Integrated Water Quality - Neagh Bann & North Western RBDs 2013

The Neagh Bann and North Western River Basin Districts are both international river basin districts covering an area of 2,000 km2 7,400 km2 respectively within the Republic of Ireland.  In comparison to the national picture, while both RBDs perform reasonably well with regard to groundwaters and transitional and coastal waters, they both perform poorly when it comes to rivers and lakes.  In the period 2011 to 2013 the GPC status of 34.1% of all lakes in the country was at least 'good' while in the NWIRBD the figure dropped to 23.1% and further still to 14.3% in the NBIRBD.  The pattern for rivers is similar.  With regard to biological Q value, figures from the period 2010-2012 indicate that 65% of all river stations in the country are at least 'good' status but this figure drops to 49% in the NWIRBD and further still to 35.1% in the NBIRBD.

Nutrient enrichment is the main case of water pollution in both RBDs but it is clear that there are regional variations.  For example there is a much better level of compliance with the ortho-phosphate EQS in the northern half of the NWIRBD (Donegal) compared to the southern half and also compared to the NBIRBD.  However, performance with regard to biological Q values does not follow the same pattern with a more even spread of river stations at less than 'good' status.  This would indicate that there are additional factors (e.g. use of agricultural pesticides) which are impacting on water quality in Donegal.

Analysis of long-term trends which has been carried out in a number of counties indicates that ortho-phosphate levels in rivers have been steadily declining since the 1980s and 1990s.  Despite this, over the same period there has been a marked decrease in the number of biological 'high' status sites in both RBDs.  In addition the trend for the percentage of river stations achieving at least 'good' status is generally downwards as shown below.

 Figure 1 - Long term 3-year rolling trends in percentage of river stations at least 'good' status in the NWIRBD and NBIRBD 1978-2013

Long-term 3-year rolling trends in percentage of river stations at least 'good' status in the NWIRBD and NBIRBD 1978-2013

Agriculture remains the single largest pressure on water quality in both RBDs.  It is regarded as a pressure in well over half of the river stations in both RBDs.  It also includes the use of agricultural pesticides which is suspected to be a significant pressure in some parts of the NWIRBD.  Other pressures such as municipal wastewater, urbanisation and foretry (especially in the NWRBD) are also significant.  In many cases, it is a combination of a variety of pressures that is responsible for water quality issues.

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Integrated Water Quality Report for the North Western and Neagh Bann River Basin Districts 2013