Habitat evaluation of wadeable streams based on accepted protocols provides a rapid and widely used adjunct to biological assessment. However, little effort has been devoted to habitat evaluation in non-wadeable rivers, where it is likely that protocols will differ and field logistics will be more challenging. We developed and tested a non-wadeable habitat index (NWHI) for rivers of Michigan, where non-wadeable rivers were defined as those of order >or=5, drainage area >or=1600 km2, mainstem lengths >or=100 km, and mean annual discharge >or=15 m3/s. This identified 22 candidate rivers that ranged in length from 103 to 825 km and in drainage area from 1620 to 16,860 km2. We measured 171 individual habitat variables over 2-km reaches at 35 locations on 14 rivers during 2000-2002, where mean wetted width was found to range from 32 to 185 m and mean thalweg depth from 0.8 to 8.3 m. We used correlation and principal components analysis to reduce the number of variables, and examined the spatial pattern of retained variables to exclude any that appeared to reflect spatial location rather than reach condition, resulting in 12 variables to be considered in the habitat index. The proposed NWHI included seven variables: riparian width, large woody debris, aquatic vegetation, bottom deposition, bank stability, thalweg substrate, and off-channel habitat. These variables were included because of their statistical association with independently derived measures of human disturbance in the riparian zone and the catchment, and because they are considered important in other habitat protocols or to the ecology of large rivers. Five variables were excluded because they were primarily related to river size rather than anthropogenic disturbance. This index correlated strongly with indices of disturbance based on the riparian (adjusted R2 = 0.62) and the catchment (adjusted R2 = 0.50), and distinguished the 35 river reaches into the categories of poor (2), fair (19), good (13), and excellent (1). Habitat variables retained in the NWHI differ from several used in wadeable streams, and place greater emphasis on known characteristic features of larger rivers.
We investigated functional and structural responses of periphyton communities to simulated nonpoint source (NPS) pollution over a 2-year period. Periphyton communities were examined in three unique but hydrologically connected habitats in the lower Muskegon River: river, wetland, and lake. Our study addressed several major questions:(1) what are the effects of nonpoint source pollutants on periphyton structure and function, (2) to what degree do environmental conditions, including the pollutant delivery system and hydrologic conditions, affect periphyton response, and (3) do periphyton communities show synchronous responses to nonpoint source pollution? Nutrients were added over a 21-day period in each of the four seasons over 2 years. The effect of road salt on metabolism was evaluated in the winter and spring seasons in the river habitat only. In general, the periphyton community showed complex responses to the NPS amendments, but there was little evidence of nutrient limitation in this system based on community structure, biomass accrual, metabolism, or alkaline phosphatase activity. This result was unexpected given the relatively low ambient concentrations of phosphorus. We discuss the possibilities that nutrient delivery was ineffective or that herbivory and/or irradiance might have constrained periphyton growth, but ultimately conclude that our results suggest that periphyton communities in the lower Muskegon River watershed were (1) nutrient-replete, (2) tolerant of short-term salt additions, and (3) influenced more by local conditions (habitat) than by regional (watershed) factors. In systems where nonpoint source pollutant delivery is diffuse and hydrologic residence time is short, the influence of nonpoint source pollutants on periphyton may be either modest or too difficult to detect using traditional endpoints.
A 3-year study (2000-2002) in southeastern Wisconsin was conducted to assess the effects of Bacillus sphaericus applied for mosquito control on nontarget wetland invertebrates. The experimental design consisted of control and treatment sites (that were applied by helicopter with Vectolex CG), each in 2 vegetation habitat types: reed canary grass marsh (Phalaris arundinacea) and cattail marsh (Typha spp.). In each of these areas, a predetermined number of timed (30-sec) D-frame aquatic net samples containing vegetation, detritus, and invertebrates were collected 1 day before spraying and 72 h after spraying to detect for effects. We examined and compared 5 bioassessment measures to determine if there was an effect of B. sphaericus on nontarget organisms during each of the sampling years. The metrics tested were (1) mean taxa richness (the mean number of all taxa), (2) mean diversity (combines taxa richness and abundances in a summary statistic; i.e., Shannon Index [H'I]), (3) Diptera richness (minus mosquitoes) as a proportion of all other taxa richness (Diptera/others richness), (4) Diptera abundance (minus mosquitoes) as a proportion of all other invertebrate abundance (Diptera/others abundance), and (5) functional group changes in percent collector-gatherers, collector-filterers, scrapers, shredders, and predators. When Vectolex was applied during 6 treatments at the labeled dosage rate in the above habitats in Brookfield, WI, no detrimental effects to nontarget organisms could be attributed to this microbial insecticide. Much of the variation in the control vs. treatment and pre vs. post plots was attributed to factors other than the effects of B. sphaericus on nontarget organisms, such as the time of sampling, natural variation that occurs in such diverse habitats as canary grass and cattail marshes, and water depth, which varied among years.
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