New wetlands considered to help Waituna

Cain was born in Lumsden and grew up on a small sheep farm at Rimu. He works with Southland's rural community as part of his day job and was recently a member of the Southland Regional Forum.

“As a Trust, we’ve looked at ways to prevent contaminants from flowing down into Waituna Lagoon. You can undertake measures on-farm such as using nutrients more efficiently or capturing contaminants before they leave the farm boundary.”

Wetlands are an important tool because they act as a filter, trapping sediment and improving water quality. They can also provide a buffer against erosion, prevent nutrients from leaching into waterways, reduce the impact of flooding and provide native habitats and recreational opportunities.

“With a trial to construct a wetland, we’ll learn about how much it costs to construct it, what are the best ways in these peaty soils to get water into the wetlands. You can have large wetlands where you take water off the creek, go through the wetlands and come back out; or you can have wetlands where the water soaks in like groundwater.”

Investigations into the site location and scale of constructed wetlands are now underway, with potential for at least one wetland to be created on land purchased recently.

Whakamana te Waituna Trust co-chair and Environment Southland chairman Nicol Horrell says land bought for the Whakamana te Waituna project is a valuable addition to work underway to clean up the Waituna Lagoon.

“Some 150 hectares of land in two large parcels, plus a few smaller strips, has been strategically purchased because the land is flood-prone, and has been difficult for previous owners.

“Being able to use the land in this way means we’ll be able to learn more about the tools available to us to reduce contaminants reaching waterways, and this will hopefully be useful for other parts of our region.”

Cain says the Trust engaged consultants to look at potential wetland options based on the previous research undertaken in the Waituna catchment and throughout New Zealand.

“There are two scenarios to test and understand – building a whole lot of small structures, or building a larger scale, catchment wetland.

“The disadvantage of building numerous small structures across the catchment is the maintenance – if you’ve got 200 little structures you’re trying to manage as a project, it’s very difficult and quite costly to get around and maintain all those and make sure they’re working. For this type of project, it’s clear it will be more efficient to have a small number of larger-scale interventions.”

Five separate wetland sites were identified and the feasibility of the best sites will be decided in the next few months.

“We still have a way to go before the decision is made to proceed, but hopefully that can happen by early next year. If this trial is successful, the next stage would be to look at a large-scale 100-hectare-plus constructed wetland on the western side of the catchment where Waituna Creek flows down.”