Salmon influences on dissolved organic matter in a coastal temperate brown-water stream: an application of fluorescence spectroscopy.

Abstract

The annual return of spawning Pacific salmon (genus Oncorhynchus) can have a dramatic effect on the nutrient budgets of recipient freshwater ecosystems. We examined how spawning salmon affect streamwater concentrations of inorganic nitrogen and phosphorus and dissolved organic carbon (DOC) in Peterson Creek, a salmon stream in southeast Alaska. In the presence of spawning salmon, concentrations of ammonium (NH₄-N) increased by more than 100 times and concentrations of soluble reactive phosphorus (SRP) increased by more than an order of magnitude. In contrast, concentrations of nitrate (NO₃-N) increased by only 2 to 3 times during spawning and were not significantly higher than at an upstream control site with no salmon. Concentrations of DOC were significantly higher in the presence of salmon, and the influx of salmon-derived dissolved organic matter (DOM) altered the fluorescence properties of DOM in Peterson Creek. The fluorescence index, which has previously been used to distinguish between terrestrial and aquatic sources of DOM, increased significantly during the salmon run. Additionally, three-dimensional fluorescence excitation-emission matrices (EEMs) showed that salmon DOM was rich in protein compared to the DOM derived from the terrestrial portion of the watershed. These findings suggest that spawning salmon may be an important source of labile DOM in Peterson Creek and further that fluorescence spectroscopy is an effective tool for identifying and characterizing salmon DOM within the larger streamwater DOM pool.

Citation

Hood, E.; Fellman, J.; Edwards, R.T. 2007. Salmon influences on dissolved organic matter in a coastal temperate brown-water stream: an application of fluorescence spectroscopy. Limnology and Oceanography. 52(4): 1580-1587