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Published: 2004-11-30 00:00:00

Converting forest to pasture within the Waikato Catchment would increase nutrient loads in the area’s waterways and groundwater, as well as affecting flood levels, soil contamination, greenhouse gases, biodiversity and the landscape, this week’s Environment Waikato Policy and Strategy Committee meeting heard.

Special Projects Manager Dennis Crequer told the meeting that converting established plantation forest to pasture, mainly dairying, had become relatively common and the rate and scale of the change was likely to increase markedly in the future.

Over the past few years Carter Holt Harvey had already sold about 5000 ha of the Kinleith estate near Tokoroa and most was converted to dairy pasture.

Almost all of the land sold so far was within the Waikato Catchment. Although significant areas of the Mamaku Plateau – a major source of high quality groundwater – was included in the CHH Kinleith forest, it was not known at this stage whether or not significant areas of that land would be sold and converted to pasture.

The single largest block of land identified for conversion in the Region however was the Waikato Tauhara Lease Lands near Taupo, now owned by Wairakei Pastoral Ltd. Previously owned by Tenon, this forest had been sold to a group of private investors, with Landcorp contracted to undertake the conversion on behalf of the company. The 25, 693 ha would be used for dairying, beef and sheep and cropping and take 15 to 20 years to complete.

Even if all of the land use changes were to a very high standard, including protection of watercourses, conversion would result in a significant loss of nutrients which would reduce water quality in groundwater and tributary streams, the Waikato River and the hydro lakes.

Using just the WPL block as an example, Environment Waikato staff had estimated nitrogen loss to ground and surface water could increase by up to 426 tonnes a year, and phosphate by 34 tonnes a year, compared with an estimated loss of 34 tonnes of nitrogen and two tonnes of phosphate under the present forestry use. This would significantly increase nitrogen in the Waikato River.

As well, the anticipated land use changes were likely to result in increased discharge of pathogens from stock, increased sediment loss from pasture and cultivated areas, increased fertiliser, herbicide, pesticide and animal remedy use as well as possible loss of aesthetic and in-stream ecological values, affecting other water users.

Greater overall volumes of water would reach rivers, floods would peak in shorter time and peak flows would be higher, with possible reductions in tributary flows and increased demand for irrigation. Other issues included landscape change, carbon issues, effects on biodiversity, transport and soil erosion.

The partnership between Environment Waikato, Taupo District Council, Tuwharetoa and Central Government and landowners in the Lake Taupo catchment would remove about 100 tonnes of nitrogen a year from Lake Taupo costing $83 million in new funding added to $62 million already invested in lake protection.

Chairman Jenni Vernon said the Council needed to address non-point discharges just as it had tackled point-source discharges in the past.

“Farmers who use the natural environment are learning that their activities are having off-site effects. This is being acknowledged and even best practices at an individual level leave us with a cumulative impact to deal with in our catchment waterways.”

The Committee recommended directing staff to investigate how the Council could respond to the issues arising from land use changes in the catchment, reporting to the Committee’s February meeting.

This media item was current at its release date. The facts or figures it contains may have changed since its original publication.