| |
Presented at the NABS Annual meeting, Anchorage, Alaska, 2006
in Flow of Resources to and from Freshwater Ecosystems 3
Marine-derived nutrients and ecosystem metabolism: reconsidering what salmon do to streams
G.W. Holtgrieve, D.E. Schindler, and S.R. Alin.University of Washington, Seattle, WA 98105
Spawning anadromous salmon are a subsidy of nutrients, organic matter, and energy to freshwater and riparian ecosystems. It has been widely hypothesized that salmon-derived nutrients fertilize streams, increasing net primary productivity with benefits propagating throughout the ecosystem. However, this hypothesis remains untested at the ecosystem scale. In addition, much less attention has been given to the effects of salmon spawning activities and carcass decay on ecosystem respiration. We investigated how salmon influence ecosystem metabolism by measuring the concentration and isotopic composition of dissolved O2 and CO2 over the course of the open water season in Pick Creek, SW Alaska. During salmon spawning O2 concentration declined by 30% from pre-spawning levels while CO2 concentration roughly doubled. 18O: 16O of dissolved O2 indicated the stream to be net autotrophic before the arrival of salmon but changing to net heterotrophic with substantial respiration after salmon. Pre-salmon isotopic composition of dissolved CO2 (DI13C) showed the source of carbon to be atmospherically-derived. After salmon spawning dissolved CO2 was of marine origin. The presence of salmon in this stream therefore reverses the overall metabolic state of the system and potential benefits from productivity enhancement from fertilization are likely offset by substantial heterotrophic respiration.
|
|
