Headwater streams typically have no fish, owing to steep gradients and impassible barriers;
therefore, scientific research and protection measures have been focused on fish bearing
streams. The Scientific Panel for Sustainable Forest Practices in Clayoquot Sound (CSP)
developed a channel classification system which is pertinent to all streams, fishless and fish
bearing alike, and upon which management prescriptions in Clayoquot Sound, Vancouver
Island, British Columbia are based (CSP, 1995). The CSP classification delineates channels
according to four physical criteria: bed material, gradient, entrenchment, and width. The
current study was undertaken to determine the efficacy with which the CSP classification
system delineates small, steep streams, on the basis of channel geomorphic units within them,
and to examine the benthic macroinvertebrate habitat capability of these geomorphic units.
Falls, bedrock cascades, boulder cascades, rapids, chutes, riffles, glides, and pools were
described according to their bed slope and dominant channel-material type and organization.
In addition, the area of each geomorphic unit was measured. Seventeen streams were grouped
into four CSP channel classes which were compared with respect to the mean relative
proportion of class area in geomorphic units. Stratified random benthic samples were
extracted from geomorphic units in order to investigate and to compare their habitat
capability.
"Alluvial channels" in the study exhibited only weak, very infrequent fluvial transport;
therefore, they were termed semi-alluvial. In general, high gradient geomorphic units (i.e.
bedrock and boulder cascades) were dominant in steep, largely non-alluvial channels. Lower
gradient units (i.e. riffles and rapids) were common in semi-alluvial streams with more mild
slopes. Accordingly, channel classes with opposing bed material and gradient designations
exhibited notable differences with respect to relative proportions of geomorphic units while
width and entrenchment designations exerted little influence on channel organization.
Ultimately, only two of the four CSP classification criteria effectively systematized channels
on the basis of channel geomorphic units within them.
Abundance of benthic macroinvertebrates was greatest in riffles (≈100 individuals per two
minute kick sample), followed by rapids (≈80 individuals/sample), pools (≈70
individuals/sample), boulder cascades (≈60 individuals/sample), chutes (≈50
individuals/sample), and lowest in bedrock cascades (≈25 individuals/sample). In addition,
abundance of invertebrates in channels with ephemeral flow regimes was considerably lower
compared to channels with seasonal or perennial flow regimes. Ordination of
macroinvertebrate taxa showed that community structure of bedrock cascades and chutes
were similar but different from other habitats. Similarly, the benthic macroinvertebrate
community structure of channels with ephemeral flow regimes was very distinct. / Arts, Faculty of / Geography, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/7675 |
| Date | 05 1900 |
| Creators | Halwas, Karen L. |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Format | 9924572 bytes, application/pdf |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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