WATER POLLUTION CONTROL RESEARCH SERIES
16030 DQH 11/70
Mayfly Distribution
as a
Water Quality Index
ENVIRONMENTAL PROTECTION AGENCY • WATER QUALITY OFFICE
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WATER POLLUTION CX)NTROL RESEARCH SERIES
The Water Pollution Control Research Reports describe
the results and progress in the control and abatement
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MAYFLY DISTRIBUTION AS A WATER QUALITY INDEX
by
Winona State College
Winona, Minnesota 55987
for the
WATER QUALITY OFFICE
ENVIRONMENTAL PROTECTION AGENCY
Program #16030 DQH
November 15, 1970
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C., 20402 - Price SO cents
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WQO Review Notice
This report has been reviewed by the Water
Quality Office and approved for publication.
Approval does not signify that the contents
necessarily reflect the views and policies
of the Water Quality Office, nor does mention
of trade names or commercial products consti-
tute endorsement or recommendation for use.
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ABSTPACT
Three species of burrowing mayflies ( Hexagenia bilineata, Hexagenia
limbata , and Pentagenia vittigera ) are sufficiently abundant to cause
nuisance problems along portions of the Mississippi River. Mayfly
distribution, as determined by collections made by ship captains and
other cooperators over a 13—year period, has proven to be an excellent
index of general water quality on a river which is so large that it
cannot be monitored effectively or economically by standard methods.
Pollutants hdve severely reduced the numbers of all three species for
30 miles below Minneapolis, Minnesota, and for over 300 miles below
St. Louis, Missouri. P. vittigera is able to emerge only in early
and late sunniier in the St. Louis area when cool water temperatures
lessen toxic effects in the zone of degradation. Impoundment and
enrichment of the Upper Mississippi River has temporarily increased
the carrying capacity of the river for H. bilineata which now domi-
nates areas formerly dominated by Ii. limbata . The total productivity
of the Upper Mississippi is being reduced by pollution, man’s encroach-
ment into the flood plain and by the filling of navigation pools by
sand.
Methods have been developed to rear large numbers of Hexagenia nymphs
in the laboratory. Bioassay tests utilizing artificial, burrow—
containing substrates reveal that H. bilineata nymphs can survive
anaerobic conditions for as long as 11 hours. TLm values for hydrogen
sulfide varied from 0.42 ppm at 48 hr to 0.17 ppm at 96 hr. Of several
heavy metals (Cr, Ni, Zn, Cu) tested, copper was the most toxic to
H. bilineata nymphs. TLm values for copper ranged from 0.54 ppm at
12 hr to 0.27 ppm at 48 hr.
This report was submitted in fulfillment of project WP00987(16O3DQH)—
11/70 under the sponsorship of the Federal Water Pollution Control
Administration.
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CONTENTS
INTRODUCTION..
DESCRIPTION OF STUDY AREA .
METHODS
MAYFLY DISTRIBUTION
Hexagenia bilineata . .
Hexagenia limbata . . . . .
Pentagertia vittigera .
Discussion . . .
TOLERANCE OF HEXAGENIA NYMPHS TO VARIOUS
ENVIRONMENTAL STRESSES
Low Levels of Dissolved Oxygen
Hydrogen Sulfide •
Heavy Metals . .
ACKNC .4LEDCMENTS
LITERATURE CITED . . . . . . . . .
PUBLICATIONS RESULTING FROM STUDY
SELECTED WATER RESOURCES
INPUT TRANSACTION FORM
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Fl GURES
PAGE
Imago Hexa enia limbata mayflies rest upon a tree
branch prior to forming evening mating swarms. 2
2 Hexagenia bilirieata mayflies attracted to automobile
headlights on Mississippi River bridge at inona,
Minnesota, 8 July 1966. 10
3 Vessel used in bioassay experiments with Ilexagenia
nymphs. The burrow—containing substrate is riolded
from polyvinyl acetate plastic.
Hexagenia bilineata numph residing in an artificial
burrow. l
5 Seasonal and geographical distribution of Hexagenia
bilineata on the Mississippi River from Brainerd,
Minnesota, to the Gulf of Mexico as indicated by
collections of imagoes and subimagoes during mass
emergences. Each number indicates the total mass
emergences thus reported at that point during the
interval 1957—1969. 16
6 Seasonal and geographical distribution of Hexagenia
lirnbata on the Mississippi iver from Brainerd,
Minnesota, to the Gulf of Mexico as indicated by
collections of imagoes and subimaGoes during mass
emergences. Each number indicates the total mass
emergences thus reported at that point during the
interval 1957—1969. 18
7 Seasonal and geographical distribution of Hexagenia
bilineata and Hexagenia limbata on the Upper
Mississippi River from Brainerd, Minnesota, to Cairo,
Illinois. Nate that the seasonal distribution of
H. limbata coriplements that of H. bilineata . 19
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FIGURES (cont.)
PAGE
8 Seasonal and geographical distribution of Pentagenia
vittigera on the Mississippi River from Brainerd,
Minnesota, to the Gulf of Mexico as indicated by
collections of imagoes and subimagoes during mass
ernergences. Each number indicates the total mass
emerp,ences thus reported at that point during the
interval 1957—1969. 21
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INTRODUCTION
The general life histories of Hexagenia mayflies are well known (Needham,
Traver, and Hsu, 1935; Hunt, 1953; Fremling, 1960). The burrowing
nymphs construct U—shaped respiratory tubes in the muddy bottoms of
lakes and rivers where they ingest mud, organic detritus, algae and
bacteria. Hexagenia nymphs require from three months to a year to
mature in the Upper Mississippi River, whereupon they rise to the sur-
face, usually at night, cast their nymphal exuviae and emerge as
subimagoes. Subimagoes rest in the shade along the river bank until
the following afternoon when a final molt occurs and the imagoes emerge.
Mating occurs aerially along the shoreline at dusk and the females
return to the river where each alights on the surface and deposits two
egg packets, each of which contains about 4,000 eggs. The eggs sift
downward to the river bottom where most of them hatch in 10—12 days, if
conditions are favorable. Male and female imagoes die within hours
after they have mated.
Hexagenia mayflies tend to emerge en masse , and river residents are ac-
customed to nuisance problems caused by the insects during periods of
maximum emergence. Tree limbs droop under their weight, and drifts of
the insects form under street lights where they decay and create ob-
jectionable odors. Shoppers desert downtown areas as the large, clumsy
insects fly in their faces, cover windows, and blanket sidewalks. In
extreme cases snowplows are called out to reopen highway bridges which
have become impassable. Particles of cast mayfly cuticle cause allergic
reactions in some people. Mayflies become a hazard to navigation when
they are attracted by the powerful arc and mercury-vapor searchlights
used by tow—boats to spot unlighted channel markers. Because mayflies
cause severe nuisance problems, several river cities have tried unsuc-
cessfully to control them.
The name ‘ t Green Bay fly” is often used for the mayfly because people
still recall the hordes of Hexagenia mayflies which formerly arose from
Green Bay of Lake Michigan and literally covered portions of the city
of Green Bay, Wisconsin. Because of pollution, Green Bay flies are now
rare on the lower reaches of the bay near the mouth of the Fox River
(Lee, 1962). Pollution has decimated the Hexagenia rnayfly population
in the western end of Lake Erie (Britt, 1955; Beeton, 1961; Carr and
Hiltunen, 1965). Hexagenia emergences were once common:along the
Illinois River, but pollution has virtually eliminated the insects from
the upper 150 miles of the river (Richardson, 1921; Mills etal., 1966).
