In 2014 the Baldwins decided to restore to its natural state a wetland his grandfather had turned into a 1.1ha grazing paddock, a wet spot in a shallow bowl surrounded by hills with a stream at one side and the farm's main race on the other.
With funding from the Waikato River Authority and advice from DairyNZ, Waikato Regional Council, Niwa, Opus International Consultants and Hill Laboratories, 12,320 native plants were placed in the wetland. As well as preventing groundwater coming into the wetland, they attract native birds.
The wetland captures runoff from 45ha of surrounding farmland and the race. DairyNZ and Niwa scientists have found that over 12 months, the wetland removed 45 per cent of the nitrogen, 77 per cent of the phosphorus, 80 per cent of sediment and 88 per cent of E. coli.
Those are figures which underline the benefits farmers like the Baldwins – and many more doing the same thing – can bring to improve water quality. It is not only proof of concept regarding the benefits of restoring wetlands (though all farms have different factors in play and need a design specific to those needs), it is reversing a 150-year trend.
According to Landcare Research, more than 90 per cent of New Zealand's wetlands were lost in the past 150 years. The North Island has only 4.9 per cent of its original wetlands left.
For Gray, the wetland project is only one of four major mitigation strategies created to lower their environmental footprint.
"Our farm is located in the Upper Karapiro catchment, which is one of the more sensitive ones in the Waikato region, mainly because it drains directly into Lake Karapiro, where you've got three big water users – Lake Karapiro (the World Rowing Championships and recreation venue), nine Mighty River Power dams and there's 1.5 million people wanting a lot of water coming out of the Waikato River for Auckland city.
"We decided, with all that risk, we were going to get mitigations going reasonably early in the piece."
The first project was planting trees on sidelings (hillsides and riverbanks), because the property is steep for a dairy farm: "Dairy cows don't like walking up hills and when they do, they dislodge sediment which is one of the big contaminants the regional council is trying to control. We planted about 60ha of trees on all our hillsides."
Next, they discontinued brassica cropping - plants like swedes and kale used for feed.
"We had 55ha of brassicas four or five years ago. That is a huge environmental risk because, when you put 800 cows on an acre of land, you've got dung and urine deposition. We're down to 4ha this year and next year there'll be none."
The third project was the wetland and the fourth is the most expensive, most comprehensive and most transformational - construction of a feed pad 18 months ago.
Says Gray: "A feed pad is a million-dollar slab of concrete that includes all the bunkers for maize, silage and lucerne and things that we're feeding these days, and a huge lined pond that we're using to collect all the effluent.
"Most New Zealand dairy farming is based on pasture - dairy cows run to the paddock and eat grass. The big advantage of a feed pad is that you feed them, particularly over the winter, on concrete."
Gray and Marilyn have also introduced once-a-day milking, primarily to improve milk production and fertility – but which has spun off other benefits.
"There's half the effluent to hose off and manage. You save the cows' energy, you save a lot of labour, you save electricity and a lot of costs."
The couple are proud of the progress they've made but responsible farming doesn't end there. Gray says, "We're feeling like a nice family operation, farm succession is all good, we're having some wins on water quality and we're getting some wins on animal welfare. The carbon scenario is the next one we've really got to deal with."
DairyNZ scientist David Burger says he's impressed with how the wetland has performed.
"The fact that we have such very high removal rates and such large removal rates in peak flow events - when we expected the opposite to be true - shows this wetland is very well-designed and that wetlands have a lot of potential as one of the tools in the farmer's toolbox."
The results will go towards draft guidelines to help support other farmers in wetland design. These guidelines will hopefully have local government backing, which will give them confidence when they place them in any future regulations.
He hopes to have 10 similarly constructed wetlands in operation around the country in the next few years so their effects can be measured on different soils and landscapes.
