Waterways will get worse - Commissioner

Already choked with weeds and algae, waterways will get even worse as the dairy industry continues to boom, the Environment Commissioner says.

Poor-water quality is caused by the run-off of nutrients from farm land, which breeds invasive weeds, slime and potentially toxic algal blooms. Last summer toxic blooms in the Hutt River killed several dogs.

A new report projecting what the country's land use will be in 2020 said the environmental problems were only going to get worse, particularly in the lower South Island and Wellington.

The research, a collaboration between the National Institute for Water and Atmospheric Research and Motu Economic and Public Policy Research, found the popularity of dairying would increase with rising global milk prices.

In 2020, almost 400,000 hectares of beef or sheep farming land would be converted into dairy farms, according to the country-wide modelling.

Parliamentary Commissioner for the Environment Jan Wright said studies showed more nutrients ran off land after it converted to dairying than when used as pasture for sheep or beef cattle.

"Generally, stocking rates are higher on dairy farms these days and they've been getting higher and higher," she said.

The two concerning nutrients were nitrogen, typically from cows' urine, and phosphorus in the soil. When both washed into fresh water, there was an increased risk of unchecked plant growth clogging lakes and rivers, interfering with the food chain of fish and birds, and forcing the closure of popular swimming spots.

"Rivers that are warm and flow slowly and wind around are more vulnerable [as are] lakes that are shallow and warm," Wright said.

The modelling predicted that by 2020 there would be a large increase in nitrogen run-off in Canterbury, Otago, Southland and Wellington. They were all areas where farmers were frequently switching to dairy farming. Gisborne however would have decreased run-off.

Wright said she hoped the report would inform national and local government water quality policies and improve the practices of individual farms.

IrrigationNZ CEO Andrew Curtis said the report failed to take into account recent innovations in land-use management.

"We've already seen the introduction of farm-specific environment plans," he said.

"By identifying the environmental risks on farm and requiring actions to manage these, the plans hold farmers accountable."

DairyNZ environment policy manager Mike Scarsbrook said the modelling also missed factors such as regulated water nutrient limits in some areas.

"The uncontrolled growth of dairy farms put out in the report isn't likely to play out as it's been painted," he said.

Scarsbrook said nutrient limits set by the community, such as those on the Manawatu River, were a great tool for managing water quality.

New Zealand Freshwater Sciences Society president David Hamilton said the report stressed the dangers the business-as-usual approach could have on waterways.

"Best agricultural practice has to become the norm," the University of Waikato professor said.

"We also need to have a long-term vision about what sort of land use is appropriate according to the sensitivity of the receiving waters."

Forest and Bird advocate Kevin Hackwell said the projections indicated swimming and fishing in many of the country's lakes and rivers could become a thing of the past.

"The Government needs to accept that spending $400 million on building irrigation schemes like the one planned for Ruataniwha [in Hawke's Bay] is only going to make things worse," he said.

Resource consent should be required to start dairying, where nearby waterways were close to or beyond acceptable pollution limits, he said.

Fairfax Media