Stream ecosystem research in a watershed perspective

In has now become increasing clear that characteristics of stream ecosystems are inti-mately tied to the nature of their watershed (HYNES 1975). Until recently, however, researchdirected at stream ecosystems was largely confined to individual segments or small water-sheds, seldom being extrapolated to a wider perspective. Due primarily to the pioneeringwork of VANNOTE et al. (1980), research on lotic ecosystems has recently shifted fromstudies of stream segments to studies of biological and physical longitudinal profiles asstreams gradually coalesce to form large rivers (see for example, SEDELL et al. 1978; NAI-MAN & SEDELL 1979 a, b, 1980). This river continuum concept may be referred to as a"second dimension" in our understanding of the characteristics of streams as they flowfrom headwaters to the sea. Research on lotic ecosystems is now on the verge of progressingto a "third dimension", by giving breadth to the previous studies of longitudinal changes,through careful watershed analyses of stream size, length, numbers, discharge, and gradientwithin the entire drainage network.
Gross physical analyses of large watersheds are relatively easy to accomplish, and whencombined with studies of stream segments of various orders, can be a powerful tool forunderstanding the basic structural and functional processes of large and seemingly complexecosystems. When physical and biological studies are combined, the relative importance,abundance, activity, and distribution of biological components can be readily examined atthe watershed level. By not considering the entire watershed, overemphasis is often placed
on certain aspects relative to their proportion within the watershed, both in terms ofquantity and quality. As a consequence, longitudinal and latitudinal perspective, whichcovers the total drainage network, is lost.
For this short paper we have chosen three examples from our studies in Quebec,Canada, and Washington, U. S. A., to demonstrate how physical analyses can be combinedwith biological studies to produce a clearer understanding of large watershed ecosystems.These examples include export of organic carbon, distribution of periphyton production,and the relative abundance and distribution of quality habitat for salmonid fishes.