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-broadleaf) forest, and exotic pine forest established on pasture 15 years previously. Differences were greatest between the pasture and native forest streams. Only 1-3% of incident light reached native and pine forest streams whereas 30% reached pasture streams. Pasture streams had 2.2 degrees C higher mean temperature than the native streams, and 5-fold higher nitrate, 30-fold higher algal biomass, and Ii-fold higher gross photosynthesis. Native streams were 60% wider than pasture, with pine streams intermediate. Pine and pasture streams had 3-fold higher suspended 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 intermediate. Invertebrate densities were 3-fold higher in pasture than native streams, mainly because of more chironomids and snails, but mayflies, stoneflies, and caddisflies densities were 2-3-fold higher in forest streams than pasture.