Clean water project aims to solve farm pollution problems
- Credit: Sonya Duncan
A Norfolk farm has found cheap and simple ways to reduce pollution as part of a project to improve the quality of the water leaving its fields and ditches.
The Morley Agricultural Foundation (TMAF) launched its "clean water project" in late 2018 at its 700ha arable farm at Morley near Wymondham.
Since then it has successfully installed measures including V-notch weirs and new ponds to trap silt and reduce run-off.
Farm manager David Jones said although there are many reasons for water pollution, including roads and domestic sewage treatment works, farms needed to take whatever action they could to prevent soil particles and nutrients such as nitrogen and phosphates from entering watercourses.
The TMAF project focuses on finding solutions which are achievable for any farm.
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"Whatever we do has to be modest in cost and, if possible, done with in-house farm equipment and labour," said Mr Jones. "It requires many landowners to make small changes in practices to make big changes to our overall water quality."
Among the new features at the farm are V-notch weirs, small dams placed in ditches to hold back 150-200mm of water. When the flow level is low the water trickles through the lowest part of the V shape, and during heavy rainfall as the water level moves up the V, it can flow faster.
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"The idea is that a pool is formed behind the dam, the water moves much slower and so the silt falls to the bottom," said Mr Jones. "Depending on the silt loading it can be dug out periodically, in our case every two years.
"A similar thing can be achieved by not maintaining ditches but if left indefinitely there becomes a point where as a drain nothing works properly. The risk of flooding land and property can be much higher. The V-notch weir is a more managed approach to reducing silt movement."
The theory was tested with plywood weirs costing £8 each, which have since been replaced with more permanent metal ones costing about £100 each.
Elsewhere on the farm, a wetland improvement has been carried out with the support of the Norfolk Rivers Trust and Anglian Water, which part-funded the work.
Mr Jones said effluent from a treatment plant flowed through one of the farm's ditches into a "large wet hole, maybe a former quarry for clay and flints".
In 2019, three ponds were dug by simply using soil to make bunds, with pipes installed so the water could drain through. The first pond is about 1.5m deep, and the second is about 250mm and planted with a variety of aquatic plants such as lesser pond sedge, water mint and bur reed. The third pond was already full of bulrushes and nettles.
"As the water level rose the nettles died back and the bulrushes flourished," said Mr Jones. "The aim is to keep the water in the ponds a long as possible where the actively growing roots interact with populations of denitrifying bacteria in the mud which use up the nitrogen."
TMAF is being assisted by Cathy Munford, a mature student taking an MSc in environmental sciences at the UEA, who is researching the effect of the integrated constructed wetland in mitigating nitrate and phosphate pollution from the waste water treatment plant.
"The initial results from August to November are encouraging as both nitrate and phosphate have been reduced as water progresses through the wetland," said Mr Jones. "This is a pleasant surprise as larger areas and more time for establishment are usually needed for wetlands to be effective.
"Populations of denitrifying bacteria, which use and remove the nitrate, take time to build up in the anoxic (oxygen-free) conditions in the mud, but it appears that a large vigorous population of bulrushes in the third pool are removing nitrate from the water."