INTRODUCTION

Surface waters are the receiving environment for all activities within a catchment, and integrate processes across temporal and spatial scales. Estimates suggest that the rate of loss of freshwater species is five times that of species in temperate terrestrial environments, and rivals the rate found in tropical forests (Revenga et al. 2005). Threats to aquatic ecosystems come from a wide variety of land uses, including agriculture, urbanization, mining, forestry, impoundment, and others. Efforts to protect important characteristics of freshwater environments focus on physical and chemical aspects, such as water quality, temperature, channel bedforms, and instream flow needs. The conservation of fish (with a predominant focus on salmonids in northern temperate regions) and protection of aquatic biodiversity in general are often assumed to be served by this focus on the abiotic subsystem.

In forested ecosystems, sustainability of aquatic ecosystem values has been the subject of an enormous effort to determine what land-use practices most affect these systems, and how those impacts might be mitigated (Bormann et al. 1974; McEachern et al. 2006; Prepas et al. 2006; Richardson 2008). The specific mechanisms by which land uses, such as forestry, affect catchments often interact with each other along multiple pathways, for instance concomitant changes in light regimes, temperature, wood and organic matter inputs, etc. (Richardson and Danehy 2007; Thompson et al. 2008). Measures to conserve biodiversity and other ecosystem services need to consider the non-independence of these multiple processes.