The Annual Pattern and Spatial Distribution of Aquatic Oxygen Metabolism in Boreal Forest Watersheds

Abstract

The level and diversity of metabolism in lotic ecosystems are largely functions of channel geomorphology and hydrology, making site—specific studies difficult to extrapolate to other parts of the watershed. This paper describes the pattern and distribution of aquatic oxygen metabolism for undisturbed boreal forest watersheds in eastern Quebec, Canada. Metabolism by periphyton, mosses, macrophytes, fine particulate organic matter (FPOM: 0.5 μm—1mm), an coarse particulate organic matter (CPOM: >1mm) was examined during the ice—free period (April to November) of 1979 and 1980 in First Choice Creek (first order; watershed area: 0.25 km 2), Beaver Creek (second order; 1.83 km 2), Muskrat River (fifth order; 207 km 2), matamek River (sixth order; 673 km 2), and the Moisie River (ninth order; 19 871 km 2). As watershed area increases, primary production and the number of autotrophic groups are augmented with moss and macrophyte communities. Total O 2 metabolism increases downstream, ranging from <1 g°m—2°d—1 in First Choice Creek nearly 5 g°m—2°d—1 during summer in the Moisie River. Autotrophic metabolism is not normally correlated with light or chlorophyll, but annual O 2 production is highly correlated with stream order (r 2 > .76 in most cases). These data are combined with a geomorphological analysis of the watershed to discern the spatial distribution of aquatic metabolism, and to estimate total aquatic metabolism in the Moisie River drainage network. Mosses, occurring only in streams of fourth or higher order, are the most productive autotrophic component in the watershed (3.9 x 10 10 g/yr); by comparison, periphyton produce only 2.1 x 10 10 g/yr. FPOM is the most active detrital component (6.6 x 10 10 g/yr). Geomorphic analyses show that streams of fourth or higher order comprise only 1.2% of the total number and 12.7% of the total length, but have 76.8% of the lotic surface area, and are responsible for 86.3% of the gross production by the entire lotic drainage network. The surface area of lakes is approximately six times that of streams, but their contribution (phytoplankton) to total aquatic ecosystem metabolism is comparable only to that of lotic periphyton. Results demonstrate that the River Continuum Concept can be extended to the watershed level by combining biological measurement with geomorphological analyses of the drainage network, thus allowing a detailed description of spatial and temporal patterns for specific metabolic components and total ecosystem metabolism to be constructed.