Mountain streams in Westland, New Zealand: benthic ecology and management issues

SUMMARY 1. The West Coast of the South Island, New Zealand (Westland) is a region of mountains, forests, high rainfall, and a history of exploitation. The Southern Alps rise to over 3000m in the east of the region, and a narrow coastal plain supports some agriculture and the main centres of population. 2. Stream waters in the Southern Alps are characterized by low concentrations of major ions, and most can be described as calcium—sodium—bicarbonate waters. Brown waters with low pH and high concentrations of dissolved organic carbon are common at low and intermediate altitudes. 3. Many mountain streams and rivers provide physically harsh environments for aquatic biota with their rapidly changing flows and frequent spates. Hydrological factors and low nutrient concentrations limit periphyton standing crops, and biomass of coarse detritus is often low. Invertebrate populations are usually dominated by insect larvae that feed primarily on FROM and stone surface biofilms. 4. Features of the macroinvertebrate stream fauna on the West Coast are the wide range of physicochemical conditions tolerated by many common species, and the numerical dominance of the mayfly Deleatidium (Leptophlebiidae) in many streams. The Plecoptera also exhibit high diversity relative to other parts of the country, and an unusual trend towards terrestrialism is shown by larvae of Gripopterygidae. 5. The West Coast has a long history of coal and gold mining, forestry and farming, activities that have had negative impacts on stream communities and water quality. We discuss some ecological and management issues associated with present day mining practices, and a proposal to take large volumes of alpine stream water for export.