Hexagenia mayflies, which were once common along the entiire Upper Mis-
sissippi River, are now rare for 30 miles below Minneapolis, Minnesota,
and for almost 200 miles downstream from St. Louis, Missouri (Fremling,
1964). Hexagenia and Pentagenia mayflies still occur abundantly in
the less polluted areas of the Upper Mississippi River. In Pool 19,
for example, Carlander etal. (1967) estimated the June, 1962, nymphal
Hexagenia population to be 23.6 billion.
Burrowing mayflies are excellent indicators of general water quality
because their life cycles are relatively long. Nymphs are unable to
swim long distances to escape toxic elements, hence their presence or
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FIGURE 1. Imago Hexagenia limbata mayflies rest upon a tree
branch prior to forming evening mating swarms.
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absence in otherwise suitable habitats reflects the quality of the water
which flows over them.
Sampling of the benthos with dredges and other samplers is an extremely
difficult and time consuming task, however. For results to be valid,
large numbers of samples must be taken from many sampling stations.
Collection of adult mayflies, on the other hand, is relatively simple,
less time consuming and much more economical. It is virtually impos-
sible for one investigator to make a significant number of mayfly
collections along 2300 miles river. Therefore, a system has been de-
veloped whereby cooperators assist in the collection of adult insects.
The purposes of this study were to: (1) determine the degree to which
mayfly distribution on the Mississippi River is limited by water
quality; (2) refine laboratory procedures whereby Hexagenia nymphs can
be reared in large quantities; (3) determine the tolerance limits of
Hexagenia nymphs to various limiting factors; (4) learn more about the
biology and ecological importance of burrowing mayflies; (5) to deter-
mine the present distribution patterns of burrowing mayflies along the
Mississippi River so that future habitat changes can be accurately
assessed.
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DESCRIPTION OF STUDY AREA
The Mississippi is the largest river in the United States. From its
source at Lake Itasca, in Northern Minnesota, it winds 2,319 miles to its
mouth in the Gulf of Mexico, 95 miles downstream from New Orleans. The
Mississippi and its tributaries drain about 417. (about 1,244,000 square
miles) of the total area of the United States. By definition, the seg-
ment upstream from the mouth of the Ohio River, at Cairo, Illinois, is
called the Upper Mississippi River (U.S. Army Corps of Engineers, 1958).
The segment from the Gulf of Mexico to Cairo is termed the Lower Missis-
sippi River (U.S. Army Corps of Engineers, 1965). The river is presently
navigated by 9—foot draft vessels as far upstream as Minneapolis.
About 10,000 years ago, the last epicontinental glacier covered most of
Minnesota, extending southward as far as Des Moines, Iowa (Bray, 1962).
The southeastern corner of Minnesota and a portion of western Wisconsin,
however, were left virtually unglaciated. As the glacier melted north-
ward into Canada, it produced a large volume of melt water which could
not flow northward into Hudson Bay because the glacier blocked the Red
River drainage system. Glacial melt waters collected behind the ice dam
to form Glacial Lake Agassiz which covered northwestern Minnesota, extreme
eastern North Dakota, the southern half of Manitoba, southeastern Ontario
and a narrow strip in east central Saskatchewan. Finally, when Lake
Agassiz became overfull, a major portion of its overflow rushed down the
Minnesota River Valley, to enter the Mississippi River at Minneapolis,
Minnesota. This southern outlet stream was named the Glacial River Warren
by Upham in 1884. The flow of the River Warren was augmented by the
Glacial River St. Croix, which drained Glacial Lake Duluth — the ancestor
of Lake Superior. Other smaller glacial rivers, the Mississippi proper,
and the Chippewa added more water to the Glacial Mississippi River which
cut a deep valley through limestone and sandstone strata as far south as
Dubuque, Iowa. Consequently, along the southeastern border of Minnesota,
the Mississippi River flows through a valley which is as much as 650 feet
deep and 3 miles wide. By the time the river reaches Winona, Minnesota,
it has dropped over halfway to sea level. The elevation of the valley
floor at Winona is only 550 feet above sea level, but precipitous bluffs
tower 650 feet above the city.
One hundred and forty—seven years ago, in 1823, the first steamboat
probed its way up the Mississippi River as far as the present site of
St. Paul. The next year, government—owned and operated boats began to
improve the river for navigation by removing snags, boulders and other
obstructions. In 1829, Captain Henry Shreve was commissioned to con-
struct and operate a special twin—hulled snag boat on the upper river.
It was imperative to the growth of the U.S. that the river be improved to
provide a water highway to the sea because the interior of the continent
was relatively inaccessible to overland freight haulers. Early channel
improvements, however modest, enabled the United States to quickly ex—
ploit the interior of the entire North American continent. By the 1870’s
hundreds of shallow-draft steamboats routinely navigated the Upper Mis-
sissippi River.
Loggers used the river, too (Russel, 1928). By means of the Chippewa, the
Black, the Wisconsin and smaller Wisconsin rivers, they quickly exploited
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the pineries of northwest Wisconsin, floating huge rafts of saw logs down
to the Mississippi and then down to the sawmills of Winona, LaCrosse,
Clinton and Rock Island. At one time there were over 80 sawmills on the
upper river and at least 120 more on tributary streams.
In 1878, the U.S. Army Corps of Engineers was authorized by a Congres-
sional Appropriation Act to deepen the navigable channel of the Mississip-.
pi River to four and one—half feet so that larger boats with deeper draft
could operate on the river. This was done by constructing rock closing
dams on side channels so that water which ordinarily went down side chutes
was conducted into the river proper. Obstructive rapids were by—passed
by constructing short lateral canals which contained navigation locks.
Hundreds of rock and brush structures called wing dams were also con-
structed (U.S. Army Corps of Engineers, 1962). The wing dams, often at
intervals of about ¼ mile, extended outward like rock piers from the
shore, at right angles to the main channel of the river. They diverted
the river into a single narrow channel, during low flow, so that the
river scoured its channel deeper. Troublesome sandbars were removed by
a dipper—type dredge. By 1905, the four and one—half foot channel was a
reality between St. Louis and the Washington Avenue Bridge at Minneapolis.
Meanwhile, larger, more powerful riverboats had evolved and they needed a
deeper channel to carry greater pay loads. Additional funds were appro-
priated by Congress in 1907 to deepen the navigable channel to 6 feet.
This was accomplished by building additional wing dams, closing dams, and
by dredging. Usually, on the opposite side of the river from the wing
dams, the shore was fortified with rock so that water which rushed
around the ends of the wing dams did not erode away the opposite shore.
Thus, the extreme channelization begun in 1878 was finally completed in
1912.
The short—lived logging boom which began in 1875 hit its peak in 1892;
and in 1915 the Ottumwa Belle snaked the last remnants of Wisconsin
lumber down the Mississippi River. Six—foot draft steamers also began
to disappear from the upper river because they could not compete with
the railroads.
The Rivers and Harbors Act of 1930 authorized the Corps of Engineers to
modify the obsolete 6—foot channel to provide a minimum depth of 9 feet
and a minimum width of 400 feet (u.s. Army Corps of Engineers, 1962).
This was achieved by the construction of a system of locks and dams,
supplemented by dredging. Most of the resultant 29 locks and dams were
constructed during the 1 9 30’s. A notable exception is Lock and Dam 19
at Keokuk, Iowa, which was constructed as part of a hydroelectric facil-
ity in 1914. The navigation locks are operated and maintained by the
Corps of Engineers, but the U.S. Coast Guard is responsible for the
maintenance of the elaborate system of navigation aids which guide
modern towboats as they navigate the river around the clock from early
spring until early winter.
