What value a stream’s ecology?
Development affecting an Auckland stream. (Photo: Stephen Moore, Landcare Research)
Several kilometres of stream habitat are lost each year to development in the Auckland region. Developers are often asked to fund the improvement of stream habitats at a different site, thus offsetting the ecological damage they have caused. But different reaches of a stream, or streams in different locations, have different ecological values, so ARC asked an interdisciplinary team, including NIWA, to establish an ecological basis for setting mitigation ratios – that is, the units of stream restoration needed to balance the units of stream degradation.
The team came up a novel system v Stream Ecological Valuation or SEV – for calculating a relative ecological price tag. The method is based on the functions that streams provide, such as natural flow regimes, connectivity for species migrations, de-contamination of pollutants, and provision of aquatic habitats, amongst others.
‘A really useful part of the SEV process is that it not only gives you an idea of the functions that might be lost by development affecting a stream, but it also allows you to predict improvements in stream function if you are restoring a stream,’ says NIWA scientist Steph Parkyn.
ARC is very pleased with the results of early trials and has adopted SEV as its preferred method for stream environmental impacts assessments. A NIWA-led team aim to expose the method to international peer review this year, and will adapt the SEV for other regions around the country in the future.