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Agriculture is responsible for 85pc of nitrogen leakage into ‘critical’ river catchments – EPA report 

Agriculture is responsible for more than 85pc of the leakage of nitrogen into ‘critical’ rural water catchments in the south and southeast of the country, a new report on water quality has found.

he EPA report – entitled ‘Assessment of the catchments that need reductions in nitrogen concentrations to achieve water quality objectives’ – was carried out to identify “at risk” areas where nitrogen concentrations “are too high to support” healthy aquatic life under the Water Framework Directive.

As part of the analysis, “critical source area maps” have been developed to “help target” nitrogen control measures in the landscape.

The document, seen by the Farming Independent, describes the annual tonnage of nitrogen discharged from 18 major catchments – including the Maigue/Deel, Bandon, Lee, Blackwater, Suir, Nore, Barrow, Slaney, Tolka/Liffey and the Boyne – out to sea over the last decade.

It states that 13 of these catchments have “elevated” nitrogen concentrations, making them “key catchments of concern” – all of which are located along the south, southeast and east coasts. It says the 2019 concentrations were higher than the 2009 concentrations “in all but two of the 18 catchments”.

“The Suir, the Blackwater, the Slaney and the Barrow have had substantially larger nitrogen loads discharging from their catchments over the whole period than the other catchments.”

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Image source: EPA report June 2021

The Barrow and the Slaney catchments needed the highest levels of nitrogen reduction in most years, both in absolute terms, and as an average per unit area.

“The scale of the reductions needed ranged from zero in some years to just over 8,000t of nitrogen in the Barrow catchment in 2018.

“In the majority of catchments, the reductions needed increased towards the end of the decade, reflecting the increases in concentrations in waters – most catchments recorded the maximum reductions needed during the period 2017-2019,” the report states.

Climate and herd size

In terms of the nitrogen sources, it is stated that “in the predominantly rural catchments, more than 85pc of the sources of nitrogen in the catchment are from agriculture, from chemical and organic fertilisers (livestock manure/urine).

“In contrast, the majority of the nitrogen in Liffey/Tolka catchment, which incorporates Dublin City, is from urban waste water.”

On the farming detail, it analysed the role of climate, which was particularly evident in the 2018-19 figures. It also looked at soil, farm practice and the relationship between herd size, gross nitrogen balance and nitrogen emissions to water.

“The relatively dry summer conditions in 2018 in many parts of the country led to higher levels of mineralisation in the soils. Farmers also applied additional fertiliser to try to encourage grass to grow.

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Image source: EPA report June 2021

“This was followed by a wet autumn, winter and early spring, when the rainfall and rising groundwater levels pushed the excess nitrogen stored in the soils out into rivers and streams. This led to above average concentrations in waters in 2018 and 2019.”

It’s added that the proportion of the nitrogen coming from arable farming “was relatively high” in the Barrow (28pc) and Slaney (27pc) catchments, however the majority of the nitrogen from agriculture across all catchments “was from pasture”.

“Within catchments, the freely draining soils with higher intensity farming are the highest risk areas for nitrogen leaching from agriculture.”

It also highlighted that preliminary estimates suggest that “for every 1t of fertiliser purchased in Ireland, 0.29t of nitrogen is discharged out to sea in our rivers.

“Further modelling work is being carried out by Teagasc and EPA to better link management of nitrogen on farm, to nitrogen emissions in waters,” it says.

Action maps

On actions to reduce nitrogen concentrations in these catchments it says measures should be targeted in the critical source areas in the catchments of concern in order “to deliver maximum environmental benefits”.

“At the farm scale, the soil conditions are an important factor in dictating the level of influence the farm has an on the overall catchment water quality – the most freely draining soils are the most favourable for nitrogen leaching.

“It is important therefore that sufficient resilience is built in to the policy choices, that will keep the nitrate concentrations within sustainable limits for good ecosystem health at all times, whatever the weather.

“The critical source areas are the locations where the risk of nitrogen leaching occurring is the highest, and where the quickest response will likely be seen in the river if measures are implemented.

“These maps can be used to target and prioritise actions in the catchments that need nitrogen reductions, and as a preventative measure in catchments that currently have satisfactory nitrogen concentrations. Some areas may need more actions than others depending on farm practices.”

“There is approximately 6,900 km2 of the highest risk areas across the catchments of concern. This represents 40pc of the total combined areas of the catchments.

“Over the next 10 years, the Ag Climatise roadmap has set a target of an absolute reduction in the overall level of nitrogen fertiliser being used on Irish farms from a high of 408,000 tonnes in 2018 to 325,000 tonnes in 2030, with an interim target of 350,000 tonnes in 2025.

“This is important not only for the purposes of meeting our statutory obligations, but also to support our livelihoods, health and wellbeing, and the production of healthy food.”

This work from the EPA will feed into the fifth Nitrates Action Programme and the third cycle river basin management plan, both of which are currently in preparation.

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