The huge navigation dams of the tipper Mississippi have transformed the
river into a 8erie8 of impoundments which occupy most of the flood plain
of the river. Consequently, the river is much wider at LaCrosse,
Wisconsin, than it is at New Orleans. Each impoundment coflsist8 of
three distinct ecological areas. The tailwater areas just downstream
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from the dams show the river in relatively unmodified form. The areas
are typified by deep sloughs and wooded islands. The middle portions of
the pools are principally flooded hay meadows. They now provide the
best marsh habitat. The downstream ends of the pools are deeper, however.
They consist mainly of open water and their bottoms are heavily silted.
Marsh vegetation is presently creeping downstream as the pools silt in.
Marsh vegetation in the middle pool areas is being replaced, in turn, by
trees and other terrestrial vegetation.
The old wing dams and closing dams, still partially functional, now lie
beneath the water. The wing dams provide rocky corrugations on the river
floor, so that they, in effect, have increased the total surface area of
the river bottom — thus increasing its carrying capacity for inverte-
brates such as hydropsychid caddisflies and periphyton. Impoundment has
also increased the surface area of the river, thereby increasing the area
of the trophogenic zone.
The seven-county area which contains metropolitan Minneapolis and St. Paul
contains about 1/3 of Minnesota’s population and the population in the
seven—county area is expected to double in the next 30 years. The people
of the seven—county area exert a profound influence on the Mississippi
River.
The river has been severely polluted for many years for about 60 miles
through and downstream from metropolitan Minneapolis and St. Paul (Metro-
politan Drainage Commission of Minneapolis and St. Paul, 1928). In the
metropolitan area about 1,768,000,000 gallons of industrial and municipal
waste water enter the river each day. About 857. of this amount is
cooling water from steam—electric generating plants (Federal Water Pol—
lution Control Administration, 1966). Although they were not constructed
for that purpose, the navigation pools serve as sewage lagoons so that
with each subsequent impoundment and aeration in the tailwaters, the
putrescible portion of the metropolitan pollutant load is decreased.
Downstream cities add more pollutants but their additions are very small
compared to those of Minneapolis and St. Paul. Also, large tributary
rivers such as the St. Croix, Chippewa and Wisconsin add relatively
clean water to the Mississippi thus increasing its ability to assimilate
its pollutant load. Biologically, the Upper Mississippi River is
comparatively clean from Wabasha, Minnesota (mile 760 Upper Mississippi
River), to the mouth of the Illinois River just above St. Louis.
At the mouth of the Illinois, however, the Mississippi receives pol—
lutants from Chicago, other large cities, industries and farms (Mills,
etal., 1966). Prior to 1968, St. Louis added an average of 330,000,000
gallons of raw municipal sewage to the Mississippi every day. This was
supplemented by additional wastes from surrounding municipalities and
from many industries. Just upstream from St. Louis, the Missouri River,
adds an extremely heavy load of silt.
The southernmost darn on the Mississippi River is the newly constructed
Chain of Rocks facility at St. Louis. Downstream 185 miles from St. Louis,
the Ohio River enters the Mississippi at Cairo, Illinois. Here, the
Lower Mississippi begins a 954—mile path through its own immense, flat,
alluvial delta to the Gulf of Mexico. The lower river, at one time,
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constantly changed its course as it meandered about its flood plain.
During the past two hundred years, however, the entire lower river has
been channelized with earthen dikes to prevent flooding of the fertile
delta through which the river flows. Furthermore, the U.S. Army Corps
of Engineers has insured the channelization of most of the lower river
by armoring its banks with rock to prevent the river from changing its
course. The river has also been shortened by cutting off many mean-
ders. Because there are no dams on the Lower Mississippi River, it is
in essence a deep, narrow (200 feet deep, one—half mile wide at New
Orleans), sinuous ditch which conducts most of the effluents of the
United States very rapidly (average flow 611,000 cubic feet per second)
to the Gulf of Mexico.
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METHODS
A system was devised in 1958 whereby various river personnel were
enlisted as cooperators to collect emergent inayflies. From 1958 to
1961 the project was limited to the navigable portion of the Upper
Mississippi River but it was extended in 1961 to include the upper
river to its source. In 1967, the sampling program was extended to
include the entire Lower Mississippi River, its navigable tributaries
and the Gulf Intracoastal Waterway.
Ship captains, lockmasters, harbor operators, resort owners, ferry
operators, and other interested river residents were asked if they
would collect mayf lies whenever they encountered a mass emergence
(Fig. 2). The cooperators were instructed not to collect isolated
individuals but to collect only when mass emergences occurred. Self—
addressed, stamped mailing tubes filled with instructions and alcohol—
filled, plastic, specimen vials were mailed to about 150 cooperators
each spring. Additional collecting materials were distributed to ship
captains by the lockmasters at Lock and Dam Sa and Lock and Dam 19.
The cooperators were asked to record on the specimen vial the name of
the river, mile number, nearest city, time and date.
Shipping strikes, floods, recruitment of new cooperators, and other
uncontrollable variables made it impossible to keep collecting effort
constant from year to year. It was also impossible to maintain con
stant collecting effort over the entire river. There are no navigation
locks on the lower river, consequently collecting was intensified on
the upper river by the lockmasters there. This was particularly true
at Keokuk, Iowa. Lock and Dam 19 is an extraordinarily large facility
and it has more personnel on duty at any one time than any other lock
(with the possible exception of Lock and Dam 27 at St. Louis). Also,
the Mississippi River is not used equally by ship captains throughout
its length. In 1962, for example, about 35 million tons of freight
were transported past Memphis, Tennessee, while less than 10 million
tons were transported as far upstream as Minneapolis. Even the lower
reaches of the Illinois and the Ohio Rivers account for more annual
freight than does the Mississippi River above Reokuk (u.s. Army Corps
of Engineers, 1965).
A concerted effort was made to maintain contact with cooperators.
Publications were sent to them upon request and a newsletter was dis-
tributed frequently. Each fall, the returned specimens were examined
and the resulting data tabulated. Each specimen was examined to
determine its species and sex and whether it was an iniago or subimago.
During the past year all of the data have been transferred to business
machine cards. Programs have been written so that a computer will
print distribution charts for any species, area, year or combination
of years. Figures 5 and 6 are modified computer print outs. In
addition to plotting distributions of the various species, the print
outs are very useful in predicting when an emergence of a particular
species is likely to occur in a given area.
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FIGURE 2. Hexagenia bilineata mayflies attracted to automobile headlights on Mississippi River
bridge at Winona, Minnesota, 8 July 1966.
It
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• “ (t
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The river monitoring program was complemented by laboratory investi-
gations. For this purpose, a 36 ft x 9 ft wet lab was constructed
in the basement of Pasteur Hall at Winona State College. The labora-
tory was outfitted with running well water provided by a sand point
well. Six fiberglas rearing tanks (24 in. wide, 22 in. deep, 72 in.
long) were constructed. Each was fitted with running water, drain,
screen canopy, lights and air bubblers. Rearing procedures were those
described by Fremling (1967).
Bioassay experiments were conducted according to Standard Methods for
the Examination of Water and Wastewater (American Public Health As-
sociation, 1965). A serial diluter, which was constructed according to
the design of Mount and Brungs (1967), metered toxicants during bioassay
experiments.
Attempts were made to study the behavior of Hexagenia nymphs within
their burrows by utilizing thin aquaria filled with mud and water.
