Articles | Volume 14, issue 15
Biogeosciences, 14, 3743–3762, 2017
Biogeosciences, 14, 3743–3762, 2017

Research article 15 Aug 2017

Research article | 15 Aug 2017

A global hotspot for dissolved organic carbon in hypermaritime watersheds of coastal British Columbia

Allison A. Oliver1,2, Suzanne E. Tank1,2, Ian Giesbrecht2,7, Maartje C. Korver2, William C. Floyd3,4,2, Paul Sanborn5,2, Chuck Bulmer6, and Ken P. Lertzman7,2 Allison A. Oliver et al.
  • 1University of Alberta, Department of Biological Sciences, CW 405, Biological Sciences Bldg., University of Alberta, Edmonton, AB, T6G 2E9, Canada
  • 2Hakai Institute, Tula Foundation, P.O. Box 309, Heriot Bay, BC, V0P 1H0, Canada
  • 3Ministry of Forests, Lands and Natural Resource Operations, 2100 Labieux Rd, Nanaimo, BC, V9T 6E9, Canada
  • 4Vancouver Island University, 900 Fifth Street, Nanaimo, BC, V9R 5S5, Canada
  • 5Ecosystem Science and Management Program, University of Northern British Columbia, 3333 University Way, Prince George, BC, V2N 4Z9, Canada
  • 6BC Ministry of Forests Lands and Natural Resource Operations, 3401 Reservoir Rd, Vernon, BC, V1B 2C7, Canada
  • 7School of Resource and Environmental Management, Simon Fraser University, TASC 1 – Room 8405, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada

Abstract. The perhumid region of the coastal temperate rainforest (CTR) of Pacific North America is one of the wettest places on Earth and contains numerous small catchments that discharge freshwater and high concentrations of dissolved organic carbon (DOC) directly to the coastal ocean. However, empirical data on the flux and composition of DOC exported from these watersheds are scarce. We established monitoring stations at the outlets of seven catchments on Calvert and Hecate islands, British Columbia, which represent the rain-dominated hypermaritime region of the perhumid CTR. Over several years, we measured stream discharge, stream water DOC concentration, and stream water dissolved organic-matter (DOM) composition. Discharge and DOC concentrations were used to calculate DOC fluxes and yields, and DOM composition was characterized using absorbance and fluorescence spectroscopy with parallel factor analysis (PARAFAC). The areal estimate of annual DOC yield in water year 2015 was 33.3 Mg C km−2 yr−1, with individual watersheds ranging from an average of 24.1 to 37.7 Mg C km−2 yr−1. This represents some of the highest DOC yields to be measured at the coastal margin. We observed seasonality in the quantity and composition of exports, with the majority of DOC export occurring during the extended wet period (September–April). Stream flow from catchments reacted quickly to rain inputs, resulting in rapid export of relatively fresh, highly terrestrial-like DOM. DOC concentration and measures of DOM composition were related to stream discharge and stream temperature and correlated with watershed attributes, including the extent of lakes and wetlands, and the thickness of organic and mineral soil horizons. Our discovery of high DOC yields from these small catchments in the CTR is especially compelling as they deliver relatively fresh, highly terrestrial organic matter directly to the coastal ocean. Hypermaritime landscapes are common on the British Columbia coast, suggesting that this coastal margin may play an important role in the regional processing of carbon and in linking terrestrial carbon to marine ecosystems.

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Short summary
Rivers draining small watersheds of the outer coastal Pacific temperate rainforest export some of the highest yields of dissolved organic carbon (DOC) in the world directly to the ocean. This DOC is largely derived from soils and terrestrial plants. Rainfall, temperature, and watershed characteristics such as wetlands and lakes are important controls on DOC export. This region may be significant for carbon export and linking terrestrial carbon to marine ecosystems.
Final-revised paper