Tuesday, May 19, 2009

Nutrient limitation and uptake response to experimental salmon additions in Idaho headwater streams

Rebecca A. Martin1, Amy M. Marcarelli1, Colden V. Baxter1, Scott F. Collins1, and Mark S. Wipfli2. (1) Stream Ecology Center, Department of Biological Sciences, Idaho State University, Pocatello, ID 83202-8007, (2) U.S. Geological Survey, University of Alaska Fairbanks, Alaska Cooperative Fish and Wildlife Research Unit, Institute of Arctic Biology, Fairbanks, AK 99775

Anadromous salmon were historically an important nutrient source for Northwest streams, and the decline of salmon returns to nutrient-poor streams may have important ecosystem effects.  Our objective was to determine how in-stream nutrient limitation and processing responded to two different mitigation tools for nutrient loss – salmon carcasses and analog (pelletized salmon).  We conducted an experiment in the Boise River basin in Idaho, with three tributaries receiving carcass additions, three receiving analog, and three reference streams with no additions.  Two weeks following the additions, nutrient diffusing substrates indicated that stream biofilms were nitrogen (N) limited in both the control and analog streams; however, we observed no nutrient limitation in carcass streams.  Additionally, short-term N-NO3- additions in one set of experimental streams revealed that N demand relative to availability (uptake velocity; v) was similar between the analog and the reference stream; the carcass stream showed no net N uptake.  Although carcasses and analog have similar N:P ratios, there may be differences in nutrient forms or concentrations released from the two treatments.  Our results suggest that salmon carcasses and analog produce different nutrient limitation and recycling efficiencies in these streams, and therefore may not be exchangeable mitigation techniques for nutrient loss.