Because the nymphs avoided light, however, they usually constructed
their burrows so that little was exposed to the viewer. Hexagenia
nymphs were also used in bioassay experiments to determine their tol-
erance to various toxicants. When test nymphs were aontained in clean,
water—filled vessels, however, they swam constantly as they attempted
to burrow into the bottoms of the vessels. As a consequence of this
activity they became fatigued and their susceptibility to toxicants was
increased. If the bioassay vessels were provided with mud bottoms, the
water in the vessels became turbid and it became difficult to observe
the nymphs. Also, the mud made accurate toxicant monitoring virtually
impossible. Consequently, it became necessary to fabricate inexpensive,
inert, artificial substrates which would be suitable for nymphal behav-
ior studies and for bioassay work (Fremling and Schoening, 1970).
The first substrate was made by imbedding 10 curled pretzels at uniform
intervals around the interior of a 9 in. x 2 in. wooden mold which had
been filled to a depth of 2 in. with epoxy resin and its hardening
catalyst. The resin had been previously mixed with equal parts of dry
sawdust to economize on resin. After the resin block had hardened it
was removed from its mold and allowed to soak until the pretzels became
soft enough to flush out. The edges of the burrows were then trimmed
with a small chisel.
Epoxy resin substrates were quite expensive and it required consider-
able time to construct them. Therefore, a master mold was made of
epoxy resin so that subsequent substrates could be easily manufactured
from a resilient polyvinyl acetate plastic (Fig. 3).
Observation aquaria and bioassay vessels were constructed by building
a tight—fitting glass aquarium around each substrate with glass glue.
When used as bioassay vessels in conjunction with a Mount—Brungs
proportional diluter, the aquaria were fitted with intermittent siphon
drains and the vessels were arranged so that their sides touched, thus
making the burrows dark. Blocks of wood were placed around the perim-
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FIGURE 3. Vessel used in bioassay experiments with Hexagenia nymphs. The burrow—containing
substrate is molded from polyvinyl acetate plastic.
2
‘N.
1.
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eter of the resultant block of vessels so as to darken the outer bur-
rows. At prescribed intervals during the bioassay, the wooden blocks
were removed and the vessels were separated so as to view the nymphs in
their burrows (Fig. 4). Nymphs almost always Leave their burrows
before they die or are evicted by more vigorous nymphs. Thus, it was
possible not only to see which were dead but also those which were
“ecologically dead” (those which were still feebly alive but which had
abandoned their burrows and were thus exposed to predators). Behavior
studies of nymphs within their artificial burrows were best made under
red or yellow light because the nymphs are relatively insensitive to
long wave lengths of the visible spectrum.
When the polyvinyl acetate substrates were newly—constructed they ap-
parently contained excess plasticizer and volatiles which were toxic.
Therefore, they were routinely stored in a well—aerated area until
their smell was gone. They were also washed thoroughly in detergent
water prior to use. Polyvinyl acetate mayfly substrates can now be
obtained from the NASCO Company, Fort Atkinson, Wisconsin, 53538.
Routine water chemistry work was done with a variety of Hach chemical
kits. A colorimeter was used when greater precision was desired.
Toxicant levels of heavy metals were determined with a Beckman model
DB -G spectrophotometer fitted with a Beckman model 1301 atomic absorp-
tion unit and a Beckman laminar flow burner.
Nymphs for most bioassay experiments were raised in the laboratory.
Care was taken to use nymphs which were not in their last instar and
which were fairly uniform in size. Laboratory—reared specimens were
preferred because it was possible to know their species with certainty.
There is no way to positively distinguish medium-sized nymphs of H.
bilineata from those of H. limbata .
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tL 1 A
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FIGURE 4.
Hexagenia bilineata nymph residing in an artificial burrow.
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MAYFLY DISTRIBUTION
Hexagenia bilineata
The biology of H. bilineata has been reviewed by Needham, et al.,
(1935) and by Fremling (1960). The species is very abundant in most of
the navigation pools of the Upper Mississippi River. Most of the
nuisance problems created along the river may be attributable to this
species. The species does well in silted impoundments and it is truly
a “big river” mayfly. Although I once collected the species 8 miles
from the river I have found that the species usually confines its
swarming activities to the river’s edge and its upstream oviposition
flights to the river proper. During a mass emergence, subimagoes may
congregate on either shore if the night is virtually windless. Usually,
however, they are concentrated on one shore or the other by the wind.
Most nuisance problems are caused by imagoes which are attracted to the
lights of boats, bridges and cities during their upstream oviposition
flight (Fremling, 1968). Like the subimagoes, imagoes are usually
wafted by breezes toward one shore or the other. Consequently, a city
on one side of the river may be deluged with mayflies while its sister
city on the opposite side of the river may be free of mayflies. In
general, cities on north or east banks of the river are most prone to
be consistently troubled with mayflies. I have no evidence that this
species seeks out small tributary streams for oviposition.
The silted navigation pools of the Upper Mississippi River provide
excellent habitat for this species. Smaller impoundments upstream
from Minneapolis also provide H. bilineata habitat and the species has
been collected at St. Cloud (mile 927 U.M.R.), Sartell (mile 935 U.M.R.)
and Brainerd (mile 1001 U.M.R.).
H. bilineata is conspicuously rare in the river for 30 miles down-
stream from Minneapolis (Fig. 5). An extremely heavy pollutant load
in that area precludes the existence of the species because the river
bottom is anaerobic for much of the year. Conversations with long-
time river residents have revealed that H. bilineata was formerly
abundant in Lake Pepin (mile 766 — 786 U.M.R.) and that it often caused
nuisance problems in Lake City (mile 773 U.M.R.). Its numbers have
been severely reduced in Lake Pepin in recent years, however. Lake
Pepin evidently serves as a settling basin for pollutants from the
Minneapolis—St. Paul area and also for algae whose proliferation is
caused by upstream fertilization. Chironomid midges have replaced bur-
rowing mayflies throughout most of Lake Pepin. Emergence records
indicate that H. bilineata reaches maximum concentrations in the area
from Dubuque, Iowa (mile 580 U.M.R.), to Keokuk. The species is seldom
reported below St. Louis (Fig. 5). It is unlikely that Vicksburg,
Mississippi, is merely the southern limit of the range of H. bilineata
i the Mississippi River because the species has been collected as far
south as Florida (Berner, 1950). The scarcity of H. bilineata below
St. Louis is due primarily to two factors. The river changes character
at St. Louis (the sight of the last navigation dam) and the swift,
channelized river below St. Louis provides meager habitat. The pol-
lutant load downstream from St. Louis is extreme because of sewage from
15
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1957—1969
HEXAGENIA BILINEATA
MY5 M Cairo Memphis, Vicksburg New Odeans
•g00 100 Oo 700 500 300 100
M es—Upper Mississjpi Rnier Miles -Lower Mississippi River
FIGURE 5. Seasonal and geographical distribution of Hexagenia bilineata
on the Mississippi River from Brainerd, Minnesota, to the Gulf of Mexico
as indicated by collections of imagoes and subimagoes during mass
emergences. Each number indicates the total mass emergences thus
reported at that point during the interval 1957—1969.
16
-------
metropolitan St. Louis itself, but also from the Illinois River. The
Mississippi River at St. Louis becomes an open sewer.
