Plans to convert a 142ha farm into a massive wetland are critical to the hopes of restoring Lake Horowhenua.
Michelle Sands, HortNZ environment manager, says water quality in the lake is so poor it has caused "a lot of sadness in the community" – but plans to develop a wetland near the lake on land currently run as a farm comes at a critical time.
"I believe there is still an opportunity to turn things around and restore not only the water quality, but the sense of pride locals have about the lake," she says. "It is in a poor state but is not as bad as some other lowland lakes because it still contains macrophytes (aquatic plant species that provide food and cover for fish and other wildlife and which produce oxygen).
"I think it is not impossible, that in a few years, we will see a real turnaround in the lake's condition."
The wetland will create a swamp and forest habitat for birds and fish – an echo of the wetlands that were once numerous in the Horowhenua area. However, a start on planting is probably still at least a couple of years away, she says, when the purchase of the farm will be completed.
Vegetable-growing land in the area sits on a terrace of highly fertile soil above the low-lying dairy farm that the wetland will replace – and Sands says the water quality treatment function of the wetland will complement other steps growers are taking.
Among these is the development and fine-tuning of farm environment plans (FEPs) to improve growing practices. So far seven growers, representing 90 per cent of the growing area, have certified FEPs and have had them independently audited. A further six are currently preparing plans for audit and certification.
The plans help growers look at ways to reduce sediment and nutrient run-off (construction of sediment ponds and buffer strips are among solutions being suggested) while the implementation of soil testing prior to planting is helping establish "careful application of fertiliser".
Sands says a mild climate and good soil in Horowhenua make it one of the best places in New Zealand for horticulture. More than 38 vegetables - including cabbages, leafy greens, Chinese greens, salad crops, potatoes and onions - are grown on a total of 500ha by the catchment's 13 growers.
"This growing is vital to New Zealand's supply of fresh, healthy food," she says. "It has national benefits but a local impact, and with good freshwater planning and investment, the country can have both healthy vegetables and water."
Located just 2km west of the lower North Island town of Levin (population 18,800), the lake was once an important source of food for local iwi and a popular recreational playground. Over many decades it has suffered from the effects of sediment and nitrate leaching from nearby sheep and beef and dairy farms, major horticulture operations and the impact of stormwater and urban wastewater run-off.
Sheep and beef farms cover about 43 per cent of the lake's total 7000ha catchment while dairying takes up about 19 per cent. The catchment is also one of New Zealand's most important horticulture areas, with 13 vegetable growers producing about 10 per cent of the country's supply of green vegetables.
The wetland will be constructed in a corridor between Lake Horowhenua and Lake Papaitonga after the purchase of the farm by the government and Horizons Regional Council. A number of community groups and land users, including dairy farmers, are involved in the project, made possible following an injection of $11.2m from the government's Jobs for Nature programme. The council also contributed $1m.
Sands says HortNZ is supporting the wetland development - born out of iwi, growers and the Levin community coming together with the support of local, regional and central government. HortNZ is also helping vegetable growers institute other measures to reduce the impact on the environment.
"The Tararua Growers Association saw an opportunity to be involved in the wetland project and are one of several organisations working to bring it about," she says. Others include Woodhaven Gardens, Ngāti Raukawa and Muaūpoko iwi, Massey University, Horowhenua District Council, Horizons Regional Council, Lake Horowhenua Trust and dairy farmers.
"Creation of the wetland will improve the health of the lake by treating the water that flows into it from the Arawhata Stream," Sands says. "About 30 per cent of the nitrate load in the lake comes from vegetable growing operations but (reducing) this in itself won't be enough to turn the lake around, as improvements will need to be undertaken on a catchment-wide scale."