The Effect of Riparian Alteration on Brook Trout Populations, Stream Morphology, and Invertebrate Communities

Abstract

Riparian vegetation influences stream morphology, habitat and biological communities providing a source of connectivity between aquatic and terrestrial ecosystems. The objective of this study was to determine how riparian vegetation, including the removal of Tag Alder in the riparian corridor and addition of brush bundles, effects stream morphology, Brook Trout Salvelinus fontinalis habitat and feeding, and invertebrate communities. We sampled four sites, May through September 2017, with different types of riparian vegetation at Green Meadow Creek Lincoln County, WI. Three of these sites were references that represent the different types of vegetation found in the area, second growth forest, shrub or Tag Alder Alnus incana, and sedge meadow. The fourth site was experimental and consisted of a Tag Alder riparian area. Here, Tag Alder was removed and used as brush bundles within the stream to alter morphology. Habitat measurements included width, depth, substrate composition, canopy cover, and riparian land use. Trout were sampled using an electrofishing depletion method and stomach contents were obtained using a gastric lavage. Aquatic invertebrates were sampled using a Surber sampler and D-net while terrestrial invertebrates were sampled using pan traps. At the treatment site, brush bundles are already narrowing the stream while slightly increasing depth. The percentage of gravel has increased at the treatment site while the percentage of sand has decreased. Brook Trout selection of prey varied with the different types of riparian vegetation. Brook Trout in woody riparian areas feed more on terrestrial Trichopterans and Ephemeropterans while trout at grassy riparian site feed more on Ephemeroptera nymphs and terrestrial Dipterans. Selection for terrestrial invertebrates is highest during summer months and lowest during the late spring and early fall. Terrestrial invertebrate abundances are highest during the mid summer months while aquatic invertebrate abundances are highest during the late spring and early summer. The removal of Tag Alder and addition of brush bundles have begun to alter channel morphology and those changes, coupled with the alteration of riparian vegetation, may alter diets of Brook Trout.