8092

• UCREFRP Catalog Number: 8092
• Author: U.S. Department of the Interior.
• Title: Proceedings of the Symposium on Restoration Planning for the Rivers of the Mississippi River Ecosystem.
• USFW Year: 1993.
• USFW - Doc Type: Washington, D.C.
• Copyright Material: NO

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conditions available for algal colonization and
growth. Consequently, algal communities are good
indicators of stream health and can serve as im-
portant biological monitors. The variation in com-
munity composition that exists among subhabitats
within streams and among individual streams
(Douglas 1958; Krecji and Lowe 1986; Pringle
1987) can be uSed as a tool to understand problems
that exist within the watershed. Variation in com-
munity composition can be attributed to differ-
ences in the nutrient availability of surface waters
(Eminson and Moss 1980), size and biological ac-
tivity of substrata (Miller et al. 1987; Carlton and
Wetzel 1988), and substrate type (Stevenson and
Hashim 1989).
In situ algal bioassays were conducted at one
mainstem and four tributary sites in 1990. Bioas-
says were done with nutrient-diffusing artificial
substrata similar to those of Fairchild and Lowe
(1984). Sites were chosen that were similar in
water velocity and shading. Four potentially lim-
iting nutrient treatments and a control were at-
tached to a 1.5-m-long, 2- x 6-cm board (Bushong
and Bachmann 1989). Six boards were placed at
each site, 10-15mapart.After7 days, three boards
at each site were randomly chosen and analyzed
for periphyton. The three remaining boards were
removed and periphyton sampled after 14 days.
Chlorophyll a, organic weight, inorganic weight,
and fine sediment accumulation were measured in
the laboratory. Turbidity, water velocity, and
maximum-minimum temperatures were moni-
tored at each site.
The proportion of the substrate composed of
particles less than 2.4 mm in diameter ranged
between 47 and 1000Al in mainstem sites and be-
tween 33 and 75% in tributary sites. Iwamoto et al.
(1978) and Rivier and Sequier (1985) stated that
the presence and addition of fine sediments
(<2.4 mm) to lotic systems can have strong effects
on biotic communities and functional parameters.
Existing algal communities were identified on
hard substrates at six sites. Thirty-nine taxa of
diatoms, green algae, and bluegreen algae were
found. Diatoms were dominant at all sites (66-
92%), represented by 16 taxa. The most abundant
diatoms were Cyclotella spp. and various pen-
nates. Twenty-three algal taxa were identified.
The most abundant were the green algae Ankis-
trodesmus spp., and Scenodesmus spp.
The greatest differences among the sites seemed
to be partly attributable to available substrate con-
ditions. Sites with a diversity of substrates ranging

CHRISTOPHER M. KAVANAUGH 13

from cobble and gravel to detritus and woody debris
had a greater diversity of algal taxa.
The relative influence of nutrients on algal pro-
duction in this study was low. The phosphorus and
nitrogen-phosphorus treatments had statistically
significant stimulatory effects on chlorophyll a
and biomass accrual; but the overall effect was
small. Water chemistry data indicate that the
streams all have relatively high concentrations of
nitrates and phosphorus, but N:P ratios varied
considerably.
The variation in overall algal biomass and pro-
duction among sites may be attributed to differ-
ences in quantity of available colonists, and conse-
quent colonization and deposition of algal
material. Other studies of midwestern streams
have implicated water temperature and light as
being more important than nutrients in controlling
algal production (Bushong and Bachmann 1989;
Munn et al. 1989). Water temperatures did not
vary more than 30 C during this study and did not
seem to be a controlling factor. However, because
of the high levels of turbidity, light may have been
limiting. Turbidity values recorded were as high or
higher than values observed by Munn et al. (1989)
to impair algal production (>10 NTU). In addition
to the reduction of light, suspended sediments
accumulated directly on the artificial substrates.
There were also at least two storm events that
carried elevated sediment loads that could have
scoured algae from the test substrates.
Sampling and analysis of algal communities is
continuing at 20 sites on minor watersheds. Devel-
opment of diverse periphyton communities
throughout the Minnesota River basin seems to be
limited by lack of stable substrates, high turbidity,
high sediment loads, and predominance of fine
sediments.

Macroinvertebrates

Benthic macroinvertebrates are important indi-
cators of water quality (Hynes 1970). Aquatic
macroinvertebrates are found in nearly all stream
habitats and display a wide variety of functional
feeding characteristics (Merritt and Cummins
1984). Environmental requirements and pollution
tolerance information are available for most taxa.
These factors make aquatic macroinvertebrate in-
dices useful in assessing water quality.
Macroinvertebrate data from the Minnesota
River have been collected by several investigators
over the years (Kirsch et al. 1985). Previous inves-
tigations focused on only a small portion of the