Thursday, March 28, 2024

Regimes under scrutiny

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Before and after measurements of water quality and biodiversity for a dairy farm conversion are throwing up a mix of early results on Limestone Downs, the big northern Waikato trust-owned property.
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Researcher Gerry Kessels, of Kessels Ecology, Hamilton, told the annual Limestone Downs field day his staff members were two years into a three-year study started in May 2013.

Some 400ha of the coastal flats were converted to dairying during winter 2013 and the 800-cow herd began milking in early August.

The dairy unit is only 20% of the large coastal property and is 25km from its nearest dairying neighbour.

The Kaawa Stream runs through the dairy unit on its relatively short journey from the hills to the Tasman Sea, about 15km down the coast as the gull flies south of Port Waikato.

Limestone Downs also contains another coastal stream, the Waikawau, which runs through the sheep and beef paddocks after rising in native bush.

Kessels staff are sampling and surveying that stream too.

It was the lack of water quality measurements in those streams that caused a delay to the resource consents process for the dairy conversion.

Surveys of fish and macroinvertebrates are done with nets, Kessels said.

Macroinvetebrates are mayflies, caddis flies, stoneflies and other insects that are very sensitive to water quality and are therefore good indicators of stream health.

The Kaawa has inanga (whitebait as juveniles), gambusia, the common bully, grey mullet, eels and koura.

Inanga eggs were also found in the Kaawa downstream sampling site, deposited in dense clumps of paspalum grass that had been fenced to prevent stock access. An adjacent unfenced bank contained no inanga eggs.

The macroinvertebrate levels were quite low because they need riparian covers to complete their life cycles.

In general, conditions at three sampling sites on the Kaawa were similar – soft substrates, abundant aquatic plants and high water clarity when flows were low.

Water sampling from the Kaawa and the Waikawau showed quality was seasonally variable.

The Kaawa downstream site (in the tidal zone below the dairy parlour) has showed the highest ammonia and total nitrogen levels, most likely from nitrogen applied to pasture.

However, it was well below the acute toxicity levels for fish and “tracking well for long-term or chronic toxicity”, Kessels said.

The E-coli levels in the Kaawa were below threshold but peaking higher in the Waikawau, most likely because of livestock access and the possibility of feral pigs and goats in the bush headwaters.

Dissolved phosphate levels were also tracking upwards in the Kaawa and the Waikawau, he said.

Limestone Downs and local iwi Ngati Tahinga have a memorandum of understanding on the objectives for the management of water quality.

Kessels Ecology is drawing up a planting plan for the riparian zones and selected wetlands in consultation with Ngati Tahinga.

The project results will provide pre-and post-conversion comparisons and ultimately comparison of the scientific findings with cultural indicator references.

“The Limestone Downs work is one to two years ahead of the Fonterra-DOC Living Waters programme in the Waikato peat lakes,” Kessels said.

“We aim to provide a case study for the scientific and farming communities detailing the effects of dairy farm conversion on key aquatic biodiversity and cultural indicators.

“As well we will evaluate the efficacy of initial farm and livestock management regimes and stream retirement and planting programmes for enhancing stream biodiversity.”

This information could then be used to inform recommendations for monitoring, management and restoration options on Limestone Downs and other dairy farms.

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