Tuesday, March 19, 2024

Riparian survey to capture data

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As the go-to option for managing sediment runoff, there are surprisingly few case studies showing how different approaches to riparian plantings work. Now Niwa researchers hope to change that. Richard Rennie spoke to freshwater ecologist Richard Storey who is leading the initiative.
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Farmers are being invited to provide information on their riparian plantings to help measure their effectiveness and provide a pool of data for future plantings.

“Riparian plantings are now a major investment people all over the country are working on and that includes dairy processors and industry groups,” Niwa scientist Dr Richard Storey says.

“But information is patchy on just how much is going on and if it is always having the effect they want it to.”

Fonterra suppliers alone had fenced 24,000km of waterways while the DairyNZ Water Accord reported cattle were now excluded from 97.2% of waterways on dairy farms.

Niwa had set up an online survey site, https://riparian.niwa.co.nz, and was inviting farmers and landowners to enter details of their riparian projects, including photos and species details.

Perhaps surprisingly, what data Niwa already had on riparian strips and stream health had delivered something of a mixed bag of data on their success.

“The water quality improvements are there in most of them,” Storey said.

“However, when it comes to whether insect and fish life comes back, that is less predictable.

“In some cases you may well find the invertebrate species like mayflies, that are a good indicator of stream health, just are not there despite the plantings.”

While far from being watery deserts, the water systems bore a resemblance to where they needed to be but could fall short.

The options for repopulation might include relocation of freshwater species into the stream within the planted or fenced riparian area. Another might be to encourage corridors of protected vegetation and waterways that allowed the species to spread naturally.

The second phase of the project intended to help with that understanding.

It would let farmers become “citizen scientists” with researchers making a selection of farmers from the survey responses who could be trained, equipped and supported as volunteers to monitor the water quality and stream life in their protected water courses.

Storey acknowledged riparian strips were by no means a silver bullet solution for the farming sector.

“There has been a lot in media on how successful they are.

“They don’t necessarily stop nitrate getting into streams if the groundwater flow bypasses the root zone of the riparian vegetation and pops up into the stream from deep springs but there are a number of other benefits they do offer for water quality and biology.

“They can indirectly help reduce nitrate’s impact by tree plantings shading water courses, in turn reducing the amount of algal growth that would otherwise develop due to nitrate levels in the water.”

Once determined, the area of riparian plantings could also provide farmers with a useful indicator of their ability to deal with another environmental issue circling farm businesses, climate change.

“While they tend to be too narrow to be recognised as carbon-offsetting forests under current ETS rules, the riparian strips at least give farmers some sense they have helped offset their own emissions by planting them.”

Niwa scientists were also working to determine the economic contribution riparian zones could offer through plantings such as manuka for honey production

“We are looking at a number of different products to grow there, including iwis’ medicinal plants and flaxes.”

The second phase of the project would give farmers tools for watercourse sampling.

Niwa has a Stream Health Monitoring and Assessment Kit and was considering the addition of real-time water sensors for web-based updates on watercourse health.

Despite some gaps in information to date, researchers do have some ideas on what constitutes a successful riparian area.

“The longer the strip is the greater its success will be because it takes a while for the temperature to drop and nutrients to be absorbed. The most successful ones are at least several hundred metres long.”

Generally, they should be 10m wide with dense plantings in part to reduce weed infestation and with thick grasses on the farm edge to act as a “mop” for initial runoff.

But ideal width for water quality benefit varied depending on factors including the adjacent land’s slope, length and soil drainage.

Storey said more information would also help determine how long restoration took to occur.

“Relatively quick responses are possible from pathogenic bugs and fine sediment reductions that occur with riparian strips.

“You can see a change within a few short years.”

But there can also be surprises due to legacy effects of stream channel narrowing in pasture.

He urged farmers not to despair over the time it might take systems to repair and improve.

“We are confident riparian planting is an effective long-term approach to improving waterway health.”

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