Precious soil being lost to the ocean – but should we focus more on fish than farmers?

Andy Loader, co-chairman of the Primary Land Users Group, has challenged information in an article, by Bala Tikkisetty, Sustainable agriculture co-ordinator for the Waikato Regional Council, published in the New Zealand Herald in mid-December.

The article (HERE) said more must be done to stop the slide of soil into waterways and, ultimately, the ocean.

“It makes economic sense to do so and also helps better protect our waterways and aquatic life from the effects of sedimentation.

“The scale of this loss of a farmer’s most precious resource is huge in this country.

“We lose it to the ocean about 10 times faster than the rest of the world, with between 200 million and 300 million tonnes sliding into the sea every year.”

New Zealand’s total land area is just less than 268,000 square kilometres. The top estimate implies we will lose the total land area of New Zealand to a depth of 1 metre over the next hundred years – roughly – from this soil erosion.

Mr Loader (see HERE) notes the article does not mention the effects of pest fishes on the scale of the erosion problem, particularly in the Waikato and Waipa River catchments.

According to Mr Loader’s estimates, there are approximately 500,000 tonnes of Koi Carp alone in this area. These produce about 14 times their own bodyweight of sediment per year (seven million tonnes), by their feeding method.

Where do the regional council figures come from, he asks, because “they seem excessive to me?”

The article by Bala Tikkisetty also states:

Waikato Regional Council staff can advise on best practice at individual sites. The council also has funding (up to 70 per cent of costs) available to help farmers in priority susceptible west coast and Waipa catchments to carry out erosion control and other land management activities.

Funding covers:

– tree planting, including pole planting and native plant species

– fencing off marginal land or bush from active use

– riparian management (fencing, planting and stock water reticulation)

– farm plans to identify soils, land use capability and environmental projects.

Mr Loader says it is great to see the council doing something practical to improve the water quality in the catchments, but

“… the fact of the matter is that the majority of the waterways around farms are already fenced and further fencing will not have a huge effect on improving water quality unlike other issues.”

He wants the council to provide funding to remove pest fishes from these catchments.

“Surely with the pest fishes creating so much sediment in the waterways as well as the other environmental damage that they do, their removal would achieve huge improvements very rapidly.”

Many people are unaware of the damage done to our waterways by pest fish, Mr Loader contends. But introduced fish have spread into the wild, become pests and are threatening New Zealand’s freshwater species and environments by:

• Stirring up sediment and making the water murky

• Increasing nutrient levels and algal concentrations

• Contributing to erosion

• Feeding on and removing aquatic plants

• Preying on invertebrates, native fish and their eggs

• Competing with native species

Mr Loader agrees with much of what the article says, but questions why it seems to single out farming as a main contributor to the effects of erosion when there are other causes such as natural water courses, urban development and vegetation removal outside of farming.


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