8141A

• UCREFRP Catalog Number: 8141A
• Author: Wydoski, R. S. and W. T. Helm.
• Title: Effects of Alterations to Low Gradient Reaches of Utah Streams.
• USFW Year: 1980.
• USFW - Doc Type: \
• Copyright Material: NO

interval by following equation 9 using the nearest population estimates on
either side of the time period. Although this technique produces no new
information on population size, it provides a more reliable estimate of
production over long periods of time by providing more accurate growth rates.

Macroinvertebrates

Tw~ types of sampling devices were employed: a Hess sampler (total area
1380 cm ) with a 0.25 mm mesh net, and basket-type samplers. The basket
samplers have been proven to be effective in small streams in this region
(Israelson et al. 1975). They are easy to use and less subject to sampling
technicians variability than most methods. Their disadvantages are the time
necessary for colonization by macroinvertebrates, their vulnerability to loss
by vandalism, and loss due to substrate movement.

The bas~ets (total area 225 cm2) were 15 cm cubes constructed of 1.2 mm
hardware cloth with 0.25 mm mesh nitex cloth in the bottom. This design allows
lateral movement of invertebrates, but prevents vertical movement out of the
sampler, especially during retrieval. The baskets were installed by digging a
narrow trench perpendicular to stream flow, filling the,baskets with some of the
removed substrate, placing the baskets in the trench and replacing substrate
around them. They remained in the stream for a minimum of two months prior to
sampling. This period of time was found to be adequate for the macroinvertebrate
community to become re-established (Brooks 1971). Basket samples were taken by
grasping the edges of the basket, rapidly lifting it straight up out of the
water, and depositing it in a 12 1 plastic tub.

The Hess sampler (total area 1380 cm2) with a 0.250 mm mesh net was used
for comparison with the basket samplers and to obtain sam~les when basket
samplers were no longer in place. The Hess samples'were taken in the vicinity
of baskets (~ 10 m of stream). The substrate was loosened to a depth of
10-15 cm if the material was not compacted and washed thoroughly. The sample
was then transferred to a 12 1 plastic wash tub.

The original sampling schedule was to collect two samples monthly with each
sampler at each site. However, the loss of basket samplers reduced the number
of samples that were collected by this method (Appendix E ; Table 3 ).

All samples were processed by the following method. Large pieces of sub-
strate were carefully washed off and removed from the tub. The sample was then
sugar floated three times to separate the invertebrates and organic matter from
the gravel and sand (Anderson 1959). The gravel and sand were discarded and the
sample was washed with fresh water through a 0.25 mm diameter mesh sieve and
placed in a clean tub. The sample was then washed through a US #5 sieve (4.0 mm
diameter openings) into another tub and the fraction retained was placed in a
separate bottle. This process was repeated for the entire sieve series (US #s
5, 7, 10, 14~ 18, 25, 35, 45, 60 with corresponding mesh openings of 4.0, 2.80,
2.00, 1.50, 1.00, 0.710,0.500,0.355,0.250 mm). This series corresponded to
alternate sieves in the test sieve aperture series recommended by the Inter-
national Standards Organization, Geneva, Switzerland. (The log of the opening
in mm is highly correlated with sieve size (each sieve = 1 x axis unit and
can be described by the regression y = -.150104311x + .749940750; r = -.999988.)
The samples were preserved in 10% formalin and returned to the laboratory.
\~hile invertebrates preserved in formalin lose weight (Howmiller 1972; Winberg

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