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Figure 3. Year-by-year changes in regional percentiles for nitrate-nitrogen (NO3-N) in groundwater based on site-specific median values. Y axis scales in mg/L.

Numbers above X axes show the number of sites at which median values could be calculated for the region and calendar year of interest. Horizontal lines on each graph represent the health-related Maximum Acceptable Value (11.3 mg/L) specified in the DWSNZ and the Trigger Value for ecosystem protection (7.2 mg/L) defined in the ANZECC guidelines.

Figure 3. Year-by-year changes in regional percentiles for nitrate-nitrogen (NO3-N) in groundwater based on site-specific median values)

Figure 3. Year-by-year changes in regional percentiles for nitrate-nitrogen (NO3-N) in groundwater based on site-specific median values)

Figure 3. Year-by-year changes in regional percentiles for nitrate-nitrogen (NO3-N) in groundwater based on site-specific median values)

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 2 0.011 0.013 0.015 0.02 0.0 0.0
1997 4 0.002 0.004 0.008 1.26 4.3 5.0
1998 21 0.000 0.003 0.004 0.15 4.9 7.5
1999 23 0.001 0.004 0.020 0.19 4.9 7.7
2000 21 0.000 0.004 0.020 0.19 4.9 8.2
2001 23 0.000 0.002 0.020 0.12 5.3 8.5
2002 22 0.000 0.001 0.011 0.18 5.8 8.2
2003 22 0.000 0.000 0.000 0.36 6.4 9.3
2004 22 0.000 0.000 0.006 0.45 7.3 9.3
2005 22 0.000 0.000 0.003 0.18 7.7 9.3
2006 21 0.000 0.000 0.001 0.07 8.6 9.2
2007 22 0.000 0.000 0.003 0.08 9.1 9.5
2008 23 0.000 0.002 0.005 0.10 9.4 9.8
Change in Percentile Value Over Time2   -4.5E-05 -4.3E-04 - - 0.54 0.28

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3b) Bay of Plenty Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 44 0.002 0.006 0.07 0.2 3.0 11.1
1996 48 0.001 0.004 0.08 0.3 3.5 12.3
1997 53 0.001 0.004 0.06 0.5 3.4 11.5
1998 52 0.001 0.002 0.07 0.5 2.8 8.3
1999 12 0.005 0.019 0.19 1.8 7.3 13.3
2000 12 0.030 0.067 0.25 1.5 2.0 2.1
2001 12 0.015 0.058 0.18 1.3 1.8 1.8
2002 28 0.003 0.010 0.05 0.4 5.4 10.2
2003 15 0.003 0.015 0.18 1.2 2.2 2.7
2004 48 0.004 0.008 0.05 0.5 4.6 10.2
2005 45 0.000 0.002 0.08 0.6 5.0 10.6
2006 47 0.003 0.012 0.11 1.4 4.4 9.6
2007 38 0.002 0.007 0.15 1.1 4.1 5.3
2008 41 0.000 0.003 0.05 0.7 3.8 5.1
Change in Percentile Value Over Time2   - - - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3c) Canterbury Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 184 0.184 0.50 2.70 5.40 9.2 22.0
1996 201 0.180 0.60 2.45 5.25 9.0 19.0
1997 219 0.207 0.49 2.60 4.90 8.3 14.0
1998 219 0.220 0.96 2.60 5.23 8.4 17.0
1999 250 0.240 0.90 2.80 5.30 9.2 20.0
2000 265 0.215 1.70 3.80 6.26 11.3 33.0
2001 265 0.300 1.65 3.80 5.90 10.9 14.1
2002 270 0.304 1.40 3.40 6.20 10.7 16.9
2003 270 0.300 1.30 3.40 5.80 11.7 24.4
2004 273 0.296 0.90 3.60 6.00 11.1 22.4
2005 277 0.200 1.20 3.60 6.35 10.8 13.7
2006 278 0.400 1.40 3.80 6.88 11.6 22.0
2007 276 0.200 1.00 3.25 6.40 10.8 18.0
2008 286 0.300 1.70 4.10 7.43 13.2 20.9
Change in Percentile Value Over Time2   0.01 0.07 0.12 0.15 0.26 -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3d) Data not available

(Figure 3e) Hawkes Bay Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 21 0.005 0.028 0.11 0.43 4.3 5.5
1996 8 0.010 0.015 0.13 0.37 3.9 4.5
1997 39 0.006 0.011 0.04 0.69 5.3 6.4
1998 43 0.003 0.009 0.01 0.53 5.0 5.8
1999 42 0.000 0.001 0.02 0.31 4.8 5.6
2000 41 0.000 0.003 0.05 0.55 4.7 5.5
2001 43 0.000 0.001 0.03 0.62 4.9 5.7
2002 38 0.002 0.021 0.05 0.38 4.4 6.4
2003 43 0.003 0.011 0.10 0.74 4.7 6.1
2004 41 0.005 0.011 0.05 0.54 4.9 5.9
2005 42 0.005 0.011 0.03 0.85 5.1 7.0
2006 43 0.003 0.017 0.07 0.80 5.4 7.6
2007 43 0.003 0.034 0.17 0.70 5.3 7.8
2008 43 0.006 0.022 0.11 0.83 5.3 6.4
Change in Percentile Value Over Time2   - - - 0.03 0.07 0.16

