Lakes and rivers around Wellington are some of the most polluted, and the dairy boom will only make the problem worse, a new report says.
Nutrient runoff is a major cause of poor water quality, breeding invasive weeds, slime and potentially toxic algal blooms. Last summer toxic blooms in the Hutt and Ruamahanga rivers killed several dogs.
Parliamentary Commissioner for the Environment Jan Wright issued a report yesterday projecting global milk prices would continue to increase the popularity of dairying.
Modelling found almost 25,000 hectares of pasture for sheep and beef cattle would be converted to dairy farms in the Greater Wellington region by 2020.
Most of this would be in Wairarapa, though farmland on the Kapiti Coast would also be converted.
Dr Wright said studies showed more nutrients ran off land after it was converted to dairying than when used as pasture for sheep or beef cattle.
The nutrients of most concern 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 swimming spots.
Rivers such as the Mangaterere and Ruamahanga, which ran through farmland, and lakes Wairarapa and Oneke currently suffered from nutrient runoff.
Greater Wellington Regional Council chairwoman Fran Wilde said that while water quality was "not good", work was being done to remedy the situation.
A committee was being set up to develop a Wairarapa water management strategy over the next few years. "It's taken decades and decades to get to this state and it will take some time to improve it."
DairyNZ sustainability spokesman Rick Pridmore said irrigation projects in the Wairarapa could increase the number of dairy farms, but the projection of unconstrained growth was "unrealistic".
"We're working with Greater Wellington Regional Council to understand what needs to be put in place so that doesn't happen."
- © Fairfax NZ News
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