The effectiveness of riparian 'restoration' on water quality - A case study of lowland streams in Canterbury, New Zealand

Abstract

In New Zealand, around half of the lowland water bodies do not meet water quality standards, primarily due to widespread changes in land use. Riparian restoration has been occurring in New Zealand for over 30 years in an effort to minimize this impact, however, little monitoring of restoration effectiveness has been undertaken. This study evaluated the impact of riparian plantings on water quality of lowland streams in the Lake Ellesmere catchment. A paired-catchment design on four river reaches was used to compare restored riparian buffers with control sites upstream. Chemical water quality sampling was used in conjunction with a macroinvertebrate community assessment. Equivocal benefits of riparian restoration were observed, with improvements in some variables but not in others. Riparian restoration had a positive effect on water quality in terms of increasing dissolved oxygen and decreasing turbidity. However, conductivity increased at planted sites and no changes were observed in other variables. These findings may be affected by the insufficient width of all four buffers, and gaps in the buffer system contributing to poor water quality. Although variable responses were seen in invertebrate community composition, this research suggests that even narrow planted buffer strips may be effective in improving some water quality parameters. The overall mixed results present a fair assessment of the benefits of riparian restoration that may be expected within a relatively short time following vegetation establishment. Even when no baseline data have been established prior to restoration, this research showed monitoring can demonstrate the effectiveness of riparian restoration.