Nutrient additions to mitigate for loss of Pacific salmon: consequences for stream biofilm and nutrient dynamics

Ecosphere
By: , and 

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Abstract

Mitigation activities designed to supplement nutrient and organic matter inputs to streams experiencing decline or loss of Pacific salmon typically presuppose that an important pathway by which salmon nutrients are moved to fish (anadromous and/or resident) is via nutrient incorporation by biofilms and subsequent bottom-up stimulation of biofilm production, which is nutrient-limited in many ecosystems where salmon returns have declined. Our objective was to quantify the magnitude of nutrient incorporation and biofilm dynamics that underpin this indirect pathway in response to experimental additions of salmon carcasses and pelletized fish meal (a.k.a., salmon carcass analogs) to 500-m reaches of central Idaho streams over three years. Biofilm standing crops increased 2–8-fold and incorporated marine-derived nutrients (measured using 15N and 13C) in the month following treatment, but these responses did not persist year-to-year. Biofilms were nitrogen (N) limited before treatments, and remained N limited in analog, but not carcass-treated reaches. Despite these biofilm responses, in the month following treatment total N load was equal to 33–47% of the N added to the treated reaches, and N spiraling measurements suggested that as much as 20%, but more likely 2–3% of added N was taken up by microbes. Design of biologically and cost-effective strategies for nutrient addition will require understanding the rates at which stream microbes take up nutrients and the downstream distance traveled by exported nutrients.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Nutrient additions to mitigate for loss of Pacific salmon: consequences for stream biofilm and nutrient dynamics
Series title Ecosphere
DOI 10.1890/ES13-00366.1
Volume 5
Issue 6
Year Published 2014
Language English
Publisher Ecological Society of America
Publisher location Washington, D.C.
Contributing office(s) Coop Res Unit Seattle
Description 23 p.
First page 1
Last page 22
Country United States
State Idaho
Other Geospatial North Fork Boise River
Online Only (Y/N) N
Additional Online Files (Y/N) N