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Aslan Wright-Stow.
Riparian buffers and constructed wetlands reduce contaminant loss to waterbodies, but by how much?
DairyNZ water quality specialist Aslan Wright-Stow explains a national project aimed at finding out, and why this matters as regional limit setting ramps up.
Many landowners are in the process of identifying and implementing ways to reduce contaminant loss to waterbodies, which are increasingly required by regional limit-setting processes.
Constructed wetlands and riparian buffers are at the forefront of the options available, but we need to know how they perform in all landscape settings so we can optimise their performance, and as a farmer your efforts to reduce contaminants are rewarded in farm nutrient/ contaminant budgets.
The project is jointly funded by DairyNZ (through the farmer levy), the National Institute of Water and Atmospheric Research (NIWA) and regional councils. It’s taking place over five years, beginning by developing provisional performance and design guidelines for immediate use, based on current scientific understanding.
At the same time, we’ll design, establish and monitor a range of riparian buffer and constructed wetland systems across New Zealand to quantify and compare performance in different landscape and climate settings.
Wetlands and riparian buffers
Monitoring the constructed wetlands is a relatively straightforward exercise comparing the quality of water entering and exiting the wetland to determine contaminant loss1. The aim of the riparian monitoring is to find out if having wider buffers at locations where runoff is more strongly focused (‘critical source areas’) will improve flow and contaminant filtering. In principle it should; however, testing this at catchment scale has so far not been done here or overseas.
We’ll identify and compare suitable paired catchments throughout the country, each pair having a standard fixed-width buffer and a variable-width buffer (made wider at critical source areas and narrower where overland runoff is less important). We’ll be trying to find out how optimal water quality return relates to cost, time and farm productivity.
While mainly focused on reducing primary water quality contaminants (sediment, nitrogen, phosphorus and faecal microbes), this project will also provide new information on flow buffering, biodiversity and habitat enhancement. It’ll identify options for addressing issues related to climate change as well (e.g. providing stream shading, managing water temperatures).
The project’s results will enable us to guide farmers’ water quality initiatives so you can meet regional limits, improve water quality on your farm and get greater certainty of performance.
It will make your efforts more cost-effective, but also ensure your efforts are rewarded by authorities in nutrient budgets. Our results will also identify what works where and on what scale, so water quality efforts can be tailored to suit individual and regional situations. Overall, the research project will quantify the performance of riparian buffers and constructed wetlands to ensure farmers are recognised for their water quality efforts.
• This article was originally published in Inside Dairy May 2018
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