in the Bay of Quinte is phosphorus controlled. In many ways the most
significant finding is contained in the records of the Belleville water treatment plant.
Post phosphorus control densities of algae in samples collected weekly in the "raw"
water intake were 50-60% lower than those recorded prior to 1978 (Fig. 17). Most
importantly, there were clear benefits to water treatment plant operation. Belleville
water treatment plant data show much lower turbidity and threshold odour values since
the phosphorus control programme was implemented. Microstrainers in the treatment
plant were in use only for a few weeks during 1978 and 1979, whereas prior to 1978,
micro-strainers were necessary for 4-5 months of the year.
It is especially important that declines in algal density and changes in species
composition which occur as a result of the phosphorus control programme be
translated into concepts (such as improved water treatment plant operation, a fishery
based on a more efficiently functioning food chain and clearer water for recreation and
aesthetic enjoyment) which the public recognizes as beneficial to society and the Great
Lakes ecosystem.
-25-
Fig. 16.
Average ice-free period biomass and composition of phytoplankton in the
inner Bay of Quinte (Station B) and the outer Bay of Quinte near Lake
Ontario (Station C) before and after implementation of a phosphorus
removal programme at local sewage treatment plants (Ont. Min. Envir.,
unpubl.).
-26-
Fig. 17.
Ice-free period averages of several limnological parameters measured in
the inner Bay of Quinte (Station B) before and after implementation of
the phosphorus control programme. Also shown are the average
phytoplankton densities recorded in samples from the Belleville water
treatment plant intake (D. Middleton, personal comm.).
-27-
III.
"Marine Invaders"??
A number of new arrivals have been reported recently for the phytoplankton of
the Great Lakes. It is not clear whether these species are really recent invaders or if
they have been long-time residents and have been overlooked in earlier studies
because of their scarcity and often restricted and localized distribution. Many are very
small and fragile forms and can only be detected by careful laboratory practice and
techniques such as electron microscopy which have not been used routinely in Great
Lakes phytoplankton studies (Stoermer & Sicko-Goad, 1977). On the other hand, most
of the so-called "new arrivals" show definite halophilic tendencies in their known
distribution in other parts of the world. It is conceivable that the increase in
concentration of conservative elements in the Lower Great Lakes (Chawla 1971) has
created an environment, especially in inshore and harbour areas, which would be more
suitable for growth of halophilic species than the more dilute waters of the Upper Great
Lakes. Certainly, the opportunity for invasion of the Great Lakes by marine or estuarine
species is very great given the large amounts of seawater ballast which are discharged
every year during the shipping season on the Great Lakes. A brief outline of the
taxonomy and known distribution of the most important "new arrivals" is given below.
Cyclotella atomus Hustedt
C. atomus is known from several rivers and lakes in Germany, Java, Sumatra
and South Africa and coastal Scandanavian waters with salinities ranging up to 30. It
has been found recently in five rivers in the United States (Hohn & Hellerman 1963;
Lowe 1975). Belcher & Swale (1978) reported it from England for the first time in
collections made in 1977 from the Trent and Thames Rivers at salinities of about 1%.
The first report from the Great Lakes was by Sreenivasa & Duthie (1975), but it may
have been a long-time resident because they reported it as very common in bottom
sediments of Lake Ontario. Sreenivasa & Nalewajko (1975) found it in samples
collected in 1965 in N.E. Lake Ontario. More recent reports from Lakes Erie and Ontario
have been made by Stoermer (1978), Stoermer & Kreis (1978) and Nicholls & Carney
-28-
(1979).
Stephanodiscus subtilis (Van Goor) A. Cl.
basionym: Melosira subtilis Van Goor
This species is known from several rivers in Holland, weakly saline waters near
Stockholm as well as Lake Malaren (Sweden) and the North Sea. A report of this
species from the Volga River in the Soviet Union (Kuz'min et al., 1970) seems to be of
Skeletonema subsalsum (A. Cleve) Bethge and not S. subtilis and hence raises some
doubts about the validity of other reports of S. subtilis (Hasle & Evensen, 1976).
Stoermer et al., (1975) recorded S. subtilis from Lake Ontario for the first time from
collections made in 1972. Its seasonal distribution in Lake Ontario was quite striking
(Fig. 18) with highest cell densities found in the southeastern portion of the lake during
mid-May. By mid-June, these populations had declined and northern half of the lake
showed highest densities (Stoermer et al., 1975). The first report of S. subtilis from
Lake Erie is Stoermer (1978).
