Catchment-scale analysis of aquatic ecosystems

Aquatic ecologists have a rich history of including a or streamside corridor obviously is important; the land–water interface, or ecotone (Naiman & Décamps, landscape perspective in theories about lakes and 1990), directly influences critical processes such as rivers. Position in the landscape and underlying geoorganic matter inputs, shade and nutrients (Sweeney, logy provided critical insights into differences among 1992; Osborne & Kovacec, 1993). But the entire catchlake types that led to the formation of lake trophic ment also influences the rivers and lakes within its classification (Wetzel, 1983). Comparative studies of boundaries, via larger-scale controls on chemistry, multiple lakes within a single lake district lent much hydrology and sediment delivery. The landscape impetus to the development of limnology since the influences its water bodies through multiple pathways early twentieth century (Pearsall, 1930; Macan, 1970), and mechanisms, operating at different spatial scales, and continues to be a useful approach to this day and at present there is only a limited understanding (Schindler et al., 1990). Early studies of riverine systems of how these inter-relate. A spatial conceptualization emphasized physical and biological changes that of aquatic ecosystems suggests a hierarchical organizaoccurred along a river’s course (Huet, 1949; Illies & tion of physical units, perhaps most clearly captured Botosaneanu, 1963), leading to the formulation of the for rivers in the hierarchy: habitat–reach–segment– River Continuum Concept (Vannote et al., 1980), the subcatchment–basin (Frissell et al., 1986; Hawkins template of which is longitudinal position. Some 20 et al., 1992), and in the nested classification of stream years ago, Hynes (1975) synthesized then current order (Strahler, 1964). Allan, Erickson & Fay (1997) knowledge of landscape–stream interactions to argue and Johnson & Covich (1997) point out that particular with lasting effect that, ‘in every respect, the valley mechanisms of landscape–freshwater interactions rules the stream’. Investigations of the land–water operate at different scales. For example, inputs of ecotone continue to progress on these firm foundacoarse particulate organic matter depend upon local, tions. The field gains new impetus from the growing streamside vegetation, whereas hydrologic regime realization that large-scale, human alteration of land(which affects sediment delivery and channel condiscapes has widespread implications (generally negations) is the product of regional climate, geology and tive) for the well-being of aquatic ecosystems (Naiman vegetation. Whether and how these processes might et al., 1995). On a positive note, however, technical and be hierarchically structured requires much more conceptual advances continue to improve our ability investigation across multiple spatial scales. to study and understand the linkages between landscapes and freshwater ecosystems. The following series of papers addresses such issues and points to Tools and approaches future directions for this important area of inquiry. A focus on the influence of the landscape on riverine Spatial analysis takes place as an almost subconscious and lake ecosystems leads quickly to questions regardactivity whenever we gaze across a landscape from ing the appropriate scale of investigation (Levin, 1992), some vantage point. However, geographical information systems (GIS) and image processing (IP) together and ultimately, of management as well. The riparian