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Water
45
Nitrate and Phosphate
in Groundwater
Figure 4.1 illustrates trends in nitrate
levels. In the period 2008–2009
there was a general reduction in
nitrate concentrations compared
with the previous period, which
has been attributed to increased
rainfall, reductions in inorganic
fertiliser usage, improvements in
organic fertiliser storage and the
implementation of land-spreading
restrictions. In comparison with
2009, the slight increases in nitrate
concentrations that are observed
in 2010 are attributed to reduced
rainfall leading to less dilution of
the nutrients in the water body
(McGarrigle et al., 2010).
Elevated nitrate concentration in
groundwater remains an issue,
particularly in the southeast and
south of the country. It may
contribute to eutrophication of
surface waters and impact on the
quality of water abstracted for
drinking water. Elevated phosphate
concentrations in groundwater,
resulting from diffuse pressures, can
also be a cause of eutrophication of
rivers and lakes where the source of
phosphate is not attributed to point
source discharges, especially at times
of low flow. Previous EPA water
quality reports (1994–2010) have
reported diffuse agricultural pollution
as a significant source of the elevated
nitrate and phosphate concentrations
in Irish groundwaters.
River Water Quality
Over 13,000 km of river channel is
assessed by the EPA on an ongoing
basis at over 2,500 sample points.
The most recent assessments show
that approximately 71% of river channel
is classed as unpolluted in Ireland –
achieving at least good ecological
status. However, approximately 29%
of monitored river channel length is
polluted to some degree (Figure 4.2).
Long-term trends in river quality from
1987 to 2011 are shown in Figure 4.2.
The main trends show that there has
been:
n
an overall decrease in the length
of river channel that is classed
as unpolluted, although there
have been some improvements in
recent years
Figure 4.1
Trends in Nitrate Concentrations at Groundwater Monitoring Locations 1995–2010 (Source: EPA)
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
2010
2009
2008
2007
2004-2006
2001-2003
1998-2000
1995-1997
% Monitoring Locations
> 50
37.5 - 50
25 - 37.5
10-25
5-10
< 5
Figure 4.2
National Trends in the 13,188 km Baseline Showing the Percentage of Surveyed River Channel in the Four EPA
Biological Quality Classes (Source: EPA)
0
10
20
30
40
50
60
70
80
90
100
2007-’11
2007-’09
2004-’06
2001-’03
1998-’00
1995-’97
1991-’94
1987-’90
Class A: Unpolluted
% Surveyed Channel length
Class B: Slightly Polluted
Class C: Moderately Polluted
Class D: Seriously Polluted