Characteristics of Sediment and Organic Carbon Export from Pristine Boreal Forest Watersheds

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Author: Naiman, Robert J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1982
• Subjects: Aquatic Science; Ecology, Evolution, Behavior and Systematics; Beaver Creek
• Online Access: http://dx.doi.org/10.1139/f82-226; http://www.nrcresearchpress.com/doi/pdf/10.1139/f82-226

Estimates of the amount of material moving annually from terrestrial ecosystems to the ocean are largely based on an incomplete understanding of events occurring throughout the hydrologic year, and only a vague comprehension of in-stream processes controlling that export. Discharge, suspended sediment, particulate organic matter (POM; > 0.5 μm), dissolved organic carbon (DOC; <0.5 μm diameter), and the percentage of organic matter were measured from 1979 to 1981 in five pristine Quebec streams: First Choice Creek (1st order; watershed area: 0.25 km 2 ), Beaver Creek (2nd order; 1.83 km 2 ), Muskrat River (5th order; 204 km 2 ), Matamek River (6th order; 673 km 2 ), and the Moisie River (9th order; 19 871 km 2 ). All streams, with the exception of First Choice Creek, have a strong spring freshet when 43–55% of the annual discharge occurs. By describing sediment and organic carbon export throughout the annual hydrologic cycle, 1 showed that during the 2-mo spring freshet 71–92% of the annual sediment load is exported but only 59–65% of the annual POM load, and only 47–51% of the annual DOC load. Sediment yield is relatively constant between watersheds (1.5–7.6 g∙m −2 ∙yr −1 ), as is POM export (1.0–6.7 g ash-free dry-weight [AFDW]∙m −2 ∙yr −1 ); however, export DOC varies from 3.1 g C∙m −2 ∙yr −1 in First Choice Creek to 48.4 g C∙m −2 ∙yr −1 in Beaver Creek. There appears to be rapid loading of carbon between 1st- and 2nd-order streams in boreal forests, followed by biological and physical processing as watershed area increases. Thus, for the Moisie River watershed, export of total organic carbon (TOC) is reduced to only 4.7 g C∙m −2 ∙yr −1 . Export of coarse particulate organic matter (> 1 mm) is negligible (normally < 0.1 mg∙L −1 ), as is oxidation of the suspended load (< 0.5%∙d −1 ). Effects of summer storms, natural diel variations, and depth of sample from the water column are shown to have a minimal influence on concentrations. Rating curves (kg∙d −1 vs. discharge) are developed to estimate ...