Rates of transport of total phosphorus and total nitrogen in Mackenzie and Yukon River watersheds, N. W. T. and Y. T., Canada

Summary

Samples for particulate phosphorus (PP), particulate nitrogen (PN), total dissolved phosphorus (TDP), and total dissolved nitrogen (TDN) were taken in 1971–74 at discharge measurement stations on 11 streams and rivers in the Mackenzie River watershed, and a tributary to the Porcupine River (Yukon River watershed). Samples were taken at the point of maximum depth and velocity in the river cross section with VAN DORN samplers, by hand-filling water bottles at the river surface, or by depth-integrating water and sediment samplers. Analytical methods and precision for determinations of particulate and dissolved forms of N and P are given in Brunskill et al. (1973) and Stainton et al. (1974). Most discharge (Q) measurements were made by Water Survey of Canada (Davies 1973, 1974; Stichling 1974), but we also estimated Q in some streams, measuring velocity (with Gurley flow meters) and cross-sectional area to compute Q (see Brunskill et al. 1973). Monthly means of measured concentrations of ΣN (= TDN + PN) and ΣP (= TDP + PP) were calculated. These means were multiplied by average monthly water discharge to obtain a transport rate in moles/month. Monthly rates of transport were summed over a year to obtain annual transport rates, and were then divided by watershed area above the sampling station. These normalized transport rates, in units of moles km⁻² watershed area yr⁻¹, allow comparison between large and small rivers, and represent the flux of ΣN and ΣP from the watershed resulting from precipitation, mechanical and chemical erosion, and biological fixation and transport.