United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
Research and Development
EPA-600/S3-83-091 Dec. 1983
Project  Summary
Phytoplankton  Abundance,
Species  Distribution,  and
Community  Structure in
Saginaw Bay  and  Southern
Lake  Huron  in  1980

E.F. Stoermer, R.G. Kreis, Jr. E.G. Theriot, and T.B. Ladewski
  Summarized herein are studies con-
ducted during 1980 to assess the
effects of reductions in phosphorus
loading to Saginaw Bay on phytoplank-
ton in the bay and the adjacent waters
of Lake Huron. Quantitative estimates
of phytoplankton abundance were
developed from  an  array of stations
sampled during  the ice-free season.
Distribution and abundance of major
species and multivariate  statistical
representations of associations were
compared to similar data collected
during 1974, prior to phosphorus
loading reductions. Results show a
substantial reduction in the abundance
and range of distribution of eutrophica-
tion tolerant and potentially nuisance-
producing phytoplankton populations
in Saginaw Bay and reduced export of
such populations to the  main Lake
Huron system.
  This Project Summary was developed
by EPA's Environmental Research
Laboratory. Duluth, MN, to announce
key findings of the research project that
is fully documented in separate reports
(see Project Report ordering information
at back).

Objective and Scope
  The primary objective of this investigation
was to determine the effect of phosphorus
loading reductions on phytoplankton
communities in the study area. Secondary
objectives include determination of
regions of biological similarity, which
could furnish a rational basis for segmen-
tation of ecosystem models, and provision
of a reliable biological data base to assess
long-term changes  in the Lake Huron
ecosystem.
  The  scope of the project conducted
during cruises from April to October,
1980,  included the sampling stations
shown in Figures 1  and 2. Quantitative
estimates of phytoplankton abundance at
stations sampled were developed from
replicate counts of permanent slide
preparations. Data  is displayed in the
form of computer-generated plots of
distribution and abundance of major
populations  of interest, statistical sum-
maries of abundance by region and
comparison with 1974 results, and plots
of regional associations based on multi-
variate statistical analyses.
  The final reports document the methods
used  in  sample and data  analysis,
summarize the objective and inferential
conclusions of the study, and provide a
key to the  data and sample archives
resulting from thFs work.

Results
  The  main  results of the study are
summarized in Figures 1  and 2, which
show regional phytoplankton associations
based on multivariate analysis of compo-
sition  and abundance averaged over
season.
  Saginaw Bay (Figure 1) has a graded
series of associations, ranging from those
dominated by eutrophication  tolerant
taxa (region  A) to  increasingly more
oligotrophic  associations at stations

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                        East Tawas
                                         virtually eliminated from wide areas of
                                         the bay.
                                           3. The remaining areas of severely
                                         degraded water quality are in the
                                         southern region of  the bay, which is
                                         directly influenced by the Saginaw River,
                                         at certain stations on the southern shore,
                                         particularly stations 34 and 44.
                                           4. The extent and severity of modification
                                         of phytoplankton associations in the open
                                         waters of Lake  Huron by loadings from
                                         Saginaw Bay has been reduced between
                                         1974 and 1980.
                                           5. There appears to a  continuing long-
                                         term trend toward replacing diatom
                                         dominated associations in  the offshore
                                         waters of Lake Huron with  communities
                                         dominated by microflagellates and other
                                         populations  in  the  nanoplankton  and
                                         picoplankton size range.
                                           6. Regions of phytoplankton similarity
                                         are  variable seasonally, but  there  are
                                         coherent regions of time-averaged similar-
                                         ity which could serve as basis for model
                                         segmentation.
        Bay City

Figure 1.   Regional phytoplankton associations in Saginaw Bay in 1980.
further out the bay (regions 81-63).
Stations  34,  44,  and 54 are extreme
outliers, compared to associations in the
rest of the bay. Assemblages at station 54
are dominated by populations associated
with polluted river conditions. Stations 34
and 44 are apparently affected by local
shoreline loadings and maintain phytoplank-
ton communities characteristic of hypereu-
trophic conditions  similar to those which
dominated wide areas of Saginaw Bay
before  phosphorus loading reductions.

  The  area  sampled in Lake Huron
(Figure 2) has three discrete nearshore
associations (A,B,C) apparently influenced
by differing  types  and  quantities of
shoreline loadings.  Most  perturbed
regions are indicated by subscript 1 and
regions of similar, but less pronounced
effects are  indicated by subscript 2.
Associations  most  characteristic of
oligotrophic environments are found in
regions labeled D. A wide  area extending
northeastward from Saginaw Bay (AD)
supports  associations dominated by
populations usually found in oligotrophic
environments but also  containing other
populations found in Saginaw Bay and
nearshore region A. Although the influence
of nutrient loadings from Saginaw Bay
are detectable in this  region, they are
much less than found in 1974.

Conclusions
  The following conclusions were drawn
on the basis of this study:
  1. Phosphorus loading  reductions
have resulted in a significant decrease in
phytoplankton abundance  in Saginaw
Bay.
  2. There has been a significant change
in the qualitative composition  of the
phytoplankton flora in the bay. There has
been a general shift toward populations
with smaller cell size and certain large,
colonial blue-green algae have been

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                  Statute Miles       fort Huron
        10   0    JO   20   30  140   50
     8400'      8330'      8300'      8230'        8200'      8130
Figure 2.    Regional phytoplankton associations in southern Lake Huron in 1980.

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     E. F. Stoermer. R. G. Kreis, Jr., E. C. Theriot, and T. B. Ladewski are with the Great
       Lakes Research Division, Ann Arbor. Ml 48109.
     Way/and R. Swain is the EPA Project Officer (see below).
     The Project Summary is based on the two reports listed below:
         "Phytoplankton Species Composition, Abundance and Distribution in Southern
         Lake Huron, 1980; Including a Comparative Analysis with  Conditions in 1974
         Prior to Nutrient Loading Reductions," (Order No. PB 83-261 107; Cost: $22.00)
         "Phytoplankton Composition and Distribution in Saginaw Bay," (Order No. PB
         83-261 735; Cost: $19.00)
     The above reports are available only from: (costs subject to change)
             National Technical Information Service
             5285 Port Royal Road
             Springfield, VA 22161
             Telephone: 703-487-4650
     The EPA Project Officer can be contacted at:
             Environmental Research Laboratory
             U.S. Environmental Protection Agency
             6201 Congdon Blvd.
             Duluth. MN 55804
                                                    4US GOVERNMENT PRINTING OFFICE 1983-659-017/7235
United States
Environmental Protection
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