Aquatic Sciences Meeting, Albuquerque 2001

PC10 Ecological Fluxes: Organisms, Atmospheres, Oceans, Lakes, and Rivers

Date: Wednesday, February 14, 2001

Location: Southwest Hall

Kline, T, C, PWSSC, Cordova, USA, tkline@pwssc.gen.ak.us

ASSESSING THE ROLE OF SALMON CARCASSES IN THE NITROGEN BUDGET OF SOCKEYE SALMON (ONCORHYNCHUS NERKA) NURSERY LAKES USING STABLE ISOTOPES

A model that estimates the fraction of remineralized marine-derived nitrogen (MDN) from anadromous Pacific salmon using the natural abundance of N-15/N-14 was applied to smolt data from 13 Alaskan sockeye salmon, Oncorhynchus nerka, nursery lakes. Smolt MDN ranged from near 0 to greater than 100 depending upon isotopic fractionation (IF) assumptions. For example, if IF was assumed to be high, the MDN of Karluk and Red Lakes, Kodiak Island would be > 100%. The upper and lower bounds of the model were most divergent (suggesting a maximum MDN uncertainty) at N-15/N-14 values corresponding to 100% MDN when IF is maximized. Food chain links using salmon nitrogen directly would have elevated N-15/N-14 values compared to remineralization. Therefore N-15/N-14 data will only provide qualitative assessment of MDN for direct consumers without additional diet information or a second isotopic tracer such as carbon. A watershed MDN analysis should characterize isotopically all N sources including adult salmon and have experimental controls. Sockeye salmon nursery lakes with greater dependence on salmon-derived nutrients are more likely to be candidates for overfishing-driven oligotrophication.

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Aquatic Sciences Meeting, Albuquerque 2001

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