Farmers in Dorset have been set water quality targets to reduce the level of nitrogen in Poole Harbour.

The amount of nitrogen entering the harbour has more than doubled, from around 1,000 tonnes/year in the 1960s to around 2,300 tonnes/year now.

This has led to the mudflats becoming covered in green algae.

Water quality has deteriorated and wildlife is being affected.

Starting this year, farmers in the area have to report their compliance and nutrient loss to the Environment Agency (EA) or the independent body overseeing a new scheme.

The new scheme follows the publication of the Environment Agency and Natural England’s Poole Harbour Consent Order Technical Recommendations (PHCOTR), which sets new interim nitrogen and phosphorus targets for the catchment.

PHCOTR states that nitrogen loads which reach the harbour should be reduced from around 2,300 to 1,500 tonnes/year, and ortho-phosphate (OP) loads should be reduced from around 51 to 22 tonnes/year.

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As agriculture contributes the largest source of nitrogen to the catchment, and a significant amount of phosphorus, the EA has set farmers new emission limits and measures.

Farmers are being told to start to plan and implement measures to achieve these objectives, and from 2023 farmers will need to ensure their nutrient losses across their farm holding (or group of farm holdings) do not exceed 18.1 kilogram/hectare/year nitrogen.

Where a farmer joins an EA approved scheme they need to meet alternative glide path targets which will achieve the emission target by 2030.

In such a scheme, all farmers are incentivised to maximise efficiency (and no farmer can apply above crop need), but farmers that have reduced their losses below the glide path can trade nitrogen credits to farmers looking to offset some of their nutrient losses.

The EA is offering new tools to calculate the amount of nutrients they are losing to the environment, including the Nitrate Leaching tool (NLT) and Agricultural Compliance Tool (ACT).

Farmers will need to use these tools each year to ensure their nutrient plan and farm practices meet these new emission limits and requirements.

Poole Harbour is designated as a Special Protection Area (SPA), Site of Special Scientific Interest (SSSI) and Ramsar site.