Simplicity effective: water quality results

Visitors to a Waikoikoi water quality trial site last week inspect a sediment trap successfully...
Visitors to a Waikoikoi water quality trial site last week inspect a sediment trap successfully reducing turbidity and phosphate in the Pomahaka catchment. PHOTO: LLOYD MCCALL/SUPPLIED
"Citizen science" is helping a group of West Otago farmers make dramatic strides in environmental water quality.

The Pomahaka Water Care Group released its latest water quality results to stakeholders last week, results which demonstrated simple steps could have dramatic effects, spokesman Lloyd McCall said.

Nearly four years after the award-winning group was established with the aim of improving water quality for future generations to enjoy, work led by NZ Landcare Trust continued on multiple fronts.

Last week's annual meeting was combined with a series of wetland trial site visits across the catchment, which allowed members and other interested parties to see what was working, and what improvements could be made.

All trials were conducted by farmer members, Mr McCall said, making it a case of "citizen science".

"There are two trial wetlands and sediment traps completed with ORC collecting water quality information on their effectiveness. Another two sites have just completed development.

"The initial tests are very encouraging."

At Bill and Pam McCall's farm in Waikoikoi, a tile drain had been opened about 50m from its entry to an external drain.

Here had been placed a small sediment trap, followed by a 50m wetland area planted in sedges, rushes and other riparian plants.

Sediment traps aim to reduce turbidity (muddiness) and phosphate (carried by sediment) leaving tributaries; riparian planting has been shown to reduce nitrates, ammonia and E. coli.

"In the latest results, E. coli is showing massive reductions - in excess of 90% at times," Mr McCall said.

"Ammonia is also being drastically reduced resulting in a significant reduction in total nitrogen entering the waterway.

"Phosphate tests have not dropped yet with legacy sediment issues. However, there has been over 2cum of sediment removed at the trap.

"Turbidity levels have also reduced as the water moves through the wetland. As the site matures, phosphate levels are also expected to drop."

Mr McCall said the strength of the "small" installation lay in its simplicity.

"The overall cost of the wetland, including allowance for farmer time and equipment input at market rates, is estimated at $2000.

"Physical cash costs would be less than half that."

Other trial sites were producing similarly positive results, he said.

This trial would continue for another two years, and results would be shared to promote continued water quality improvement.

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