A new report from the Environmental Protection Agency (EPA) on the need for reductions in nitrogen concentrations has found that agriculture is responsible for 85% of nitrogen leakage into predominantly rural catchments.
The report entitled, Assessment of the catchments that need reductions in nitrogen concentrations to achieve water quality objectives highlights elevated concentrations of nutrients (nitrogen and phosphorus) as the primary water-quality issue of concern in Ireland.
Excess nitrogen leaches through freely draining soils, into groundwater, and then into our rivers and streams.
Increased concentrations cause an increase in the growth of algae and aquatics plants, which impacts drinking water and aquatic ecosystem health.
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Nitrogen concentrations in waters have been increasing since 2013 and the key catchments of concern are in the south and south east of the country.
As a result of the report, a number of maps have been created to highlight the highest-risk areas caused by agriculture leaches – chemical and organic (manure and urine) fertilisers – to waters.
According to the report, nitrogen also comes from urban and domestic waste water, but the amount from human sources is much smaller overall than that caused by agriculture.
“At the national scale, there is a broad relationship between the numbers of
livestock on land, the amount of nitrogen fertiliser used, and nitrogen emissions in waters.
from 1990 to 2020, at the national scale. Image source: EPA
“However, at the local scale, the soils and the climate are also very important driving factors that dictate how much of the nitrogen used on land ends up in waters from any given farm, in any given year.
“Measures, therefore, need to be targeted to achieve the most effective environmental outcomes,” according to the report.
Water quality concern – EPA
Although there are controls in place to help achieve our water quality objectives – Nitrate Directive, Good Agricultural Practice for Protection of Waters Regulations, Surface Water Regulations, and Drinking Water Regulations – additional measures may be necessary, the report found.
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Only 38% of our estuaries – these are particularly sensitive to elevated nitrogen concentrations – are meeting their water-quality targets.
“Due to the large variability in farming practices, soils and climatic conditions across Ireland, the source-input controls may not be sufficient in some places to achieve the nitrogen limits set in waters. In these situations, supplementary measures may be needed to protect an improve water quality.”
Eighteen major river catchments were monitored by the EPA of the purpose of this report.
Thirteen, all located along the south, southeast and east coasts, were found to have elevated nitrogen concentrations and are key catchments of concern.
These include:
- Maigue/Deel;
- Bandon;
- Lee;
- Blackwater;
- Suir;
- Nore;
- Barrow;
- Slaney;
- Tolka/Liffey (including the Dodder);
- Boyne.
The 2019 concentrations were higher than the 2009 concentrations in all but two of the 18 catchments.
Climate – EPA report
Climate’s role, the report noted, was particularly evident in 2018-2019 with the dry summer conditions in 2018 leading to “higher levels of mineralisation in the soils” in some parts of the country.
At this time, farmers also applied additional fertiliser to try to encourage grass to
grow, the EPA report said.
The report continued:
“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. 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.”
Load reductions
The Barrow and the Slaney catchments needed the highest levels of nitrogen reduction in most years, according to the report.
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.
“The main factors driving the variability in agricultural catchments between years are changes in the weather, especially temperature and rainfall which affect growing conditions, uptake of nutrients, and nutrient transport and dilution; and changes in farm practice including the farming system, intensity, day to day management practices, and management of soil fertility, for example.
“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,” the report said.
Variables
There are many variables that determine how much nitrogen from farming ends up in our waterways, the report said. This includes farm practice, soils, climate and losses to air.
“The Teagasc National Farm Survey Sustainability report shows that average nitrogen-use efficiencies in Ireland’s predominantly grass-based farming systems are of the order of 25%.”
This means that 25% of the amount used on land is captured in the food that is produced and the remainder is either available for losses to the environment, whether to air or to water, or is stored in the soil organic matter.
The data 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 the EPA to better link management of nitrogen on farm, to nitrogen emissions in waters.”
Ag Climatise
Over the next 10 years, under the Ag Climatise roadmap, a target has been set for an absolute reduction in the overall level of nitrogen fertiliser being used on Irish farms from a high of 408,000t in 2018 to 325,000t in 2030, with an interim target of 350,000t in 2025.
“It will be important for achieving water quality outcomes that the nitrogen reduction
measures as set out in Ag Climatise for climate mitigation purposes are implemented in the critical source areas for water, so that multiple environmental benefits can be achieved with the same measures,” the report said.