Murray Wards said the point of the Gore Catchment Group’s Community Open Day last week, on his Waimumu farm, was to show how easy it was to build a small, yet effective, wetland.
But it was time-consuming, and after starting the project on January 31, he spent "too much" time on the digger excavating the pond, totalling about 200 hours.
It started filling up with water by Easter and he was going to wait until the project was more established before testing the water, but could not help himself.
In his testing, he noticed that water going into the wetlands, which took a month to pass through, was coming out the other side with an average of 30% less nitrogen.
"It was working right from the start," he said.
Nitrates were not as much of an issue for his area as they were at the bottom of the valley of Gore.
"Nitrates off the farm run about a 1 [milligram per litre]," he said.
The small pond was more so designed to filter phosphorus from the water, as phosphorus in freshwater caused harmful algae to bloom such as that present in the Mataura River, he said.
The small project had turned into a larger educational one and there were two planting sessions with Enviroschools run by Environment Southland.
The programme was in action again last week, led by Environment Southland education adviser Jane Tagomoa, who helped schoolchildren plant makomako and kahikatea around the wetlands.
There was also an educational session for adults in which Mr Wards, Dairy NZ environment manager Justin Kitto and farmer Lee Baldwin spoke on the "dos and don’ts" of building your own wetlands.
Mr Kitto said it was important the man-made pond had a "slow and meandering path", which allowed the desired nutrient-filtering process to take place.
"The longer the water is in contact with the plant matter, the longer it is naturally purified," he said.
Ms Baldwin, who is also a certified nutrient management adviser, likened nitrates to teenagers who would not stay put, or an escape artist like Houdini.
She categorised phosphorus as the "grandma" of the nutrient world, as it did not like to move much — and if it did, something had gone quite wrong, she said.
Cow urine, fertiliser and certain types of feeds added to the nitrate content in soil, which was leached into freshwater, and heavy rains pushed the nutrient into the soil profile, she said.
Wetlands were the answer and Southland’s natural filter, she said.