Hexagenia limbata
The biology of H. limbata has been reviewed by Needham, et al. (1935)
and by Hunt (1953). In general, the distribution of H. limbata follows
that of H. bilineata on the Mississippi River (Fig. 6T. H. limbata ,
however, also inhabits tributary rivers, streams and lakes in which
there is sufficient respiratory oxygen the year around. H. limbata is
a versatile mayfly and it is able to occupy a variety of silted habitats
from south-central Canada to central Texas (Hamilton, 1959). On the
Upper Mississippi River, H. limbata occurs farther north than H.
bilineata . Adults of H. limbata have been collected at Little Falls
(mile 965), Brainerd (mile 1000), Aitkin (mile 1055), Grand Rapids
(mile 1180), Bemidji (mile 1304) and Lake Itasca (mile 1365 — the
source of the river).
H. limbata , unlike 11. bilineata , does not confine its mating and ovi-
position activities to the river proper. Whereas the mating swarms of
H. bilineata are usually large and along the river’s edge, H. limbata
swarms may consist of a few individuals, often just above the tree tops
and often several hundred yards from the water’s edge. The oviposition
flights of H. limbata extend far up small tributary streams and even
overland. H. limbata is consistently found farther from the river than
H. bilineata . Mayfly nuisance problems created in the interior areas
of river cities are usually attributable to H. limbata .
H. limbata attains maximum concentrations in the area from Winona,
Minnesota (mile 726 U.M.R.), to Prairie do Chien, Wisconsin (mile 635
U.M.R.). Here a large, early-summer population is apparently due, in
part, to downstream drift of H. limbata nymphs from tributary rivers
such as the Chippewa, Zumbro, Whitewater, Trempealeau, Black and Bad
Axe as well as many smaller streams populated by H. 1imb ta . Prelim-
inary studies conducted at Winona, Minnesota, indicate that large
numbers of Hexagenia nymphs drift down the Mississippi River. Swanson
(1967) reports that mass drifting of Hexagenia nymphs also occurs in
the Missouri River.
It is evident from Figures 6 and 7 that the Keokuk Pool, which produces
many H. limbata in early summer, becomes marginal habitat for H. limbata
in mid-summer. Here, H. bilineata obviously becomes the dominant form
as the summer progresses. It may also be observed that the early,
upstream portion of H. bilineata’s seasonal emergence distribution is
vacant and that the early, upstream portion of H. limbata’s distrib-
ution fits neatly into the space. H. limbata emergences usually occur
prior to those of H. bilineata because H. limbata is able to emerge at
lower water temperatures. Under laboratory conditions, H. limbata has
emerged and flown vigorously at temperatures as low as 14.5 C. H.
17
-------
1957—1969
HEXNENIA LIMB TA
My ea,po s I,aCros e K ktic S Louis Cajro Men)phis Wkst irg New Orlea s
15
25
io ::.
2O
25.
30.
J 5 .
15 • : .
Au 5
• I
25
3
S e 5
15
2
25
9O07O0’5O03O01O0 900 700 500 3O0 100
Mies-1 per P sissippi River MPes—Lcmer Mississippi River
FIGURE 6. Seasonal and geographical distribution of Hexagenia limbata
on the Mississippi River from Brainerd, Minnesota, to the Gulf of I iexico
as indicated by collections of imagoes and subimagoes during mass
emergences. Each number indicates the total mass emergences thus
reported at that point during the interval 1957—1969.
18
-------
1957 1969
hLA/M.±NIA BiLINEATA HEXAGENIA LiMBAii
Minneapolis Dubuque eokuk St. Louis Minneapolis Dubuque Keokuk St. Louts
My 5
10•
15
20
25
30’
Jn
5. , ‘ “
10• ,
15 ‘ . .: .
20
25 “ ‘ “
5
10
15
20•: • • . : •. ,
25 . ‘ , “
• • : “ ‘.
5. , ‘, •, ,, ,
10 •
15 “ ‘ , ‘
20
25
Se 3 °
5.
10
15
20
25
o8 5o6ão5óo4óo3óO2ôOic gOO 30600500400300200
Miles - Upper Mississippi River
FIGURE 7. Seasonal and geographical distribution of Hexagenia bilinêata
and Hexagenia lirnbata on the Upper Mississippi River from Brainerd,
Minnesota, to Cairo, Illinois. Note that the seasonal distribution of
H. limbata complements that of H. bilineata .
19
-------
bilineata , on the other hand, does not emerge under laboratory condi—
tiorks ó from the river until water temperatures reach 18°C (Freinling,
1964; Thomforde and Fremling, 1968). It seems likely that H. limbata
produces a summer generation in the Mississippi River. Late summer
emergences are not as abrupt as those of early-summer, however, because
the latter have not been coordinated by winter.
Like H. bilineata , H. limbata finds the zones of degradation below
Minneapolis and St. Louis unsuitable for habitation. While both H.
bilineata and H. limbata are excellent indicators of good general water
quality, H. limbata is the better indicator of the two on the Upper
Mississippi River.
Pentagenia vittigera
The biology of Pentagenia vittigera is poorly known. The nymphs, which
apparently live in faster water areas than H. bilineata or H. limbata ,
are difficult to collect. Like H. limbata , however, the insect is
versatile and it has been collected from a wide latitudinal area. Ide
(1955) has collected adult P. vittigera along the bank of the Assiniboine
River near its junction with the Red River at Winnipeg, Manitoba. P.
vittigera has also been collected as far south as the Apalachicola River
in Florida (Berner, 1950).
Although Daggy reported in 1941 that the species occurred in the Mis-
sissippi River at Red Wing, Lake City and Minneapolis, Minnesota, the
species is rarely collected in that area now. The seasonal distribution
of P. vittigera is very unusual in the 400—mile segment of river below
St. Louis (Fig. 8). There the insect emerges only during the very early
summer and very late summer, even though it occurs all summer above
St. Louis and from mile 600 L.N.R. almost to New Orleans. The pollutant
load below St. Louis is apparently sufficient to render about 400 miles
of the river uninhabitable during the time when river temperatures are
highest. It seems likely, in that area, that organic enrichment causes
low dissolved oxygen levels during the heat of the summer even though
the river is not impounded. Certainly, summer water temperatures and
low dissolved oxygen levels also combine to make Penta enia nymphs more
vulnerable to the complex of agricultural and industrial pollutants
which enter the river in the St. Louis area. Early summer and late
summer emergences from the 4 00—mile zone below St. Louis are apparently
caused by nymphs which have drifted into the area when low water tem-
peratures and elevated dissolved oxygen levels have made the zone of
degradation less deadly.
Discussion
Because of its impounded state, the Mississippi River provides excellent
habitat for H. bilineata throughout much of the area from Hastings,
20
-------
1957—1969
PENTAGENIA VITTIGERA
My Minnea,pdis LaCrosse Kepkuk St ,Louis Cairo Memphis Vicksb irg New Orle/ans
10•
15
20
25
30
Jn
10
15
20
25
30
JI
10
15
20
25
30
Au
10•
15
20
25
30
Se 5
10-
15-
20-
25-
960 7005O0’3ó0iO0 ‘9óO7OO5OO3OO1ÔO
Miles-Upper Mississippi River Miles - Lower Mississippi River
FIGURE 8. Seasonal and geographical distribution of Pentagenia
vittigera on the Mississippi River from Brainerd, Minnesota, to the
Gulf of Mexico as indicated by collections of imagoes and subimagoes
during mass emergences. Each number indicates the total mass emer—
gences thus reported at that point during the interval 1957—1969.
21
-------
Minnesota, to St. Louis, Missouri. The navigation dams which were
constructed during the 1930’s have undoubtedly increased the carrying
capacity of the Upper Mississippi River for H. bilineata mayflies. It
is likely that this very specialized species now dominates many areas
which were formerly dominated by H. limbata .
