Proceedings - Teaching and Learning Centre - Simon Fraser ...

Fraser River Action Plan 3rd Research Workshop
Introduction
Human Impact on Aquatic and Riparian Ecosystems
in Two Streams of the Thompson River Drainage
R.L. Vadas
CWS/NSERC Research Chair in Wildlife Ecology
Simon Fraser University
In order to determine biological indicators of deforestation, aquatic and riparian fauna and habitat were sampled
in two agriculturally impacted river valleys of the southern interior. The mainstems of the Salmon (SR) and
Nicola (NR) rivers were examined during the fall of 1994 for riparian vertebrates (identified by sight and
sound), riparian invertebrates (caught with a sweep net and aquatic emergence traps), drift and benthic
invertebrates (respectively caught with drift vs. Hess nets), and aquatic mega-invertebrates and fishes (caught
with seine nets and an electroshocker). Whereas vertebrates were indentified to species, invertebrates were
identified to higher taxonomic levels (usually order, suborder or family). Riparian and aquatic habitat were
sampled to determine the relative abundance of habitat types, which included five lower riparian floral
substratum categories, five aquatic-lateral habitat types and seven aquatic-hydraulic categories.
For both streams, middle and lower river sites were examined to make triplet-wise comparisons among sites of
differing upper riparian intactness. The habitat types included forested (FO), semi-forested (SF), shrubby (SH),
and grassy (GR); FO-SF-GR and SF-SH-GR comparisons were made in SR vs. NR, respectively.
Riparian and Aquatic Habitat
Habitat diversity, which was compared in the middle and lower sections of the two rivers (four comparisons),
was often highest at semi-forested sites. Treed sites showed the highest habitat diversity in the lower riparian
zone, via greater abundance of woody vegetation. Aquatic habitat diversity along the lateral gradient was also
hoghest at treed sites of SR, reflecting the greater abundance of edge habitats (backwaters and/or side channels),
whereas NR trends were ambiguous. Semi-forested sites showed the highest hydraulic diversity because pool,
run, and riffle habitats were all abundant, whereas diversity differences among other floral habitat types were
inconsistent. The two most sedimented sites (i.e., the uppermost reaches sampled in SR and NR), were relatively
low in aquatic habitat diversity.
Riparian Vertebrates
Riparian-vertebrate assemblages differed among sites. Higher species diversity and percent abundance of
agricultural species were seen at less-forested sites, whereas logging-sensitive, cavity-nesting birds showed
highest percent abundance at semi-forested sites. Trends for species richness were inconsistent across rivers.
Classification of species into floral habitat-use guilds, as defined in the literature for western North America,
showed that:
• generalists were usually dominant; and,
• treed sites (FO-SF) did not always show greater abundance of treed guilds; and lesser abundance of
unforested guilds.
Guild classification based on the SR-NR data set yielded two ‘treed’ habitat-use guilds (i.e., ‘forested’ (one bird
species) and ‘semi-forested’ (one amphibian and three bird species). There were also five ‘generalist’ bird
species and two ‘unforested’ guilds of birds, including ‘shrubby-grassy’ (one species) and ‘grassy (two species).
Micro- and Macroinvertebrates
Page 247