Threats to Wetlands

Remaining wetlands face many pressures. Continued drainage directly affects wetlands, as does reclamation and land conversion. Indirect effects include runoff of nutrients, sediment and contaminants from adjoining farmland and urban areas and effluent discharges into wetlands. Livestock, plant and animal pests can also cause problems. Careful management can decrease the effects of these threats on our wetlands.

Drainage and other alterations to hydrology

Drainage and cultivation have greatly improved our ability to farm land profitably in the Canterbury Region. But it has also caused the loss of most of the Region’s wetlands. We must retain our remaining wetlands to protect their biodiversity and maintain the services that wetlands provide (for example, flood management and improving water quality).

It is not only drainage of wetlands or near wetlands that can affect their water levels. Changes further upstream, such as damming or channelling waterways and groundwater abstraction, can change how much and when water reaches a wetland. Coastal erosion in South Canterbury is threatening coastal wetlands in this part of the region.

For policy information on diverting and damming water, and abstraction of surface and ground water contact us to get in touch with a regional planner.

Poos! Poos in the water!

Stock

It is best to keep stock away from wetland areas as they can damage soils, disturb native plants and animals, and dirty the water. You can reduce damage to wetlands by only grazing pasture near them from mid-summer to mid-autumn.

Stock with uncontrolled access to wetland areas can:

• increase nutrient levels through their urine and dung
• compact or erode the soil
• disturb wildlife
• graze on and trample wetland plants
• open up sites for weed invasion
• carry weed seeds in their hooves, coat, or dung
• become bogged down and trapped.

Wetlands, and valuable stock, can be effectively protected from each other with standard fencing. However, controlled sheep grazing is not always detrimental. Some wetland reserves are currently deliberately grazed as part of their management, to help control exotic plant species.

Increasing nutrients

Fertiliser applied to farmland can affect nearby wetlands through nutrient enriched runoff, leaching and spray drift. Nutrients can also enter wetlands during storms or floods, when eroded soil washes down into wetlands.
Increased nutrients in wetlands, particularly low nutrient bogs, can change the delicate balance of plants and animals in the wetlands, aiding the invasion of exotic plants, such as grey willow.

Plant pests

Plant pests threaten native biodiversity in many lowland Canterbury wetlands. They can grow very quickly and compete against native plants for space, nutrients and light. Exotic willows now cover many of the remaining freshwater wetlands in the Region. Other plant pests, that are not yet widespread in Canterbury but have high potential for further spread, include the aquatic weeds egeria (Egeria densa), entire marshwort (Nymphoides geminata), oxygen weed (Lagorosiphon major), the tall grass phragmites (Phragmites australis), and yellow flag (Iris pseudacorus).

Purple loosestrife (Lythrum salicaria) is a serious weed of wetlands and waterway margins. Purple loosestrife has now become established in several locations in New Zealand, including Canterbury. Until relatively recently, purple loosestrife was available through garden centres and nurseries. However it has now been declared an 'unwanted organism' under the Biosecurity Act. This means that it can not be propagated or sold.

Environment Canterbury’s control regimes for plant and animal pests are detailed in its Regional Council rules for controlling plant pests.

Contact our pest plant staff about identifying and killing weeds.

Animal pests

Deer, rabbits, hares, and pigs have become established in some wetlands and pose a threat to native plants and animals. Rats, cats, possums, hedgehogs and mustelids are also found in Canterbury wetlands. They kill native birds especially during the breeding season when incubating birds are often reluctant to leave the nest. Young chicks and eggs are also taken, as are other native animals such as bats, lizards and insects.

Environment Canterbury, through the Regional Pest Management Strategy, carries out some wetland pest control.

Contact our animal pest staff about identifying pests and killing methods.

Fires

Fires were a natural occurrence in some wetlands and many native wetland plants are adapted to fire. Some have underground rhizomes (runners) that can rapidly sprout after a fire. Others rely on fire for their existence as they grow in burn holes (small clearings created when fire removes the vegetation in localised areas).

But wetlands now are much smaller than they used to be, and a single uncontrolled fire can burn most or all of a wetland. When a whole wetland is burnt, few plants and animals survive to re-colonise the burnt area. Animal survivors in particular will not live for long without the cover and food provided by nearby vegetation. Burnt wetlands are also more susceptible to invasion by introduced plants.