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Wetland Performance

Owl Farm is located in the Middle Waikato Freshwater Management Unit under the proposed Waikato Regional Plan Change 1 (Healthy Rivers – Wai Ora).
Our commitment to reduce the amount of sediment, nitrogen, phosphorus and bacteria entering the Waikato river has included the construction of new wetlands and maintenance of existing natural wetlands.
Wetlands improve the quality of the water that passes through them – they are often referred to as the kidneys of the environment. They can:
Reduce suspended solids:  By slowing water velocity, solids are able to settle in the deep wide areas of a wetland.
Reduce nitrogen:  Microbes in the wetland sediments attach to live and dead plants below the water and convert dissolved nitrate into nitrogen gas.  Nitrogen gas makes up around 80% of the atmosphere and is harmless.
Reduce phosphorus:   Phosphorus is taken up by wetland plants and can then be buried in the sediments. Phosphorus can also be adsorbed to the wetland sediments.
Reduce harmful microbes and pathogens:  Sunlight is an important sanitizer, killing harmful microbes. Competition and predation by beneficial microbes also reduces the number of harmful microbes.
Sequester carbon:  Wetlands can capture and store large amounts of carbon.  This assists the environment by counteracting the addition of greenhouse gases to the atmosphere caused by burning fossil fuels and farming ruminant livestock.
Improve biodiversity:  Wetlands provide a range of habitats for native species, including plants, birds, fish and insects.
Be aesthetic:  Natural wetlands often have many attractive features. These can include open water areas, diverse plant and animal assemblages and native trees.
Owl Farm has two natural stock-excluded planted wetlands and one constructed wetland area. The constructed wetland was created in 2016 with co-funding from the Waikato River Authority and Waikato Regional Council with support from Opus and Lincoln Agri-tech.
The wetland area is 3400m2 (4.5% of the catchment area), constructed in four cells with a catchment area of 7.6 ha planted with approximately 2500 native species.
Nitrogen removal performance is dependent on how long water stays in the wetland. Normally this requires wetland areas to be around 1-5% of the contributing catchment.
NIWA has been carrying out water quality monitoring from the wetland from 2017-2020 to determine its efficacy. Samples are taken from five well sites, one tile drain site entering wetland and the outflow before entering the Waikato river.
A summary of  the wetland performance shows:
62% reduction in nitrate
49% reduction in total nitrogen
15% reduction in total phosphorus
45% reduction in total suspended solids
A summary of the results and how wetlands function can be found here:  Owl Farm Wetland handout.
Take a video tour of the wetland created by the St Peter’s School Media Squad students: