By Murray Neilson, a retired technical support officer for freshwater ecosystems with the Department of Conservation in Otago, a trustee of the Clutha Fisheries Trust and a former Fish and Game counsellor in Otago.
I regularly read Alan Emerson’s column, as I feel a kind of kinship with him, hailing as he does from the Wairarapa, my old home district (I’ve been an Otago resident since 1975) and I find I often agree with his opinions. However, in a recent column, “I do wish they’d dry up about wetlands”, he wrote disparagingly of wetlands and their place on farms along with recent legislative changes designed to protect them. This had me wondering.
Alan asked: Where would we be “if we hadn’t drained the swamps”? It’s true that wetland drainage brought a tremendous amount of rich, valuable flatland into agricultural production. We were so good at it that we drained and developed approximately 90% of our original wetlands. That’s also the very reason we should be protecting what little we have left and restoring those that we can.
So, let’s go back to basics – what is a wetland? According to the Department of Conservation website, wetlands are defined as areas where water is the primary factor controlling the environment and associated plant and animal life. They can be freshwater or estuarine (located at the coast with brackish water). Apologies to those of you for whom this is “old hat”.
Also: “Wetland is a generic term for the wet margins of lakes, ponds, rivers, streams, estuaries, lagoons, bogs and swamps,” according to the Waikato Regional Council in 2020.
The Resource Management Act of 1991 defines wetlands as including “permanently or intermittently wet areas, shallow water, and land water margins that support a natural ecosystem of plants and animals that are adapted to wet conditions”, as Alan noted in his column.
So, now we know what they are, let’s examine some of the values and benefits of wetlands. These systems are considered valuable because they clean the water, recharge water supplies, reduce flood risks, and provide fish and wildlife habitat.
In addition, wetlands provide recreational opportunities, aesthetic benefits, sites for research and education, and commercial fishery benefits, according to the DoC website.
“Natural wetlands have been appropriately termed the ‘kidneys of the landscape’, because of their ability to store, assimilate and transform contaminants lost from the land before they reach waterways,” according to the Walkato Regional Council in 2020.
So it seems they definitely have some values and benefits worth looking after. But before you dismiss this article as merely the ravings of another misguided “greenie”, consider the following from the DairyNZ website:
“New Zealand has lost 90% of its wetland areas due to drainage, land development and land use change. Protecting, restoring and creating wetlands on farm can reduce nutrient and contaminant loss, decrease the impact of floods and provide valuable habitat for native plants and animals.”
Here we have the conservation sector, a regulator and the organisation representing our most intensive farming sector all agreeing that wetlands on farms have values and benefits worth protecting – quite remarkable, wouldn’t you say, given the somewhat fraught history of past relationships between and amongst these organisations.? Must be something to it, right?
Some years ago AgResearch carried out a study in the Pomahaka catchment in west Otago, examining the relationship between retention of small on-farm wetlands and downstream water quality. It found that there was significant retention of run-off containing nitrogen, phosphorus and sediment within these wetlands (wet seeps, boggy gullies and depressions) on those properties which had retained them, versus those properties which had drained them, where these pollutants ran straight off into the nearest stream during wet conditions.
In other studies by AgResearch, protection and fencing-off of such wetlands was found likely to result in reductions of 50% of nitrogen, 10% of phosphorus and 60% of sediment, in overland flow entering the wetland.
For facilitated or constructed wetlands, the reductions were likely to be in the range of 30-60% of nitrogen, 50-80% of particulate phosphorus and 60-80% of sediment, in annual load in surface run-off entering the wetland. Significant reductions, I think you would agree?
The DairyNZ website also contains a YouTube video from Waikato dairy farmer John Hayward, who has created and fenced off a series of small wetlands in a wet gully system on his property. He has found that he no longer has any problems with cattle getting stuck in wet areas, the nutrients produced on farm are retained on farm, tuis and wood pigeons are visiting the plantings he’s put in and pheasants are nesting in the grass cover inside the fences.
He has received subsidies from Waikato Regional Council to assist with this project and he estimates that the costs are in the order of $5-$7/m for fencing and $3/planting. He sprays for weeds, such as blackberry, every two years, but says they’re not too much of a problem.
So, the next time you’re considering sticking a digger up that wet gully to clean it out or to drain that seep to tidy up the farm, think again. Weigh the cost of doing that against the cost of a bit of fencing to protect and retain it.
Downstream water quality will benefit and, if you’re a gamebird hunter, that nesting pheasant or mallard duck (ducks need long, rank grass for nesting cover, as well) may well produce the brood that will provide you with hunting opportunities in years to come.
While you’re about it, plant a few flax plants too. In a couple of years when they bloom you’ll have tuis and bellbirds visiting to feed on the nectar they’ll produce – all adding to the beauty and biodiversity of your property.
Check with your local regional council to see if there is any assistance available to help you with this.
Oh, and Alan – you watch that YouTube video [below]!
