Articles | Volume 12, issue 19
Biogeosciences, 12, 5597–5618, 2015
Biogeosciences, 12, 5597–5618, 2015

Research article 01 Oct 2015

Research article | 01 Oct 2015

Seasonal hydrology drives rapid shifts in the flux and composition of dissolved and particulate organic carbon and major and trace ions in the Fraser River, Canada

B. M. Voss1,2,a, B. Peucker-Ehrenbrink1,3, T. I. Eglinton4, R. G. M. Spencer5,6, E. Bulygina6, V. Galy1, C. H. Lamborg1,7, P. M. Ganguli1, D. B. Montluçon4, S. Marsh3, S. L. Gillies3, J. Fanslau1,3,6, A. Epp1,3, and R. Luymes1,3 B. M. Voss et al.
  • 1Woods Hole Oceanographic Institution, 360 Woods Hole Road, Woods Hole, MA 02543, USA
  • 2Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
  • 3University of the Fraser Valley, 33844 King Road, Abbotsford, BC V2S 7M7, Canada
  • 4Eidgenössische Technische Hochschule, Sonneggstrasse 5, 8092 Zürich, Switzerland
  • 5Florida State University, 600 West College Avenue, Tallahassee, FL 32306, USA
  • 6Woods Hole Research Center, 149 Woods Hole Road, Falmouth, MA 02540, USA
  • 7University of California Santa Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
  • anow at: US Geological Survey, 3215 Marine Street, Suite E-127, Boulder, CO 80303, USA

Abstract. Rapid changes in the volume and sources of discharge during the spring freshet lead to pronounced variations in biogeochemical properties in snowmelt-dominated river basins. We used daily sampling during the onset of the freshet in the Fraser River (southwestern Canada) in 2013 to identify rapid changes in the flux and composition of dissolved material, with a focus on dissolved organic matter (DOM). Previous time series sampling (at twice monthly frequency) of dissolved inorganic species in the Fraser River has revealed smooth seasonal transitions in concentrations of major ions and tracers of water and dissolved load sources between freshet and base flow periods. In contrast, daily sampling reveals a significant increase in dissolved organic carbon (DOC) concentration (200 to 550 μmol L−1) occurring over a matter of days, accompanied by a shift in DOM optical properties, indicating a transition towards higher molecular weight, more aromatic DOM composition. Comparable changes in DOM composition, but not concentration, occur at other times of year, underscoring the role of seasonal climatology in DOM cycling. A smaller data set of total and dissolved Hg concentrations also showed variability during the spring freshet period, although dissolved Hg dynamics appear to be driven by factors beyond DOM as characterized here. The time series records of DOC and particulate organic carbon (POC) concentrations indicate that the Fraser River exports 0.25–0.35 % of its annual basin net primary productivity. The snowmelt-dominated hydrology, forested land cover, and minimal reservoir impoundment of the Fraser River may influence the DOC yield of the basin, which is high relative to the nearby Columbia River and of similar magnitude to that of the Yukon River to the north. Anticipated warming and decreased snowfall due to climate changes in the region may cause an overall decrease in DOM flux from the Fraser River to the coastal ocean in coming decades

Short summary
This study presents seasonal cycles of organic matter concentration and composition in the Fraser River. Dissolved organic matter patterns are linked to flushing of shallow soil layers during spring snowmelt and fall rain events. The preliminary Hg data set indicates significant changes in concentrations during the spring freshet. Organic carbon export, as both area-normalized yield and the proportion of basin primary productivity, in the Fraser River is typical of large rivers globally.
Final-revised paper