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The effects of fine sediment pulse duration on a stream invertebrate assemblage and growth and mortality of rainbow trout

University of British Columbia

Elevated fine inorganic sediment supply in streams may impair many biological functions, however the contribution of exposure duration to altering these functions has not been previously considered. I evaluated the effects of fine sediment pulse duration on invertebrate assemblages and rainbow trout growth and mortality. I constructed streamside flow-through channels at Moffat Creek in the central interior of British Columbia for this experiment. Fourteen experimental channels, each containing invertebrates and 10 rainbow trout swim-up fry, received fine inorganic sediment treatments of a constant concentration but varied in pulse duration, ranging from 0 to 6 hours per pulse. A pulse was initiated every second day for total of ten pulses over 19 days. Benthic invertebrate abundance and family richness declined (both r²=0.77, P<0.01) as sediment pulse duration increased. Similarly, the family richness of invertebrate drift declined as pulse duration increased (r²=0.20, P=0.04), however, drift abundance increased with increasing pulse duration (r²=0.35, P<0.03). Drift samples were numerically dominated by the family Chironomidae (midges) comprising up to 99% of the drifting insects within the high pulse duration channels. Principal components analysis (PCA) of invertebrate family presence/absence revealed that the primary variation in the drift assemblage (PC1, 27%) was attributed to variation in the presence/absence of Simuliidae; longer pulse duration resulted in the disappearance of Simuliidae (r²0.44 , P<0.01). The primary variation in the benthic assemblage (PC1, 38.8%) was described by the presence/absence of Elmidae, Nemouridae, Baetidae, Leptophlebiidae and Heptageniidae; increasing pulse duration resulted in the virtual disappearance of those families (r²=0.79, P<0.01). Rainbow trout length and mass linearly declined (r²=O.69, P<0.01; r²=0.70, P<0.01 respectively) with increased sediment pulse duration. There was no significant relation (P>0.05) between sediment pulse duration and trout mortality. Analysis of variance revealed that invertebrate, drift, benthos and trout growth were significantly affected by sediment exposure time. Relative to the controls, significant negative changes occurred between the three and five-hour treatments. The hypothesis that trout growth was more affected by direct effects of sediment (e.g. impaired visual feeding ability, physiological stress), than indirectly (through modification of the prey abundance or composition) was tested using path analysis. The results indicate that direct effects were the primary influence of sediment on trout growth although significant alterations of the invertebrate community were observed.

Thesis/Dissertation

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2009-06-27

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http://hdl.handle.net/2429/9778

Forestry

University of British Columbia

UBCV

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