2006/01/01 by Stephanie M. Parkyn, Parkyn, Stephanie M., Davies-Colley, Rob J. +5
Environmental Science · #Freshwater macroinvertebrate diversity and ecology #Soil and Water Nutrient Dynamics #Hydrology and Sediment Transport Processes
paper · pdf · doi:10.26021/494
Environmental conditions in streams draining pastoral catchments are typically degraded by comparison with native forest streams. However, few studies have investigated land-use influences on streams in erosion-prone terrain where channel disturbance and mobilisation of land contaminants under pasture might be particularly severe. We studied the water quality and stream ecological ‘health’ of streams in two catchments in the Gisborne District, eastern North Island, New Zealand, where pine afforestation is proceeding rapidly in an effort to reduce erosion. We compared pasture, pine plantation, and native forest land-uses in these catchments that were characterised by differing forms of erosion of the soft rock hill country. Streams in mature pine plantations in both catchments had generally better water quality (lower faecal contamination and nutrient concentrations) than those in pasture, and tended to approach the condition of reference streams in native forest. However, visual clarity and turbidity and particulate forms of nutrients remained degraded in pine plantations where deeply incised gullies continued to yield large amounts of fine sediment. Stream stability had the dominant influence on epilithon biomass and invertebrate density, and increasing taxa richness was related to increasing stability. Invertebrate community metrics of stream health (%EPT and QMCI) were degraded in pasture compared to pine and native forest, and community composition was influenced by both stability and water temperature. In these streams, establishment of mature pine plantations on pasture in soft rock terrain resulted in water quality and stream health conditions similar to native forest streams.