Water pollutants are severe limiting factors to mayflies. To a degree,
however, nutrients from metropolitan Minneapolis and St. Paul have
increased the carrying capacity of portions of the Upper Mississippi
River for Hexagenia mayflies. In areas where dissolved oxygen is not
a limiting factor, the enrichment has caused algae to proliferate, thus
causing an increased food supply for burrowing mayflies.
The compact emergence patterns of H. bilineata during late June and of
H. limbata during early June are due to a “stockpiling” of large nymphs
during the winter months. The nymphs are able to grow slowly during
the winter but they are unable to complete last instar development until
early summer temperatures are attained. Thus, early summer emergence
is coordinated by cold winter temperatures. Hexagenia emergences which
occur later in the summer are obviously less well coordinated.
In early summer, the Upper Mississippi River provides good H. limbata
habitat as far south as Keokuk. With increasing summer temperatures,
however, H. limbata becomes less common in the Keokuk area. Increasing
summer temperatures cause the apparent displacement of H. limbata by
H. bilineata in the impoundments near Keokuk.
Water pollution obviously poses a severe threat to the burrowing may—
flies of the Mississippi River. Even if sewage treatment plants
effectively remove most putrescible wastes and fertilizer elements,
other contaminants may eventually erradicate them. Non—biodegradable
insecticides, heavy metals and other toxicants pose serious threats.
Unless sewage treatment keeps pace with population growth and increased
industrialization, burrowing mayflies may be eliminated from the Mis-
sissippi River as they have been in many other areas of the U.S.
(Fremling, 1968).
In many areas of the Upper Mississippi River, roads, dikes and railroads
have dissected the flood plain, thus cutting off the flow of water into
old river channels. Such occluded channels and oxbow lakes stagnate
in the summer and exhibit marked thermal stratification. The hypo-
limriia in such bodies of water usually become deficient in dissolved
oxygen during the summer because of the high biochemical oxygen demand
of bottom sediments. The same lakes often become deficient in oxygen
during the winter when heavy ice and snow cover prevents sufficient
light penetration to produce oxygen by photosynthesis. Such lakes
usually produce no burrowing mayflies. Furthermore, they are death
traps for nymphs which drift into them during spring floods.
22
-------
The most insidious threat to burrowing mayfly populations on the Upper
Mississippi River is sand. Ever since the Wisconsin glacial period the
bed of the river from the mouth of the Chippewa River (mile 763 U.M.R.)
to Keokuk has been slowly rising. Here, sand washed down from pre-
cipitous sandstone—limestone bluffs has entered the river at a rate
faster than the river can remove it. The activities of man (agriculture,
construction, etc.) have greatly accelerated the rate of sand depo-
sition in recent years. The navigation dams, in turn, have provided
places where the sand can accumulate. As a consequence, the pools are
rapidly filling with sand. The U.S. Army Corps of Engineers dredges
constantly to remove sand from the navigable channel of the river, but
the dredged sand continues to accumulate outside the main channel in
the navigation pools. As a consequence, silted river bottoms are
rapidly being replaced by sand bars and islands. Unless corrective
measures are initiated very soon, the Upper Mississippi River will be
transformed into a single, narrow, unproductive channel as is the Lower
Mississippi River.
Burrowing mayflies are good indicators of general water quality because
their life cycles are relatively long. Although nymphs may drift for
considerable distances, they are unable to swim directively for long
distances to escape toxic conditions. It is obvious that even down-
stream drift of nymphs cannot compensate for nymphal deaths in the
most severely polluted segments of the river. Unlike chemical tests
which describe pollutant levels only at the time the tests were taken,
mayfly distribution indicates what water conditions have been like for
a prolonged period. Moreover, while chemical tests only test for
specific pollutants, mayfly distribution indicates the subtle syner-
gistic effects of combinations of many pollutants. This is especially
evident below St. Louis where P. vittigera is only able to emerge in
early and late sunsner. The mayfly distribution data resulting from
this study should also provide valuable baseline data so that future
changes in general water quality can be objectively assessed along the
entire Mississippi River.
23
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TOLERANCE OF HEXAGENIA NYNPHS TO VARIOUS
ENVIRONMENTAL STRESSES
Low Levels of Dissolved Oxygen
Experiments conducted at low levels of dissolved oxygen reveal that
H. bilineata nymphs are very hardy. Bioassay vessels containing
artificial substrates were used as test containers. A siphon with
pinch clamp was fitted so that water could be drawn conveniently
from the vessel at the burrow level for testing. Test vessels were
covered to prevent air from entering. Thus, nymphs were unable to
swim to the water’s surface to obtain oxygen. Observations were
made under yellow light so that nyrnphal activity would not be in-
creased. Control animals in well—oxygenated aquaria were utilized
in all instances.
Four large nymphs were observed as the oxygen level in their test
vessel was gradually lowered, at 25 C, by effervescing the water
with nitrogen. At an initial dissolved concentration of 7 ppm the
nymphs remained quiescent in their burrows with a slow, regular
gill beat (1 beat every 5 sec). The dissolved oxygen level was
gradually decreased to 0.6 ppm over a period of 3 hr and 40 mm.
Swimming movements and a resultant competition for burrows increased
as the oxygen level fell below 1 ppm. After the test period, air
was bubbled into the test vessel and all test nymphs were alive the
following day.
The same 4 nymphs were used in another experiment 2 days later.
The oxygen level, at 24 C, was decreased from 7.2 ppm to zero over
a 4—hr period. As the oxygen level fell below 1 ppm, the nymphs
left their burrows with increasing frequency. At 0.1 ppm the
nymphs lost equilibrium, walked about on the substrate, and swam
occasionally (always toward the surface). Gill movements, which
had increased initially, became erratic at 0.1 ppm and almost
ceased as the D.O. approached 0 ppm. At 0 ppm all 4 nymphs had
abandoned their burrows. Nymphal respiratory movements increased
quickly to 2 beats per sec when nitrogen washing was discontinued
and aeration was begun.
In another experiment, test water was washed with nitrogen for 2 hr
to deplete the dissolved oxygen at 23 C. Ten nymphs of various
sizes were placed in the test vessel at an initial D.O. of 0.3 ppm.
After 41 mm, the nymphs exhibited very little swimming activity,
but their gills moved rapidly (5—10 beats per sec). During the
last 2 hr of the experiment no dissolved oxygen could be detected.
After a total time of 4 hr and 7 mm, aeration was begun and only a
last instar nymph failed to recover quickly. The nymph was thought
to be dead, but it had molted to the subimaginal state by the fol-
lowing morning.
In a subsequent experiment, 6 nymphs were placed in water which con-
tained 1 ppm D.O. at 24°C. The D.O. was then lowered by supple-
mental nitrogen effervescence for 10 hr. After 4 hr at zero D.O.,
25
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the nymphs appeared to be dead. At intervals of about 1½ hr, however,
they swam feebly and then returned to their “dead” position. The
nymphs recovered quickly with oxygenation at the termination of the
10-hr period, having lived through a 9-hr period during which no dis-
solved oxygen could be detected. Further testing revealed that about
one out of 6 nymphs could recover after being treated anaerobically
for 11 hr.