Skeletonema subsalsum (A. Cleve) Bethge
basionym: Melosira subsalsa Cleve-Euler
S. subsalsum has been found in coastal areas of Scandanavia and the Baltic,
as well as from the Sea of Azon, the Volga River (U.S.S.R.) and the Wumme River
(Germany). It was reported for the first time from the Great Lakes by Hasle & Evensen
(1975) from Sandusky Bay, Lake Erie and from Lake Ontario by Stoermer (1978).
Recent reports of this species from Lake Erie's central basin may have included S.
potamos (Reuter, 1979). The species is clearly halophilic and likely an indicator of
eutrophy as well (Hasle & Evensen, 1976).
-29-
Fig. 18.
Distribution of Stephanodiscus subtilis in Lake Ontario during spring and
early summer (from Stoermer et al., 1975 ; cells/ml).
-30-
Skeletonema potamos (Weber) Halse
basionym: Microsiphona potamos Weber
Synonym: Stephanodiscus subsalsus (A. Cleve) Hust.
S. potamos was first described as a new species of the new genus Microsiphona
in 1970 from Ohio. It is known from Europe and several North American rivers. In the
lower Great Lakes it has been found in Lake Erie's Sandusky Bay (Hasle & Evensen,
1976) and in Lake Ontario (Stoermer, 1978) including the Bay of Quinte (Nicholls &
Carney, 1979). It has been grown in cultures over the full range of salinity
representing freshwater to seawater.
Thalassiosira fluviatilis Hustedt
T. fluviatilis is a well known brackish water and marine species and is very
common in estuaries in Europe. In cultures, it thrives at salinities ranging from 5%. to
full strength seawater (Belcher and Swale, 1977). It was first reported for the Lower
Lakes by Wujek (1967) who found it in western Lake Erie.
T. pseudonana Hasle & Heimdal
This was described as a new species from brackish and marine localities in
Norway (Hasle & Heimdal, 1970). Lowe & Busch (1975) reported it from Ohio and
Stoermer (1978) recorded it from both Lakes Erie and Ontario.
Bangia atropurpurea (Roth) A. (a benthic species, not planktonic)
The spread of B. atropurpurea in the Great Lakes since it was first discovered
in Buffalo Harbor in 1964 has been reviewed by Lin & Blum (1977). It is now widely
distributed in Lakes Erie, Ontario and Michigan and at least one localized area in Lake
Huron. Its euryhaline tolerances may be compounded by unusually high requirements
for some trace metals such as zinc (Lin & Blum 1977).
-31-
"Potamodiscus kalbei" Gerloff
P. kalbei was described as a small centric diatom in 1968 from two essentially
freshwater sites in Germany but it was associated with a few other halophilic species.
Since then it has been found in several coastal marine environments and has
apparently worldwide distribution. The North American localities include Arctic Canada,
Narragansett Bay (Rhode Island) the Gulf of Mexico near Texas, Yaquina Bay (Oregon)
and California's Monterey Bay. It is also known from Sandusky Bay, Lake Erie (Gaarder
et al, 1976) and I discovered it in a sample collected from the north shore of Lake Erie
in 1979. However, "P. kalbei" is not a diatom; it is a siliceous scale which, with many
other scales, form a covering around the protoplast of the heliozoan Pinaciophora
fluviatilis Greef (Thomsen, 1978).
-32-
Appendix A.
I.
Notes on Methods
Field Methods
Several different methods of sample collection are associated with the results
of phytoplankton investigations reported in this paper. There are data available now
to show that surface water samples from both lakes Erie and Ontario may not sample
the bulk of the phytoplankton community which is often located at considerable depth
below the lake surface (Figs.19, 20). Similar vertical distributions are known for the
upper Great Lakes (Watson et al, 1975; Brooks & Torke, 1977).
