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Presented at the NABS Annual meeting, Vancouver, British Columbia, 2004
in Periphyton
Responses of periphyton and benthic macroinvertebrates to experimental additions of nitrogen and phosphorus in a mesocosm study
G.M. Hoyle1, J.H. Braatne2, and K.I. Ashley3. 1Kootenai Tribe of Idaho, Fish and Wildlife Department, Bonners Ferry, ID, USA, 2Department of Fish and Wildlife Resources, University of Idaho, Moscow, ID, USA, 3Fisheries Centre, University of British Columbia, Vancouver, BC, CANADA
The Kootenai River in Idaho is nutrient-depleted due to extensive river diking, channelization, impoundments and isolation/drainage of floodplain wetlands. Whole-river fertilization has recently been proposed to restore river productivity and native fish populations. Based on theoretical concepts of nutrient co-limitation, responses of naturally-colonizing periphyton and benthic macroinvertebrates to experimental additions of both N and P were assessed in a river mesocosm study. Treatment effects were 1.5 mg l-1 P ± 30 mg l-1 N, 3.0 mg l-1 P, 5.0 mg l-1 P ± 30 mg l-1 N.
Algal biomass and benthic macroinvertebrate density increased at higher P concentrations, particularly in relation to elevated N concentrations. There were prominent shifts in algal and macroinvertebrate taxa with nutrient addition. Blue-green and green algae were the dominant taxa at higher P and N concentrations, resulting in extensive periphyton blooms. Mayfly density progressively declined and chironomids density increased in response to these shifts in algal taxa. Yet, these growth responses should be anticipated in only select reaches of the Kootenai River. Given complex interactions between nutrients and fluvial geomorphology inherent to large alluvial rivers, additional studies will be required before undertaking large-scale fertilization of the Kootenai River.
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