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Hydrogeomorphic controls on spatial pattern of fish habitat in a mountain stream

University of British Columbia

Spatial heterogeneity and arrangement of physical habitat strongly influence stream-dwelling organisms. A primary objective of this dissertation was to examine how hydrogeomorphic controls – channel morphology, bed sediment, and flow hydraulics – shape spatial patterns of habitat for small-bodied trout. Two complementary habitat types, spawning and foraging habitat, were investigated to gain more comprehensive understanding of these linkages. A secondary objective of the dissertation was to evaluate the effects of sample size on errors in estimates of hydraulic parameters critical for understanding channel dynamics and quantifying fish habitat. This research was conducted in four reaches of a small mountain stream with different channel morphologies and sediment textures. High resolution field surveys and a hydrodynamic model were used to map channel morphology, sediment, and flow properties. Habitat models, which included a bioenergetic foraging model, were then applied to evaluate fish habitat availability, quality, and disturbance at within and between-reach scales. Results indicated existence of two distinct spawning habitat domains. In coarser reaches with simple morphologies potential spawning substrate occurred only in small, hydraulically sheltered areas, which were also at high risk of disturbance due to excess fine sediment accumulation. In finer, pool-riffle reaches potential spawning substrate covered large proportion of the bed and was largely unaffected by fine sediment disturbance. Bed scour generally did not seem to be an important disturbance agent. During low flow, the most energetically profitable foraging habitat was located in deep, slow-flowing pools and zones of strong lateral gradients of velocity. Cross-channel patterns of net energy intake appeared to vary with fish body size. During high flow, however, energetically profitable habitat occurred mainly near the banks. The mean net energy intake and the proportion of channel area where fish energy budget was positive were somewhat higher in the reaches with better developed pool-riffle morphology, but the former trend partially reversed during high flow. Error analysis indicated that sample sizes commonly used in river science to represent hydraulic variables may generate large sampling errors. Errors of this magnitude in the estimated bed roughness parameter caused substantial differences in the flow field predicted by a hydrodynamic model.

Text

2015-04-30

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/50683

Geography

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/