- Library Home /
- Search Collections /
- Open Collections /
- Browse Collections /
- UBC Theses and Dissertations /
- Physical and ecological organization in a large, gravel-bed...
Open Collections
UBC Theses and Dissertations
UBC Theses and Dissertations
Physical and ecological organization in a large, gravel-bed river and response to disturbance Rempel, Laura L.
Abstract
Along the 80-km gravel reach between Hope and Mission, Fraser River has a wandering morphology that includes secondary channels, gravel bars, and islands that together support a diverse and productive ecosystem. The wandering morphology is produced, in part, by annual sediment deposition within the reach. Sediment deposition, however, is perceived as a threat to flood security and gravel mining is proposed as a profitable solution to flood risk. This thesis presents a hierarchical habitat classification for the gravel reach, which provided a spatial framework to, first, examine habitat associations of benthic invertebrates and fish and, second, evaluate the physical and ecological responses to habitat disturbance by gravel mining. At the highest level of the classification, the river is divided into 5 sub-reaches (104 m scale) that vary in morphological expression and sediment gradational tendency. The intermediate level specifies gravel bar units (103 m scale) each consisting of a riffle, gravel bar, and adjacent pool. Nested within gravel bars are physically distinct habitat units, which represent the finest level of the classification (101- 102 m scale). Results demonstrated that the assemblages of invertebrates and fish associated with habitats are moderately distinct and differentiated along a hydraulic gradient corresponding to velocity. However, the congruence between habitat structure and the structure of aquatic communities was weakened by large spatial and temporal variability in the distribution and abundances of many species. This variability was predicted to afford the invertebrate and fish community resilience to physical disturbance. The second component of this study examined the effect of disturbance by gravel mining from an exposed bar in 2000. Physical changes immediately after mining were substantial as the pre existing cobble surface was replaced by loose gravel and sand. Two subsequent freshets transformed the site into a topographically complex area with similar substrate texture as before mining, although sediment replenishment to the site was negligible. Habitat availability at flows <3000 m3 s-1 increased and habitat quality was comparable with reference sites. A third above-average freshet replenished 31% of the removal volume and restored average bar surface elevation to within 9 cm of the pre-scalped surface. Physical changes elicited a significant reduction in invertebrate density immediately after mining, however, the impact lasted less than one freshet cycle. No change in fish density as a result of mining was found, although statistical power to detect an impact was low and fish sampling was carried out at flows <5700 m3 s-1. These results support the expectation that the invertebrate and fish community in the gravel reach has resilience to disturbance from a single gravel removal provided that site recovery by way of sediment transport and replenishment occurs.
Item Metadata
Title |
Physical and ecological organization in a large, gravel-bed river and response to disturbance
|
Creator | |
Publisher |
University of British Columbia
|
Date Issued |
2004
|
Description |
Along the 80-km gravel reach between Hope and Mission, Fraser River has a wandering
morphology that includes secondary channels, gravel bars, and islands that together support a diverse
and productive ecosystem. The wandering morphology is produced, in part, by annual sediment
deposition within the reach. Sediment deposition, however, is perceived as a threat to flood security
and gravel mining is proposed as a profitable solution to flood risk. This thesis presents a hierarchical
habitat classification for the gravel reach, which provided a spatial framework to, first, examine
habitat associations of benthic invertebrates and fish and, second, evaluate the physical and ecological
responses to habitat disturbance by gravel mining.
At the highest level of the classification, the river is divided into 5 sub-reaches (104 m scale)
that vary in morphological expression and sediment gradational tendency. The intermediate level
specifies gravel bar units (103 m scale) each consisting of a riffle, gravel bar, and adjacent pool.
Nested within gravel bars are physically distinct habitat units, which represent the finest level of the
classification (101- 102 m scale). Results demonstrated that the assemblages of invertebrates and fish
associated with habitats are moderately distinct and differentiated along a hydraulic gradient
corresponding to velocity. However, the congruence between habitat structure and the structure of
aquatic communities was weakened by large spatial and temporal variability in the distribution and
abundances of many species. This variability was predicted to afford the invertebrate and fish
community resilience to physical disturbance.
The second component of this study examined the effect of disturbance by gravel mining
from an exposed bar in 2000. Physical changes immediately after mining were substantial as the pre
existing cobble surface was replaced by loose gravel and sand. Two subsequent freshets transformed
the site into a topographically complex area with similar substrate texture as before mining, although
sediment replenishment to the site was negligible. Habitat availability at flows <3000 m3 s-1
increased and habitat quality was comparable with reference sites. A third above-average freshet
replenished 31% of the removal volume and restored average bar surface elevation to within 9 cm of
the pre-scalped surface. Physical changes elicited a significant reduction in invertebrate density
immediately after mining, however, the impact lasted less than one freshet cycle. No change in fish
density as a result of mining was found, although statistical power to detect an impact was low and
fish sampling was carried out at flows <5700 m3 s-1. These results support the expectation that the
invertebrate and fish community in the gravel reach has resilience to disturbance from a single gravel
removal provided that site recovery by way of sediment transport and replenishment occurs.
|
Genre | |
Type | |
Language |
eng
|
Date Available |
2011-10-14
|
Provider |
Vancouver : University of British Columbia Library
|
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.
|
DOI |
10.14288/1.0104992
|
URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
|
Campus | |
Scholarly Level |
Graduate
|
Aggregated Source Repository |
DSpace
|
Item Media
Item Citations and Data
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.