The implications of this marked vertical stratification are serious when attempts
are made to compare data sets which were not derived from samples collected in the
same way. Even within the framework of a single investigation it is difficult to evaluate
seasonal dynamics of phytoplankton species if surface water samples only are
analyzed. Apparent changes over time in population structure in the surface waters
may in reality represent a vertical redistribution of some of the components of the
phytoplankton community in response to, for example, a changing light or temperature
regime or to physical mixing of the water column as may occur during and after severe
weather. More useful data can be obtained by collecting samples at intervals through
a depth corresponding to the euphotic zone which can usually be estimated quickly in
the field with a Secchi disc (2-3X the Secchi-disc visibility) or more accurately if needed
with a submersible light meter.
Laboratory capacity and time may not allow analyses of all samples collected in
the vertical profiles; in which case samples can be pooled to represent the entire water
column or portions of it such as the euphotic zone or epilimnetic and metalimnetic
zones. As an alternative to point source collection of samples at intervals through a
vertical water column, there are compositing sampling devices available (Lund & Talling
1957; Schroeder 1969).
-33-
Fig. 19.
Vertical distribution of phytoplankton in eastern Lake Erie during early
August, 1976 (V.R. Frederick, S.U.C.E., unpublished).
Fig. 20.
Vertical distribution of phytoplankton in Lake Ontario near Toronto, July,
1978 (Ont. Min. Environ., unpubl.).
-34-
Clearly, the results obtained from deepwater municipal water intakes in the
Great Lakes cannot be related over the short term (one or two years) to results of
surface water phytoplankton analyses for the reasons outlined above. Phytoplankton
data from water intakes are only of value if gathered over a period of several years for
the purpose of trend analyses. The original purpose of these data were of course for
quite different purposes relating to the evaluation of treatment plant function and plant
processes such as the clogging of sand filter beds, the frequency of filter backwashing
and the early detection and control of tastes and odours introduced by algae in the raw
water supply.
Nevertheless, data from certain intakes have been valuable for assessment of
long term trends in nearshore water quality (Davis, 1964; Schenk & Thompson, 1965;
Nicholls et al., 1977). Some care is needed in interpreting these data should lake levels
fluctuate or if optical qualities of the lakewater change (as for example if local river silt
and nutrient loads are controlled, improved light penetration could result in an increase
in some deep water phytoplankton populations - an increase which would likely be
noticed in intake samples but which would seem to contradict the declines in biomass
which would probably be measured in surface water samples (as a result of decreased
nutrient supply to the surface waters).
Changing lake levels can lead to considerable changes in the average
temperature and light intensity at the level of an intake located a fixed height above
the lake bottom (Figs. 21, 22). These changes may mean that certain populations in
the phytoplankton which normally stratify at a certain depth according to their light and
temperature requirements may be sampled at some times by the intake but not at
others depending on the lake level. For example in Lake Erie's western basin, there
seems to be a trend to increasing densities of dinoflagellates in recent years. However,
the long term (12 year) annual averages of these organisms is highly correlated with
lake level (Fig. 23) and suggests that the intake may be sampling the depth preferred
by these free swimming forms only under certain conditions of lake level.
-35-
Figs. 21,22.
Illustrations showing the changes in optical and temperature
characteristics of water sampled by an intake in a fixed position
with changes in lake level.
-36-
Fig. 23.
Correlation between annual mean total Dinophyceae and lake level. Line
"a" includes a very high density of Ceratium hirundinella in a single
August sample during 1970. The correlation is improved considerably (r
= -0.87; p <0.01) if this value is not included (line "b") (from Nicholls et
al., 1980).
-37-
II.
Laboratory Methods
Laboratory methods for phytoplankton analyses in Great Lakes studies have
generally followed two approaches, those using the compound microscope and those
using an inverted microscope. No single method by itself seems to be completely
satisfactory, rather a combination of tools and techniques probably works best (Fig.
24).
Most studies have used Lugol's solution (IKI and glacial acetic acid) for field
fixation immediately after collection, although other fixatives such as cold
glutaraldehyde are probably as effective. Those studies using the compound
microscope fall into three categories depending on techniques for concentration. Those
that employ sand filtration techniques as outlined in "Standard Methods" risk losing a
large portion of the very small forms. Some Great Lakes laboratories used a filtration
technique to trap the algae on membrane filters which are later cleared and mounted
on slides. Nothing is lost by this technique and with appropriate treatment the slide
then serves as a permanent record. Some disadvantages include damage to some
fragile forms and a certain loss of investigative flexibility in that the specimens are in
fixed positions and cannot be manipulated for measurement or viewing of important
taxonomic features. Use of parallel wet samples seems necessary if the millipore
filtration method is to be fully exploited.