Low D.0. in combination with elevated carbon dioxide levels commonly
occurs in nature. Carbon dioxide was bubbled into a test vessel
(not covered) for 1 hr and 40 mm. During that time the D.0. fell
from 7 ppm to 2.8 ppm while the carbon dioxide level rose from 5 ppm
to 575 ppm. At 50 ppm carbon dioxide, swimming activities increased
markedly. At 100 ppm, equilibrium problems developed. After 1 hr
and 40 mm, carbon dioxide bubbling was discontinued and the vessel
was allowed to stand with no aeration. All the nymphs were dead 12 hr
later.
In another test at 31°C, the initial D.0. was 6.8 ppm and the initial
carbon dioxide concentration was 3 ppm. Carbon dioxide was slowly
bubbled into the water. Seven mm after bubbling began, most nymphs
left their burrows and swam actively. At 17 mm (190 ppm carbon diox-
ide) the nymphs began to lose their equilibrium, ceased swimming, and
lay upside down upon the substrate with gills barely moving. At
40 mm (carbon dioxide 750 ppm, pH 6.1, D.O. 0.8 ppm) all nymphs (10)
appeared dead. Bubbling was continued, however, and two nymphs were
removed at hourly intervals and placed in oxygenated water. Nymphs
recovered after being in the test situation for as lov g as 3½ r.
From the previous experiments it is evident that H. bilineata nymphs
can tolerate extremely low dissolved oxygen levels and extraordinarily
high carbon dioxide levels for several hours. The nymph’s first
reaction to these conditions is to abandon its burrow and to swim to
the surface. In rearing chambers which were caused to go anaerobic
because of the addition of substances which had a high biochemical
oxygen demand, the nymphs came to the surface and crawled partially
out of the water so as to expose their gills to the atmosphere. The
same phenomenon has been observed in late winter on the Mississippi
River where oxygen levels in sloughs have dropped. There the nymphs
congregate in muskrat runways and in holes cut by fishermen. After
prolonged low oxygen levels, the nymphs become torpid and lie on the
bottom seemingly dead, but are able to recover in oxygenated water.
In nature, nymphs undoubtedly swim actively or drift long distances
with the current to escape low oxygen conditions. It is obvious that
nymphs could drift passively for over 20 miles through a zone of
degradation if the current speed approached 2 mph.
26
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Hydrogen Sulfide
The effects of hydrogen sulfide have been determined on certain fish
and aquatic organisms (McKee and Wolf, 1963; Bonn and Follis, 1967;
Jones, 1948; Van Horn, Anderson, and Katz, 1949). The studies
present conflicting results in several instances, however. This is
probably because the early studies did not account for varying pH.
Bonn and Follis (1967) state that the toxicity of hydrogen sulfide
to channel catfish varies with changes in pH of the solution. It is
known that hydrogen sulfide dissociates primarily according to pH,
with temperature and other factors playing a minor role (McKee and
Wolf, 1963). In general, the lower the pH, the greater the degree of
dissociation.
In the present study, 10 laboratory—reared H. bilineata nymphs
(20—25 mm in length) were placed in each of five bioassay vessels
(previously described). The volumes of the mixing chambers of the
serial diluter were adjusted by placing marbles in the chambers to
give final dilutions of 20 ppm, 10 ppm, 5 ppm, and 2.5 ppm of total
hydrogen sulfide. The fifth bioassay vessel received no toxicant,
thus serving as a control. A stock solution of hydrogen sulfide was
prepared by saturating distilled water with sodium sulfide. The
stock solution of hydrogen sulfide was placed in a Mariotte bottle
and the serial diluter allowed a small quantity of this solution to
enter each mixing chamber at the start of each cycle.
The pH of the water in the test vessels was determined to be 7.9.
The dissolved total sulfide content was tested with a Hach colorimeter.
The un—ionized hydrogen sulfide was calculated from the dissolved
total hydrogen sulfide and the pH of the sample (American Public
Health Association etal., 1965). The bioassay vessels were aerated
by the discharge from the serial diluter, and the D.O. varigd from
5.5 ppm to 6.2 ppm. The test was conducted for 96 hr at 22 C.
About 24 hr after the test began, the nymphs showed some effects of
the hydrogen sulfide. In the bioassay vessels with the greater
concentrations, nymphs deserted their burrows and began to move their
gills very rapidly. It was several hours after they left their bur-
rows that the nymphs actually died. The nymphs were considered to be
dead when all visible gill movements had ceased and they failed to
respond to mechanical stimuli.
TL values varied from .42 ppm at 48 hours; to .21 ppm at 72 hours;
ppm at 96 hours. All TL s are given in ppm of un—ionized
hydrogen sulfide rather than to’ al dissolved hydrogen sulfide.
From the previous experiments with dissolved oxygen, carbon dioxide
and hydrogen sulfide it is apparent that Hexagenia nymphs abandon
their burrows long before they succumb to toxic concentrations of the
three gases. In nature, depressed D.O., and elevated carbon dioxide
and hydrogen sulfide levels occur commonly in areas where high B.O.D.
materials accumulate at the mud—water interface. These conditions
force nymphs from their burrows, thus causing their “ecological
death” in many instances. Those nymphs which are not killed by
27
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predators must either swim to better habitat or enter the current so
that they can drift downstream. In areas where no current exists,
nymphs swim upward to escape toxic conditions at the mud—water inter-
face. Although the water at higher levels may not be toxic, the
nymphs are not adapted for life there. Their specific gravity is
such that they begin to sink as soon as they stop swimming. Thus,
when exhausted from swimming, they sink to their deaths on the surface
of the mud. The latter situation has been observed several times in
laboratory rearing tanks.
Heavy Metals
The acute toxicities of several heavy metals to Hexagenia mayfly nymphs
were determined by flowing water bioassay procedures. As indicated
previously, a Mount Brungs diluter was used to meter out the various
toxicants. Ten nymphs were placed in each of five bioassay vessels
which contained artificial substrates. Four of the vessels contained
various dilutions of toxicant. The fifth vessel served as a control.
Whenever possible, laboratory—reared nymphs were used so that their
species was known with certainty. Occasionally, however, it was
necessary to dredge nymphs from the river. Laboratory—reared nymphs
were preferred because they were priorly acclimated to laboratory
conditions. Nymphs of relatively uniform size were used. Nymphal
length was determined by measuring from the anterior tip of the
pronotum to the posterior end of the abdomen.
The well water used in the bioassay tests was monitored regularly.
Total hardness during a one—year test period varied from 357 to 448
ppm, calcium hardness varied from 187 to 238 ppm, and total alkalin-
ity varied from 289 to 391 ppm. Nitrates, nitrites and phosphates were
not present in detectable concentrations. With minor exceptions,
temperature varied from 24 to 28 C and pH varied from 7.0 to 7.3.
Oxygen concentrations were relatively constant in the bioassay vessels,
varying from 35 to 507. of saturation. Toxicant concentrations for all
metals (with the exception of mercury) were determined by standard
flame emission analyses with an atomic absorption spectrophotometer.
Numerous runs were made with each toxicant in an effort to obtain U
values for 12, 24, 48, 72 and 96 hr. Results of these tests are m
suimnarized in Table I.
Zinc
The toxicity of zinc to various species of fish has been suninarized
by Skidmore (1964), Doudoroff and Katz (1953), McKee and Wolf (1963),
Pickering (1968), and Brungs (l969 . Mount (1966), in his work with
the acute toxicity of zinc to fathead minnows ( Pimephales promelas) ,
reports that toxicity increased at high pH leveis and that precipi-
tated zinc may have accounted, in part, for the increased toxicity.
