Land use impacts on water quality
Case Study 1
A 2-year water quality study of the Motueka River catchment at the start of the ICM research identified poor water quality in one area, due largely to the daily crossing of streams by dairy cows.
The resulting nationally recognised ‘Cows in Creeks, Cows out of Creeks’ study with NIWA, Cawthron, Tasman District Council and NZ Landcare Trust resulted in a more than 50% improvement in bacterial water quality in the Sherry River. This was achieved through collaborative research with landowners, and their consequent investments in bridging both dairy crossings and forestry crossings further upriver.
This work was followed by further water quality sampling in conjunction with Tasman District Council and landowners, resulting in the newly formed Sherry Catchment Group committing to further improve river water quality to swimmable standard through voluntary action.
Best management practices (BMPs) for the range of land-use types in the Sherry have been developed and a BMP library established on the ICM website.
Researchers also developed and calibrated a model that tracks faecal bacteria movement and die-off. In 2009/10, this was linked to the IDEAS model in which impacts of land-use change in the river and bay were assessed for six land-use scenarios (see integrated modelling).
Riparian management has been a focus of mitigation of land impacts on water. The current and potential riparian status for river reaches across the whole Motueka catchment was mapped along with scoring of the riparian functions to identify where riparian restoration should be prioritised.
A farmer-maintained riparian restoration trial with Scion has provided guidelines for farmer-friendly riparian restoration with native plants in weedy environments, aimed at providing stream shade and excluding stock from riverbanks.
Aligned with the Sherry riparian work is the database of the stabilising potential and growth characteristics of New Zealand’s indigenous plants developed from two field trials in Gisborne. Together with riparian condition mapping, riparian restoration trials with the Sherry River farmers, and assessment of river bank styles, this work is advancing riparian restoration method development nationwide.
Andrew Fenemore
Chris Phillips