Catchment News

Significant Pressures: Agriculture

Agriculture is the most common land use in Ireland, covering approximately 65% of the country. Through the initial characterisation process, agriculture has been identified as the most prevalent significant pressure, impacting just over half (780) of all water bodies (1,452) that are At Risk of not achieving their water quality objectives (Table 1).

Table 1: Number of At Risk water bodies where agriculture is a significant pressure

Waterbody (WB)	Number of WBs	Number of At Risk WBs	Number of waterbodies with agriculture as a significant pressure	% of WBs with agriculture as a significant pressure	% of At Risk WBs with agriculture as a significant pressure
River	3192	1178	629	19.7%	53.4%
Lake	818	132	80	9.8%	60.6%
Transitional	195	56	32	16.4%	57.1%
Costal	111	13	8	7.2%	61.5%
Groundwater	513	73	31	6.0%	42.5%
	4829	1452	780	16.2%	53.7%

Water quality problems in water bodies impacted by agriculture

Almost half of the water bodies impacted by agriculture are at Moderate status (Figure 2), which means the level of contamination may not be too far away from the Good status target, although 60% of these waterbodies have at least one other significant pressure in addition to agriculture.

The most common water quality problem arising from agriculture is excess nutrients, giving rise to eutrophication. Phosphorus is typically the issue for rivers and lakes, and too much nitrogen for estuaries and coastal waters. Excess ammonium may also be a problem in some waterbodies.

Figure 3 shows the annual average phosphorus concentrations in rivers from 2007 to 2017. The red line is the environmental quality standard (EQS). Mean concentrations below the line are typically required to support good ecological status. Rivers with agriculture as a significant pressure have a higher average phosphate (PO4) concentration compared with the national average. Since 2012, there has been an increase in the phosphate concentrations in rivers with agriculture as a significant pressure. Additional action is going to be needed in these water bodies to reduce the phosphorus losses if Good status is to be achieved.

Nutrient source and losses

Nutrient losses from agriculture can arise from discrete or point sources such as farmyards; or from diffuse sources such as spreading of chemical fertilisers or organic manures.

The initial characterisation process has highlighted that while improvements have been made with managing point sources, significant challenges remain with managing diffuse sources, which are typically more difficult to identify and manage than point sources.

The key to managing diffuse sources is to consider that different contaminants behave differently in the environment and reach water bodies along different flow pathways. The flow pathways are controlled by the soils, subsoils, bedrock and the presence/absence of drains and ditches. For example, diffuse phosphorus loss occurs most often via overland flow on poorly draining soils and subsoils, such as those found in parts of Cavan, Monaghan, Wexford, Limerick and Meath.

Nitrogen loss on the other hand, occurs in freely draining settings where it infiltrates first into groundwater, before discharging into linked river systems and traveling down to the estuaries and coastal waters. Cork, and parts of Tipperary, Kilkenny, Carlow and Wexford are particularly susceptible to nitrogen losses from agriculture.

As a result, different solutions or mitigation options will be required to tackle the different contaminants.

Possible solutions

The mitigation actions will vary depending on

1. the contaminant impacting the water body, and
2. the pathway linking the contaminant from the agricultural activity to the water body.

Phosphorus mitigation actions are best targeted at intercepting the overland flow pathways. This is because it takes just a tiny fraction of the phosphorus that would normally be applied to land to cause a water quality problem, and source control measures will not be effective enough on their own. Pathway control actions may include targeted planting of hedges and woodland along rivers, riparian buffer strips and constructed wetlands. For nitrogen, the mitigation actions will need to be targeted at controlling the loss at source because the pathway into groundwater is more difficult to intercept. Source control actions include nutrient management planning in particular correcting soil pH and fertilizer placement technologies. Mobilisation control sources such as catch crops, use of clover, and precision application of fertiliser may reduce the mobility of the contaminant.

Sediment

Biological monitoring has identified excess fine sediment as an issue in some places. Fine sediment fills the spaces between larger gravels in the stream bed and can interfere with aquatic ecosystem functions, particularly in the more sensitive high status waters. Some species, like the endangered Freshwater Pearl Mussel, are especially sensitive to sediment. Sediment is also often the transport mechanism for chemicals and nutrients that are attached to the sediment particles.

Typical sources of sediment from agricultural activities include, runoff from ploughed or arable land and farm roadways, erosion of river banks at cattle access points, and land drainage and channel maintenance. Mitigation options might include livestock exclusion, fencing the riverbank, attenuation ponds and careful management of ditches and drainage.

The Next Steps

In the River Basin Management Plan 726 water bodies are being targeted in 189 Areas for Action, and agriculture has been identified as a significant pressure in almost half of these water bodies.

In these Areas for Action the Local Authority Waters Programme Catchment Assessment Team has been established to undertake further assessment to determine precisely what and where the activities causing the problems are. The Catchment Assessment Team will work closely with thirty new specifically trained agricultural sustainability advisors from Teagasc and the dairy Co-ops to identify possible solutions, or mitigation options. The agricultural advisors will work with farmers to find the best farming practices and any suitable mitigation actions that can be implemented to prevent contamination occurring.

Undoubtedly, there is a lot of work ahead and the success of this process will depend on building partnerships, trust and learning from one another – both between organisations, and with the communities living in the Areas for Action. Individual organisations can achieve improvements in water quality, but by working together we will achieve more sustainable improvements.

EPA Catchments Unit

Learn more:

You can view the individual water bodies where agriculture is a
significant pressure on www.catchments.ie/maps

For planning and policy, including measures, see
www.bit.ly/rbmp20182021