Saturday, 17 March 2018 08:55

Wetlands the unsung heroes

Written by  Aslan Wright-Stow, DairyNZ water quality scientist
Wetlands help reduce contaminants reaching waterways. Wetlands help reduce contaminants reaching waterways.

A recent review commissioned by DairyNZ may surprise you at the effectiveness of wetlands in preventing contaminants from reaching waterways. 

Wetlands are often referred to as the kidneys of the land: they filter, absorb and transform water contaminants, so helping to reduce excess  reaching waterways.  

In particular, wetlands can very efficiently remove excess nitrogen by creating environments whose chemistry and hydrology are ideal for treating, in particular, shallow sub-surface flow, and runoff from dairy farms.

A recent review of scientific studies in New Zealand, by NIWA for DairyNZ, found seepage wetlands can reduce the amount of nitrate – a problematic form of nitrogen entering them by up to 75-98%; that’s higher than we previously thought.

We already knew protecting and enhancing onfarm wetlands reduces contaminants reaching waterways, but this review has highlighted how effective they can be.

Wetlands are also great at trapping sediment and sediment-bound phosphorus, reducing faecal bacteria and providing a habitat that improves biodiversity, while also mitigating flooding risk.

Wetlands are areas of land where the soil is permanently or temporarily covered by water saturating the soil. These are the areas where ponding quickly occurs and remains after rainfall, where springs emerge and where soils pug easily.

Seepage wetlands are commonly located where surface and sub-surface flow converge, often where a change of slope occurs in the landform.

The main process of treating nitrogen entering a wetland is called ‘denitrification’; it involves bacteria converting nitrate into harmless nitrogen gas before it can reach a waterway.

Wetlands work by creating the right environment for these bacteria to thrive. Nitrate  removal is maximised during increased soil-water contact periods, water travelling deeper into the soil where oxygen is absent, and plentiful sources of carbon from decaying leaves and sticks. Some nitrate removal also occurs via uptake by microbes and plants.

Farmers can act to improve wetlands’ function and, therefore, their ability to reduce the amounts of nitrogen reaching waterways. These steps include restricting stock access to prevent pugging and soil compaction, promoting the right sort of vegetation cover, reducing preferential surface flow paths and minimising surrounding earthworks.

To make wetland protection and enhancement easy, DairyNZ has partnered with regional councils and Landcare Research to develop regional planting guides and the national Riparian Planner -- free to use at riparian-planner.dairynz.co.nz. 

The tool helps you map farm waterways and wetlands, and assists with plant selection, budgeting and the recording of actions needed to meet Water Accord and regulatory requirements.

• First published in the February issue of DairyNZ’s Inside Dairy.

Featured

Australia develops first local mRNA FMD vaccine

Foot and Mouth Disease outbreaks could have a detrimental impact on any country's rural sector, as seen in the United Kingdom's 2000 outbreak that saw the compulsory slaughter of over six million animals.

NZ household food waste falls again

Kiwis are wasting less of their food than they were two years ago, and this has been enough to push New Zealand’s total household food waste bill lower, the 2025 Rabobank KiwiHarvest Food Waste survey has found.

Editorial: No joking matter

OPINION: Sir Lockwood Smith has clearly and succinctly defined what academic freedom is all about, the boundaries around it and the responsibility that goes with this privilege.

DairyNZ plantain trials cut nitrate leaching by 26%

DairyNZ says its plantain programme continues to deliver promising results, with new data confirming that modest levels of plantain in pastures reduce nitrogen leaching, offering farmers a practical, science-backed tool to meet environmental goals.

National

Machinery & Products

JDLink Boost for NZ farms

Connectivity is widely recognised as one of the biggest challenges facing farmers, but it is now being overcome through the…

New generation Defender HD11

The all-new 2026 Can-Am Defender HD11 looks likely to raise the bar in the highly competitive side-by-side category.

» Latest Print Issues Online

Milking It

Full cabinet

OPINION: Legislation being drafted to bring back the controversial trade of live animal exports by sea is getting stuck in the…

» Connect with Dairy News

» eNewsletter

Subscribe to our weekly newsletter