28
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In my tests, zinc precipitated out (presumably as zinc carbonate) at
concentrations in excess of 12.5 ppm. The zinc precipitate had no
apparent detrimental effect on test nymphs even though it accumulated
visibly in their burrows. It was noted, however, that nymphs seemed
to moult with unusual frequency during the tests. At the pH and
hardness levels utilized in these experiments, zinc at 12.5 ppm ex-
hibited no apparent toxicity, even during a 96—hr period. Galvanized
stock watering tanks have been used with excellent results for 10
years for rearing Hexagenia nymphs in my laboratory. Thousands of
insects have been reared through complete life cycles in galvanized
containers.
Copper
In flow—through bioassay experiments to determine the toxicity of
copper to adult fathead minnows, Mount (1968) obtained a 96—hr TLrn
value of 0.47 ppm in water which ranged in pH from 7.9 to 8.5
(mean hardness 198 ppm as CaCO 3 ). In soft water (ph 7.7 - 8.1,
total CaCO 3 hardness 35 — 50 ppm), Arthur and Leonard (1970) deter-
mined average 96—hr TLm values for copper to be 1.7 ppm for
Campelorna decisurn snails, 0.039 ppm for Physa integra snails and
0.02 ppm for Gaminarus pseudolimnaeus amphipods. Warnick and Bell
(1969) tested the effects of copper on the mayfly Ephemerella
subvaria and the stonefly Acroneuria lycorias . In water which had a
pH of 7.25 and total hardness of 44.0 ppm, they obtained a 48-hr
TLrn of 0.32 ppm for E. subvaria and a 96-hr Urn of 8.3 ppm for A.
lycorias . In my experiments, copper was extremely toxic to H.
bilineata nymphs. TLm values were 0.54 ppm for 12 hr, 0.34 ppm for
24 hr and 0.22. ppm for 48 hr.
Nickel
Nickel, even at concentrations of 27.2 ppm, caused no mortality among
H. bilineata nymphs for periods as long as 96 hr. Warnick and Bell
r1969) in experiments with softer water (alkalinity, 40 ppm; hard-
ness, 44 ppm), report 96-hr TLm values of 4 for the mayfly Ephernerella
subvaria and 33.5 for the stonefly Acroneuria lycorias.
Chromium
Chromium was relatively toxic to Ilexagenia nymphs. TLm values ranged
from 12.8 ppm at 48 hr to 8.6 at 96 hr. Warnick and Bell (1969)
report a 96-hr Urn value of 2 for E. subvaria.
Mercury
During the summer of 1970, many bioassays were conducted with mercury.
I was unable, however, to determine precise toxicant levels because
29
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Table I
Results of bioassays to
determine TLm values for
various heavy metals.
TON SOURCE TLm (ppm) TEMP SPECIES SIZE
12 hr 24 hr 48 hr 72 hr 96 hr
Cr K 2 Cr 2 O 7 12.8 17.1 8.6 26—27C Hexagenia 8—19
Ni NiSO 4 greater 26—27C H. bilineata 20—28 mm
than
27.2
0
Zn Zn 50 4 greater 24—25C H. bilineata 15—25 mm
than
12.5
Cu CuSO 4 0.54 0.34 0.22 24-25C H. bilineata 15-25 mm
Cd CdSO 4 Tests run, but final toxicant levels not determined
Hg H Cl 3 Tests run, but final toxicarit levels not determined
-------
of the lack of sensitivity of our atomic absorption unit for this
element. Toxicant concentrations were estimated emperically and
water samples were taken from the test vessels at regular intervals.
The samples were preserved in sealed glass bottles for analysis
when improved atomic absorption procedures could be instituted. At
present, we are constructing the necessary apparatus to do the
analyses according to methods described by Fishman (1970). It was
possible, by the method previously described, to make determina-
tions of the 12, 24, 48 and 96 TLm for mercury. Although precise
determinations cannot be yet reported, mercury is apparently very
toxic with a 24—hr TLm level of less than 1 ppm. In their work with
the mayfly Ephemerella subvaria , Warnick and Bell (1969) report
96—hr TLm values of 2 ppm for mercury.
31
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ACKNOWLEDGMENTS
I wish to thank the many ship captains, lockmasters, marina operators
and river residents who have collected mayflies for the past 13 years.
This study would not have been possible without their assistance.
My students were a constant source of encouragement. Deserving of
special thanks in this regard are Roger Flattum, Henry Nilsen, Donald
Hemming, Larry Thomforde, Gary Schoening, Elaine Thrune, Angie Boetcher,
Pearl Yamasaki, Mark Pluim, Jerry Nagahaski, Robert Keller, John McLeod
and Peter Pelofske. My son, Mark, and my wife, Arlayrie, helped in
many ways. I especially appreciate the encouragement provided by
Dr. Robert DuFresne, President of Winona State College; Dr. Nels Minne’,
Past President of Winona State College; Dr. Dan Willson, Dean of the
College of Science, Literature and Arts; and Dr. Donald Warner,
Academic Dean.
33
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38
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PUBLICATIONS RESULTING FROM STUDY
Fremling, Calvin R. 1967. Methods for mass—rearing I-iexagenia
(Ephemeroptera: Ephemeridae). Trans. Amer. Fish. Soc. 96(4):
407—410.
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Hexagenia mayfly nymphs. Proc. Internat. Congr. Ephemeroptera.
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1 Accessjon Number
2 Subject
Field & Group
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
5 Organization
Winona State College, Winona, Minnesota
6 Title
Mayfly Distribution as a Water Quality Index
10 Author(s)
Calvin R. Fremling
11 Date
December 16, 1970
12 Pages
39
15 Contract Number
16 Project Number
WP00987(16O3DQH)]J/ 70
21 Note —
22 Citation
Final Report, Federal Water Pollution Control Administration
23 Descriptors (Starred First)
MAYFLY DISTRIBUTION HEXAGENIA
WATER QUALITY PENTAGENIA
EPHEMEROPTERA MISSISSIPPI RIVER
25 Identifiers (Starred First)
As above.
27 Abstract
Three species of burrowing mayflies ( Hexagenia bilineata, Hexagenia limbata , and
Pentagenia vittigera ) are sufficiently abundant to cause nuisance problems along
portions of the Mississippi River. Mayfly distribution, as determined by collections
made by ship captains and other cooperators over a 13—year period, has proven to be
an excellent index of general water quality on a river which is so large that it can-
not be monitored effectively or economically by standard methods. Pollutants have
severely reduced the numbers of all three species for 30 miles below Minneapolis,
Minnesota, and for over 300 miles below St. Louis, Missouri. P. vittigera is able to
emerge only in early and late summer in the St. Louis area when cool water temper-
atures lessen toxic effects in the zone of degradation. Impoundment and enrichment
of the Upper Mississippi River has temporarily increased the carrying capacity of
the river for II. bilineata which now dominates areas formerly dominated by H. limbata .
The total productivity of the Upper Mississippi is being reduced by pollution, man’s
encroachment into the flood plain and by the filling of navigation pools by sand.
Methods have been developed to rear large numbers of Hexagenia nymphs in the
laboratory. Bioassay tests utilizing artificial, burrow—containing substrates
reveal that II. bilineata nymphs can survive anaerobic conditions for as long as 11
hours. TLrn values for hydrogen sulfide varied from 0.42 ppm at 48 hr to 0.17 ppm
at 96 hr. Of several heavy metals (Cr, Ni, Zn, Cu) tested, copper was the most toxic
to H. bilineata nymphs. TLm values for copper ranged from 0.54 ppm at 12 hr to
0.22 ppm at 48 hr.
Abstractor: C. R. Fremling
Institution
Winona State College
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