Wetlands – the river’s kidneys

Researcher Cheri van Schravendijk-Goodman says that the wet, boggy places you see along the Waikato River as you drive north of Huntly towards the Bombay Hills may look like barren landscapes covered in swampy grasses, mosquitoes and cabbage trees, but they play a critical role in cleansing the water of the river.

Wetlands like kidneys

Cheri explains that wetlands are like our kidneys in our bodies. Our kidneys filter and cleanse our blood to remove wastes. Wetlands cleanse and filter out the pollutants in the water that comes from the catchment area before the water goes into the river.

Cleansing the water

Water flows slowly through a wetland, allowing sediment particles to settle out. Plant surfaces provide for filtration, the absorption of solids and add oxygen to the water. Wetland plants take up nutrients for growth – preventing them from entering the river where they may cause excessive aqua plant growth and upset the ecological balance of the river. Water entering the river cleansed by wetlands in turn protects downstream environments. All of this activity contributes to the health and wellbeing of the Waikato River.

Damaged wetlands of the Waikato

Wetlands are cradles of biodiversity, providing habitat for countless species of plants and animals. Pre-1840, wetlands covered about 17% of the total land area in the Waikato region. Urbanisation, industrialisation and the demand for agricultural production have now claimed much of the wetland area, leaving only 20–25% of the original wetland area.

These wetlands are in a poor condition. They are surrounded by agricultural land (receiving influxes of high levels of nutrients from run-off) and filled with invasive pest plants and animals, which compete for the same resources as our native species. This affects the habitat of important kai species such as tuna (eels) and whitebait. The wetlands also have roads running through them – disconnecting species from food and habitats.

Restoring Whangamarino – the scholarship programme

Cheri is heading up a scholarship research programme where tribal (iwi) students studying at Waikato Institute of Technology (Wintec) are given the opportunity to work with scientists from Landcare Research and NIWA in Whangamarino Wetlands under a government-funded wetland restoration programme. Whangamarino is one of the largest wetlands in the Waikato region and is of Ramsar status.

The research programme is committed to wetland restoration. Students are given training in aspects of wetland monitoring such as geographic positioning systems, setting up plots and transects, insect identification and setting up traps for sampling of invertebrates. They then investigate areas of concern identified by scientists.

Nutrient enrichment

The effect of dairy farming intensification on Waikato wetlands is an area of concern. Under scientists’ guidance, Joshua Ormsby and Jonathan Brown investigated the effects of the nutrients nitrogen and phosphorus on the root growth of plants in different types of wetland – peat bog, fens and swamps. They found that increased nutrients don’t seem to affect swamps and fens, but the addition of phosphorus does appear to inhibit root growth in peat bogs. Phosphorus contained in fertiliser spray drift may threaten peat formation (roots are a major component of peat). A lack of peat will lead to a degradation of the unique peat bog ecosystem.

Plant and animal pests

Other investigations involve pest trees such as the grey willow. Willow colonisation is expanding, and these trees compete for resources with the native plants. Students have assisted wetland scientists to investigate the effects of chemical sprays for willow control while allowing the growth of native plants.

Scholarship student Rimutere Wharakura is investigating predator control in Whangamarino. Cheri says people don’t appreciate how much damage stoats and feral cats can do in the wetland – they feed off ground-nesting birds like the spotless crake and fernbird.

Preserving taonga

Cheri stresses this work is critical. “If we lose our wetlands, it will impact on the people themselves. Our tūpuna have utilised and lived amongst these systems for generations. The plants and animals that reside in our wetlands are taonga, but so too is the knowledge that we have about our relationship with them.”