fic; ice covered without traffic; and ice free with
density differences across the river. They did note
traffic. However, they were unable to obtain ad-
such a trend at one site, Frechette Point, but this
ditional data for ice-covered conditions with vessel
was only during the winter field period when wind
traffic. Their major conclusions include:
waves would not be active due to the ice cover.
Macroinvertebrate drift was less for ice-cov-
Consistently greater drift densities at Frechette
ered conditions without vessel traffic than
Point than at the other two sites were attributed
for open-water conditions with traffic.
to higher ambient water velocities there.
The average density and biomass of macro-
When comparing their data to the earlier studies
invertebrate drift was higher in the naviga-
of Poe and Edsall (1982) at Frechette Point, they
tion channel than in nearby littoral waters.
found that their winter, under-ice drift density
was 2000% greater (989 vs. 47/1000 m3) than in
The amount of macrophyte drift for ice-
covered conditions without vessel traffic was
that earlier study. Similarly the 1985 summer mea-
less than that found during the 1979 study
surements showed a drift density 2600% greater
(1659 vs. 64/1000 m3). While they cited annual
(Poe et al. 1980) for ice-covered conditions
with vessel traffic.
biological variations and slight variations in sea-
Zooplankton biomass was higher in the navi-
sonal sampling times as a partial cause, they felt
gation channel than in littoral waters.
that the disagreement was primarily due to dif-
Detrital biomass was higher in the channel
ferences in sampler mesh sizes. There was also
than adjacent littoral waters for three out of
disagreement between the two studies as to the
four locations sampled.
variation of drift density with depth. While Poe
They concluded that drift rates for all com-
and Edsall found that drift density decreased from
ponents were considerably higher when there
the surface to the bottom, Jude et al. found drift
was navigation in ice than when there was ice
densities to increase with depth. The cause of this
and no navigation or when there was naviga-
disparity was considered unexplainable, but sea-
tion in open water. They also concluded that navi-
sonal biological variations and slight differences
gation in ice can cause considerable amounts
in sampling dates were again cited as possible
of detritus, macrophytes, zooplankton and macro-
contributors.
invertebrates to be transported out of the sys-
Jude et al. (1986) considered it highly prob-
tem. While they noted that the significance of
able that vessel passage could result in increased
benthic drift, and based on visual observations
these losses could not be addressed with avail-
they speculated that upbound vessels would have
able data, they felt that it was important that
the greatest impact on drift density. In reviewing
the losses would occur at a time when produc-
their data, however, they were unable to demon-
tion reaches an annual minimum.
strate detectable increases in the density of drift-
Jude et al. (1986) examined benthic drift at three
ing benthos due to vessel traffic. Noting the windy
sites on the lower St. Marys River during 1985,
conditions prevalent during data collection, they
including Frechette Point, lower Lake Nicolet and
concluded that ship passage had not significantly
Point Aux Frenes. In addition to collecting con-
altered the already disturbed system.
secutive samples over approximate 12-hour time
While considering the distance that disrupted
increments during one winter and one summer
benthos might be expected to travel in the St. Marys
field period, they also collected a series of five-
River before resettlement, Jude et al. speculated
minute samples during the passage of vessels dur-
that a great proportion resettle within a short dis-
ing the summer. During the study a total of 71
tance, with only a small fraction consumed or
taxa were identified. Drift densities during both
destroyed by drifting activity. Since the period
winter and summer were found to be significantly
of ship disturbance is very short-lived in com-
greater (9002200%) at night than during the day
parison with wind events, which could last for
for all comparisons except at Frechette Point in
hours or days, they concluded that ship-induced
summer. At all sites the number of taxa collected
drift would resettle more quickly than wind-
was greatest at night regardless of the season.
induced drift. On that basis they felt that drift
While the study of benthic density and diver-
induced by windy weather has a greater overall,
sity by Liston and McNabb (1986) found lesser
river-wide effect on drift than individual, though
benthic densities along the eastern shore, which
frequent, ice-free ship passages. They did not
they attributed to greater scouring of the bed by
collect data for ship passages in ice.
waves driven by prevailing winds from the west,
Based on their review of the field data of Poe
Jude et al. found a general lack of benthic drift
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