vvEPA
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
'Research and Development
EPA-600/S3-81-042 Aug. 1981
Project Summary
Response of Phytoplankton to
Acidification in
Experimental Streams
T. W. Weber, II
In order to examine the response of
stream phytoplankton communities to
acidification, three artificial streams
along the Mississippi River were
sampled at biweekly intervals. This
study took place at Monticello,
Minnesota, during late spring—early
summer, 1979. One stream served as
a control with an ambient pH of 8.1,
and two streams were maintained at
pH 6.3 and 5.3 by the addition of
sulfuric acid. The streams provided a
unique replicate system whereby
physical and chemical parameters
could be controlled and continually
monitored in a field situation. The
phytoplankton samples were filtered
onto membrane filters and the con-
stituent phytoplankton species were
enumerated. The diversity of phyto-
plankton was similar throughout all
three pH regimes. However, phyto-
plankton community similarity
decreased over the course of the six
week experimental period. Biomass,
measured by in vivo chlorophyll fluo-
rescence and as the density of the algal
cells, showed a similar pattern. The
pattern of algal community develop-
ment differed across the pH treat-
ments. The phytoplankton at pH 6.3
.and 8.1 attained their maximum
biomass during the first month of
sampling (June). There is a lag in the
population maxima of phytoplankton
at pH 5.3, possibly due to a slower
division rate caused by a less than
ideal pH environment. Species
composition was nearly identical
across the pH range, dominated by
diatoms in each stream. The most
extreme pH value, pH 5.3, seemed to
be a sublethal value for the diatoms
'existing there.
This Project Summary was develop-
ed by EPA's Environmental Research
Laboratory. Duluth, MN. to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
The response of stream phytoplank-
ton communities to acidification was
studied in three experimental streams
at EPA's Monticello Ecological
Research Station near Monticello
Minnesota at two-week intervals from
May 30 to July 11, 1979. Mississippi
River water was pumped into three
streams. The ambient pH of the control
was 8.1; (7.8-8.6) pH 8.1. The other
streams were adjusted to a pH of 6.3
(6.0-6.6) and 5.3 (5-5.7) by the addition
.of sulfuric acid. Phytoplankton samples
were collected and filtered onto mem-
brane filters for a phytoplankton species
enumeration. Biomass measurements
included in vivo chlorophyll fluores-
cence, dry weights and ash free dry
weights. Other measurements taken by
MERS personnel included: temperature,
dissolved oxygen, specific conductance,
hardness, total acidity and alkalinity.
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Phytoplankton density and commu-
nity development differed in each
stream. The density of phytoplankton in
the pH 8.1 and 6.3 streams was highest
during the first month of sampling,
whereas, in the pH 5.3 stream it was
highest in the second month. Phyto-
plankton density was low in all streams
at the end of the sampling period.
Chlorophyll A measurements showed
similar trends. Simpson's Index of
Diversity (the probability that two
individuals picked at random from one
community will belong to different
species) calculated from the phyto-
plankton data showed that all streams
had similar diversity throughout the
sampling period. Morisita's Index of
Community Similarity (a measure of the
probability that two individuals taken
from different communities will belong
to the same taxon) indicated a clear
trend of divergence as each stream
community became more dissimilar
from the others during the study period.
Eight algal taxa constituted as much
as 94% of the algae present and consis-
tently represented the majority of each
stream's phytoplankton community.
However, the pattern of development
differed in the most acidic stream and
the density of algae declined more
rapidly.
The overall species composition was
similar in all streams. Cylotella
meghiniana was the most abundant
species. Diatoms averaged 89.6% (81-
98% range) of the algae enumerated.
Very few of the 48 algal taxa identified
displayed intolerance to any of thethree
pH regimes. However, Euralia lunaris
was not found in the control stream but
became very common in the most acidic
stream whereas, three species of
Navicular. found in the control and pH
6.3 streams, was not found in the pH 5.3
stream. The lowest pH stream appeared
to be a sublethal value for the diatoms
existing there.
Findings of this study are discussed in
relation to the findings of other investi-
gators. Somewhat equivocal results,
from the various cited studies, suggest
that further investigation is needed to
clarify relationships between the phyto-
plankton community and acidification.
Thomas W. Weber, II is with the University of Minnesota, Minneapolis, MN
55455.
Kenneth Hokanson is the EPA Project Officer (see below).
The complete report, entitled "Response of Phytoplankton to Acidification in
Experimental Streams," (Order No. PB 81-216 822; Cost: $8.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Monticello Ecological Research Station
U.S. Environmental Protection Agency
P.O. Box 500
Monticello. MN 55362
U..S. GOVERNMENT PRINTING OFFICE; 1981 — 757-012/7340
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
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