INTRODUCTION

To understand the ecology of streams it is vital to appreciate the links within and between aquatic habitats and the landscape of which they are part. Many of the problems of poor land management stem from ignorance of the interactive nature of ecosystems and from a lack of appreciation of the scales at which such interactions operate. Human-induced changes can disrupt or override natural processes. The goal of contemporary land and water resource managers is to manage landscapes in an ecologically sustainable way. However, in the past, management has focussed most on the need to provide raw materials, food and fibre, as well as land and water for urban and industrial development. Socio-economic pressures towards development have resulted in widespread perturbations to aquatic ecosystems and irreversible degradation in many of them. The continuing broad-scale conversion of natural vegetation and landscape into forestry, agriculture, water storage or other land uses has dramatic effects on the ecology of streams. Impacts vary with the extent of the conversion relative to the size of the catchment, the nature of the new land use, land management under the new land use, the climate, and the extent of riparian and contiguous buffer zones. Generalisations regarding these effects are difficult because of this diversity, which creates a complex array of environmental conditions.

The increasing awareness of the considerable threats to natural aquatic environments and of their importance to human life and livelihood has shifted attention to include not only water supplies but also to ensure the maintenance of good water quality, river health and ecological processes.