MOUNTAIN STREAMS IN WESTLAND, NEW-ZEALAND - BENTHIC ECOLOGY AND MANAGEMENT ISSUES

1. The West Coast of the South Island, New Zealand (Westland) is a reg ion of mountains, forests, high rainfall, and a history of exploitatio n. The Southern Alps rise to over 3000 m in the east of the region, an d a narrow coastal plain supports some agriculture and the main centre s of population. 2. Stream waters in the Southern Alps are characteriz ed by low concentrations of major ions, and most can be described as c alcium-sodium-bicarbonate waters. Brown waters with low pH and high co ncentrations of dissolved organic carbon are common at low and interme diate altitudes. 3. Many mountain streams and rivers provide physicall y harsh environments for aquatic biota with their rapidly changing flo ws and frequent spates. Hydrological factors and low nutrient concentr ations limit periphyton standing crops, and biomass of coarse detritus is often low. Invertebrate populations are usually dominated by insec t larvae that feed primarily on FROM and stone surface biofilms. 4. Fe atures of the macroinvertebrate stream fauna on the West Coast are the wide range of physicochemical conditions tolerated by many common spe cies, and the numerical dominance of the mayfly Deleatidium (Leptophle biidae) in many streams. The Plecoptera also exhibit high diversity re lative to other parts of the country, and an unusual trend towards ter restrialism is shown by larvae of Gripopterygidae. 5. The West Coast h as a long history of coal and gold mining, forestry and fanning, activ ities that have had negative impacts on stream communities and water q uality. We discuss some ecological and management issues associated wi th present day mining practices, and a proposal to take large volumes of alpine stream water for export.