LAND-USE EFFECTS ON HABITAT, WATER-QUALITY, PERIPHYTON, AND BENTHIC INVERTEBRATES IN WAIKATO, NEW-ZEALAND, HILL-COUNTRY STREAMS

Water quality, habitat, and biota were compared during spring amongst c. 100 m reaches on 11 streams draining pasture, native (podocarp-broa dleaf) forest, and exotic pine forest established on pasture 15 years previously. Differences were greatest between the pasture and native f orest streams. Only 1-3% of incident light reached native and pine for est streams whereas 30% reached pasture streams. Pasture streams had 2 .2 degrees C higher mean temperature than the native streams, and 5-fo ld higher nitrate, 30-fold higher algal biomass, and Ii-fold higher gr oss photosynthesis. Native streams were 60% wider than pasture, with p ine streams intermediate. Pine and pasture streams had 3-fold higher s uspended solids and fine sediment stored in the streambed than native streams. Woody debris volume was 17-fold greater in pine than pasture streams, with native streams intermediate. Invertebrate taxa richness did not differ between land uses. Community composition differed most between pasture and native forest, with pine forest streams intermedia te. Invertebrate densities were 3-fold higher in pasture than native s treams, mainly because of more chironomids and snails, but mayflies, s toneflies, and caddisflies densities were 2-3-fold higher in forest st reams than pasture.