NIWA’s Dr. Chris Tanner hosted an insightful session at the Primary Industries Summit earlier this month covering how wetlands were viewed historically, how they are viewed today and the science behind how they help support sustainable farming ecosystems.
Wetlands exist where the land is either permanently or tidally covered by shallow water, and where that water is the main element influencing the existence of plants and animals within it. They generally begin with a sedimentation pond followed by a shallow downstream area populated with dense vegetation rooted just below the water’s surface.
To borrow Chris’ metaphor wetlands are the ‘kidneys’ of the land, with dense vegetation acting as a filter to mitigate nitrogen waste leakage (up to a 40% reduction in ideal conditions) into waterways while simultaneously increasing the ability of downstream land to cope with flooding by restraining water flow rates. Wetlands also enhance the biodiversity of surrounding areas by supporting wildlife, and most importantly they do all these things at no cost.
Historically farmers viewed wetlands as a waste of space, draining and converting them into pastures on a massive scale. Of course, that all happened before the role they play in surrounding ecosystems was fully understood and as a result much that would have been useful for today’s farmers has been lost: Only ten percent of New Zealand’s pre-colonial natural wetland areas remain.
Many modern farms utilise riparian zones as a buffer between farmland and connected waterways, and essentially this is what wetlands do over larger areas with much larger volumes of water.
For farmers looking to create an on-farm system that is resilient to flooding, wetlands can be an effective low-maintenance element of a wider management plan that yields positive side-effects as a bonus. Given these benefits, Chris did concede that wetlands do take up a considerable amount of space. However, since they can often be sited on non-productive land it’s uncommon for them to have a noticeable effect on farm productivity.
Aside from educating about the role of wetlands, another of NIWA’s focuses is building back some of what was lost. While they have had success and currently monitor six large wetlands under construction, to date only a small percentage of their original land mass has been restored. NIWA has published guidelines for land owners wishing to construct wetlands on their properties, Click here to view.