Nitrate vulnerable zones: a new methodology

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Nitrate vulnerable zones (NVZs) are areas designated as impacted, or at risk of impacts, by agricultural nitrates applied as fertilisers to boost crop yields. In the past, the process of designating an area as a NVZ has been perceived to be reliant on a limited amount of data and lacking in transparency.

We have responded to these concerns with the development of a new methodology which is more scientifically robust and well documented. It has also achieved approval by all of the stakeholders in the NVZ review group, which includes the Scottish Government, the National Farmers Union Scotland (NFUS), Scottish Natural Heritage (SNH) and Scotland’s Rural College (SRUC).

It is important to protect areas of groundwater which are vulnerable to nitrate contamination as it can present a risk for drinking water supplies – especially private supplies – and also causes eutrophication of water bodies. Eutrophication is the process through which the oversupply of nutrients (in this case, nitrate) causes explosive growth of plants and algae in a water body. When these organisms die, they are broken down by bacteria which use up the available oxygen in the water.

TractorThe main source of nitrate impacting on the water environment is the application of fertilisers to land. Nitrate can leach into groundwater if too much fertiliser is used on crops, or if it is applied during unsuitable weather conditions. Other potential sources of nitrate include: leaks from slurry stores; contaminated run-off from farmyards and steadings; waste water treatment works and septic tanks.

The Scottish Government is currently completing a review of areas designated as NVZs. These reviews are carried out regularly to ensure that environmental improvement measures are focused in the right places. This will be the first to be based on the new methodology, which has been developed by SEPA in consultation with the Scottish Government, NFUS, James Hutton Institute (JHI) and British Geological Survey.

This methodology is based on the risk assessment process we already use to comply with the Water Framework Directive (WFD). The WFD is a European Union directive under which we have a duty to assess a broad range of risks to the quality of groundwater, including those from nitrates produced by agricultural activities.

We use water quality data from our monitoring network to find out the current condition of the water environment and how much risk there is for the quality to drop in the future. Information from other sources (including modelling data from JHI and water quality data from private water supplies provided by the Drinking Water Quality Regulator) is used to give a confidence level to our initial assessment.

When the different sources of data show similar results, we can assign the assessment a high confidence. When there are big differences, low confidence is assigned. We will only recommend changes to NVZ designation in cases where there is high confidence in the nitrate assessment results.

Development of the methodology has been made possible by close collaboration between our Water Resources Unit (WRU) and Land Unit, the Scottish Government and external partners, particularly the NFUS. The resulting assessment relies on the valuable work done by WRU assistant scientists and National Monitoring Team samplers in the field, and the analytical skills of our chemists in the lab.

NVZ mapThe use of the new process is already proving its effectiveness and has provided evidence that nitrate risks are low enough in some areas, particularly in parts of Aberdeenshire, Perth and Kinross, Fife and the Borders, to propose removal of their designation as NVZs.

There is also new evidence that in two areas, one in Angus and one in Galloway, groundwater is at sufficient risk of nitrate pollution for NVZ designation to be proposed.

Overall, the proposals would reduce the current area of NVZ designated land in Scotland by 25%.

The new methodology is robust and reliable, while also providing a more efficient approach in addressing the requirements of both the Nitrates Directive and the Water Framework Directive in a single, integrated process. Feedback from the NFUS and other external stakeholders has been encouraging, and the Scottish Government has decided to use the methodology for NVZ reviews going forward.

The results of the assessment will be used to drive ongoing changes to our monitoring plan, and to make sure that we continue to keep track of risks to the water environment in the future.

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