A concentration technique which involves sedimentation in Lugol's solution is
very effective in retaining all algal forms and has an added advantage in permitting a
wet sample to be archived in concentrated form for future reference.
The use of a Sedgwick-Rafter counting cell precludes use of microscope
objectives greater than 20x because of the shorter focal length of higher power
objectives and the great depth of the counting cell. This problem is overcome with the
inverted microscope with which oil immersion objectives can be used if necessary. The
Sedgwick-Rafter cell is satisfactory for counting all but the very small and delicate
-38-
Fig. 24.
Pictorial review of sample fixation, concentration and enumeration
procedures and comparison of two phytoplankton "counts" expressed as
cell numbers, cell volume and Areal Standard Units.
-39-
forms which can be counted in a parallel count on a conventional (slide and cover
glass) wet or dry mount with oil immersion objectives. At least one of the large forms
which is counted in the Sedgwick-Rafter cell must be recounted in the conventional
slide in order to relate the proportional counts of the small forms to "real numbers".
Differential interference optics or some stains such as methylene blue or Jensen's stain
(Nicholls,
1978)
are
most
effective
for
identifying
many
of
the
delicate
semi-transparent forms (eg. Chrysolykos spp.) which would normally not be detected
in a Sedgwick-Rafter cell with a 20x objective. None of the above methods alone will
solve all problems relating to the identification of several of the Chrysophyceae in
particular for which living reference samples and often certain life history stages in
such as statospores or reproductive states are necessary for species identification.
The statistics of enumeration and the levels of counting intensity needed to
achieve certain levels of precision have been detailed by Lund et al (1958), McAlice
(1971), Willen (1976) and Hobro & Willen (1977) and need not be discussed further
here.
Great Lakes studies have reported phytoplankton data in three ways: cell
numbers, cell volume and some standard unit count such as Areal Standard Units. All
have their uses. Cell numbers are reasonable units to use to describe the dynamics or
seasonal fluctuations of individual taxa (e.g. Stoermer et al., 1975). Cell volume
estimates are useful for relating to other ecosystem parameters. If a specific gravity
of 1.0 is assumed for planktonic cells, then cell volume can be expressed as weight or
mass which can be easily related to other limnological measurements expressed as
weight such as organic carbon, nutrient and pigment concentrations (Nicholls & Dillon,
1978). The accuracy of cell volume estimates depends largely on the accuracy of cell
measurements and the approximation of algal shapes to geometric solids for which
formulae are known for determining volume. Considerable error can be introduced by
assuming standard sizes or by inaccurate measurements (Sicko-Goad et al., 1977).
The Areal Standard Unit expression of phytoplankton density originated in
-40-
waterworks practice where the relationship of algal density to clogging of filters is best
defined in areal terms. One A.S.U. is an area of algal material equivalent to 400 µm2.
The use of these units in some Great Lakes water intake monitoring programmes
(Nicholls et al., 1977) has been continued so that the historical value of long term
records is not jeopardized. It is useful to be able to relate Areal Standard Units to
biovolume. The relationship between A.S.U. and volume is well defined for common
geometric shapes (Fig. 25) and varies with size (e.g. the diameter of spheres or
cylinders). The relationship between total cell volume and algal density expressed as
Areal Standard Units is well defined for 13 lakes in Ontario (Fig. 26). The equation
(A.S.U./ml = 476 mm3/L - 55) derived from this relationship provides a convenient
method for converting average values of one unit to the other. Caution should be used,
however, since the ratio of A.S.U.-to-volume depends on cell size and hence on the
species composition.
Total cell volume and Areal Standard Units are both more meaningful units than
cell numbers for expressions of the total phytoplankton community. Changes in total
cell numbers do not account for changes in cell size of the components of the total
community. Clearly, the interpretation of a total cell number of 104 cells/ml would be
different if most of the cells were Ceratium than if most were Rhodomonas (Fig. 24).
-41-
Fig. 25.
The A.S.U.-to-volume ratio for two common geometric shapes.
Fig. 26.
The relationship between average phytoplankton cell volume and Areal
Standard Units in samples collected from 13 Ontario lakes.
-42-
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