How to plan a wetland restoration
Nathan says thinking, researching, and planning need to come before you start digging anything. You don't have to do everything at once. Nathan suggests designing and implementing your project in stages.
It's important to ask yourself:
• what do you want to achieve?
• what is there now that could be included in your plan?
• what do you want to improve? Nathan says the two most common motivations for landowners he works with are improved biodiversity and water quality.
Chapter 2 of Landcare’s Wetland Restoration Guide (see page 33 for how to get a free copy) has excellent advice. It recommends sketching a rough concept plan, showing:
• a bird's eye view diagram of the area, to scale, as it exists now;
• the same view, as you'd like it to look once developed.
Google Earth can help as a basis for mapping. Ask your regional council if it has detailed contour information on your block as it helps when working out level changes and mapping zones. Zones are organised around different water levels and the plant types that thrive in them.
It's important to find out how water gets into your wetland:
• has the water table surfaced?
• is it fed by groundwater or runoff, or both?
Think about your land’s place in the water catchment
The catchment influences the amount and regularity of water inflow and what it carries in the way of sediment, nutrients, and possible pollutants. A lifestyle block is unlikely to contain an entire catchment. It will be affected by high nutrient or sediment run-off from larger or more intensely-farmed properties on the land above you.
Ideally, get neighbours to work with you for the benefit of the whole catchment. Catchment groups are strongly encouraged by the NZ Landcare Trust, councils, and industry bodies. Seed funding may be available.
Cleaning up the water
If sediment-heavy water flows into your wetland, the key to cleaning it up is to slow it down. The slower it goes, the more sediment drops out.
The best strategy is a sediment trap above a dam or wetland system, says Nathan. Without a sediment trap, the wetland will quickly fill with silt.
You'll need to dig a trap out periodically; the silt will be rich in phosphorus and may be a useful soil amendment on other areas of your block.
There are also native and exotic species that do a great job of sucking up nitrogen from nutrient-heavy run-off. Consult local plant advisers about what works best in your area. It's possible hemp may be a good option for this purpose in the future, but growing it is still heavily regulated.
How to bring in the birds and other wildlife
Waterfowl such as bittern, rails, spoonbills, and Muscovy ducks prefer shallow water, less than half a metre deep. If you're excavating soil to increase water retention, create wave-shaped edges and gentle slopes, so it's easy to walk down into the water. Give your digging contractor specific instructions or most will create a typical farm dam which has steep sides and straight edges.
The margins around the water are essential waterfowl habitat. To create good habitat:
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plant densely at the water's edge to provide nesting areas;
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don't tidy up dead wood as it provides insect habitat and organic matter. More insects mean more food for birds and greater biodiversity;
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create roosts by jamming large rocks or dead logs upright in the water – it's best to get that done when you have the digger on site;
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rats and mustelids are strong swimmers, so artificial islands and snags won't be predator-proof – talk to your council, DOC or nearby landowners to get advice about what pests are in your area and what methods work best to control them. Effective pest control takes multiple, longterm approaches.
The Parsons’ block, showing their wetland’s proximity to the Opawa River. Despite a lot of planting, the couple has battled with persistent weeds such as crack willow, oak, and Tasmanian ngaio. The water can be drained and then refilled from an artesian bore, which Will did one year to eradicate an oxygen weed infestation.
Will and Rose Parsons bought their block near Blenheim partly because of its beautiful 8ha wetland. It covers most of their block and drains into the nearby Opawa River.
The wetland was established by the previous owner, a keen duck hunter who mixed native plantings with exotics, including fruit and nut trees. The Parsons have chosen to remove the exotics and plant more natives. The reforestation offsets the carbon emitted by their business, Driftwood Eco-Tours.
A QEII covenant means the wetland is protected, even under future owners.
The Parsons' say the appearance of rare native fernbirds has been a thrilling reward. The area is now a mature eco-system, which Will describes as “self-managing”.
Who: Will & Rose Parsons Land: 12.8ha Where: Riverlands, 8km east of Blenheim
Sedges and rushes are closely related. Sedges are perennials; rushes may be annual or perennial. Sedge stems are typically triangular, unlike rushes. But both have solid stems, compared to the hollow stems of grass. There are more than 2000 species of sedge; Carex is a common plant family in New Zealand wetlands.
The deciduous exotics in Ian Moore's wetland are bright enough to light up a grey day in late autumn.
Many landowners and community groups are strongly committed to reforesting wetlands and other areas only with natives grown from seed collected in the same region.
Another point of view values the eco-system functions of exotic trees. Ian's wetlands include liquidamber, tupelo (Nyssa sylvatica), and pin oaks (Quercus palustris). The tiny acorns of pin oak are a perfect size for ducks and provide a nutritious protein boost for waterfowl.
The swamp on the edge of Lake Rotokare, 50km south of New Plymouth, reaches right up to a dense forest. The community-led project is headed by a charitable trust which cares for a 230ha reserve, protected by a predator-proof fence. It features in DOC's publication, Magical places – 40 wetlands to visit in New Zealand (available here: bit.ly/magicwetlands).