Salmon influences on dissolved organic matter in a coastal temperate brownwater stream: An application of fluorescence spectroscopy

Abstract

We examined how spawning Pacific salmon (genus Oncorhynchus) affect streamwater concentrations of inorganic nitrogen and phosphorus and dissolved organic matter in Peterson Creek, a stream in southeast Alaska. When spawning salmon were present, concentrations of ammonium (NH 4 -N) increased by more than 100 times over prespawning levels and concentrations of soluble reactive phosphorus increased by more than an order of magnitude. In contrast, concentrations of nitrate (NO 3 -N) increased by only two to three times during spawning and were not significantly higher than at an upstream reference site with no salmon. During spawning, concentrations of dissolved organic carbon and dissolved organic nitrogen were significantly higher in the spawning reach compared with the upstream reference site. The influx of salmon-derived dissolved organic matter (DOM) altered the fluorescence index (FI), which has previously been used to distinguish between terrestrial and aquatic sources of DOM, with the FI increasing significantly during the salmon run. Salmon DOM was rich in protein compared with the DOM derived from the terrestrial portion of the watershed. Spawning salmon may be an important source of labile DOM in Peterson Creek.

Source, biogeochemical cycling, and fluorescence characteristics of dissolved organic matter in an agro‐urban estuary

“…Fluorescence characterization of DOM and PARAFAC modeling-We measured fluorescence EEMs of DOM on a Varian Cary Eclipse fluorometer with a 1-cm quartz cuvette following the procedures of Hood et al (2007). The EEMs were created on filtered water samples at room temperature by measuring fluorescence intensity across excitation wavelengths ranging from 240 nm to 450 nm (5-nm increments) and emission wavelengths ranging from 300 nm to 600 nm (2-nm increments).…”

Fluorescence characteristics and biodegradability of dissolved organic matter in forest and wetland soils from coastal temperate watersheds in southeast Alaska

“…Samples were allowed to warm to room temperature, analyzed on a Genesys 5 spectrophotometer and SUVA 254 was calculated as the UV absorbance at 254 nm per l mg-C ¡1 m ¡1 . Fluorescence excitationemission matrices (EEM) of DOM were measured on a Fluoromax-3 (Jobin Yvon Horiba) Xuorometer with a xenon lamp following the procedures of Hood et al (2007). EEMs were created by measuring Xuorescence intensity across excitation wavelengths ranging from 240-450 nm and emission wavelengths ranging from 300-600 nm.…”

Biophysical controls on dissolved organic carbon concentrations of Alaskan coastal temperate rainforest streams

“…Our results suggest that, although salmon carbon inputs may be high in some locations, there is no unambiguous impact of salmon carbon on stream DOC concentration at larger scales. High spawner densities and low discharge can increase stream DOC concentrations during spawning (Hood et al 2007), but there is little evidence that the phenomenon is widespread or persistent (Janetski et al 2009). Invoking salmon carbon inputs to explain the increased concentrations at low wetland coverage would not explain how salmon inputs could simultaneously reduce concentrations at higher wetland abundances.…”

“…Given the abundance of carbon and wetlands in the PCTR, the primary source of DOC transported through streams to the ocean is likely wetlands. However, although wetlands may contribute significantly to DOC production, other factors may influence DOC concentration such as varying forest stand ages, structures related to windthrow, timber harvest, and the input of carbon from millions of spawning salmon (Nowacki and Kramer 1998;Caouette et al 2000;Nowacki et al 2001;Hood et al 2007). The vast expanse of the Alaska PCTR is an excellent template to test the strength of association between the extent of wetlands within a watershed and DOC concentration in streamwater and develop quantitative predictive relationships for the diverse landscape components of the region.…”