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3f) Manawatu-Wanganui Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 2 0.010 0.245 1.70 3.60 20.0 36.5
1996 3 0.005 0.415 1.70 4.00 16.5 36.5
1997 3 0.009 0.190 1.30 2.80 17.5 35.5
1998 9 0.025 0.240 4.30 12.50 25.9 37.0
1999 12 0.020 0.520 3.40 10.00 24.3 35.0
2000 7 0.013 0.330 4.05 10.00 30.6 33.0
2001 7 0.030 0.255 4.43 12.00 32.0 37.0
2002 2 0.063 0.078 0.15 5.30 11.2 12.6
2003 2 0.010 0.040 0.11 0.31 10.2 12.7
2004 2 0.064 0.080 0.10 0.16 7.5 12.2
2005 2 0.089 0.125 0.17 6.19 11.0 12.2
2006 5 0.015 0.055 0.29 0.76 8.8 43.0
2007 2 0.112 0.118 0.25 3.24 10.1 11.8
2008 2 0.017 0.076 0.15 0.29 0.4 0.4
Change in Percentile Value Over Time2   0.005 -0.023 - - -1.3 -2.4

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3g) Marlborough Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 1 2.200 2.200 2.20 2.20 2.2 2.2
1996 1 1.400 1.400 1.40 1.40 1.4 1.4
1997 4 0.066 0.220 0.42 1.40 5.6 6.6
1998 6 0.083 0.350 1.19 2.20 7.6 10.5
1999 6 0.013 0.050 0.36 0.94 1.7 1.9
2000 6 0.013 0.020 0.32 1.30 7.1 7.9
2001 11 0.027 0.043 0.31 1.00 1.9 2.5
2002 8 0.014 0.040 0.47 1.53 2.2 2.5
2003 12 0.031 0.059 0.51 1.49 2.9 3.0
2004 10 0.045 0.146 0.52 1.35 2.4 2.5
2005 18 0.005 0.055 0.45 1.50 3.5 5.1
2006 20 0.002 0.006 0.30 1.43 4.4 8.9
2007 16 0.002 0.023 0.36 1.33 3.4 10.0
2008 17 0.009 0.052 0.48 2.07 3.6 7.2
Change in Percentile Value Over Time2   -0.007 -0.024 - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3h) Northland Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 3 0.221 0.237 0.57 1.52 3.0 3.4
1997 5 0.005 0.077 0.62 2.61 3.2 3.5
1998 6 0.043 0.123 0.72 1.88 3.2 3.6
1999 6 0.032 0.086 0.22 2.80 3.8 4.2
2000 6 0.007 0.051 0.17 1.42 5.4 7.4
2001 6 0.020 0.108 0.17 6.29 9.6 9.7
2002 10 0.012 0.086 0.30 2.43 8.1 9.5
2003 20 0.002 0.013 0.41 2.80 7.3 8.5
2004 26 0.003 0.024 1.09 2.93 7.4 10.0
2005 26 0.002 0.008 1.13 4.58 7.7 9.8
2006 27 0.001 0.007 0.67 4.57 8.5 9.5
2007 31 0.001 0.006 0.58 3.92 8.6 37.4
2008 31 0.008 0.033 0.59 2.86 8.7 16.6
Change in Percentile Value Over Time2   -0.003 -0.010 - 0.18 0.52 0.99

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3i) Otago Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 28 0.072 0.515 3.00 5.00 26.0 27.0
1996 38 0.035 0.420 0.94 4.13 18.5 25.5
1997 51 0.007 0.193 0.82 2.98 16.7 29.0
1998 70 0.008 0.150 0.66 3.15 12.7 24.5
1999 68 0.008 0.161 0.88 2.98 10.9 22.0
2000 75 0.007 0.133 0.72 3.03 7.3 29.0
2001 78 0.008 0.104 0.75 2.40 6.4 20.5
2002 75 0.007 0.063 0.65 2.35 10.4 27.5
2003 78 0.011 0.150 0.74 2.55 8.8 24.8
2004 71 0.016 0.166 0.82 2.53 6.0 24.8
2005 71 0.013 0.165 0.82 2.64 7.5 25.3
2006 74 0.009 0.107 0.66 2.74 5.5 27.6
2007 72 0.018 0.093 0.69 2.51 5.3 28.6
2008 60 0.013 0.112 0.80 2.65 145.6 231.0
Change in Percentile Value Over Time2   - -0.014 - -0.07 -1.1 -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3j) Southland Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 0            
1997 0            
1998 4 0.61 1.4 4.5 5.9 9.1 11.0
1999 3 0.38 1.0 2.4 4.9 6.2 6.6
2000 13 0.20 1.9 4.4 5.8 7.2 30.0
2001 13 1.03 2.2 4.4 6.6 9.2 14.5
2002 18 0.19 1.8 3.2 6.3 9.9 37.0
2003 21 0.50 1.3 2.6 5.5 9.2 33.5
2004 16 0.84 1.8 3.4 6.7 9.4 9.9
2005 20 0.52 1.7 4.2 6.5 12.0 13.0
2006 21 0.03 1.3 3.3 5.4 8.2 10.5
2007 20 0.04 1.3 2.8 5.0 8.3 12.0
2008 31 0.01 1.4 4.9 9.1 17.0 49.5
Change in Percentile Value Over Time2   - - - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3k) Taranaki Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 16 0.020 0.274 4.28 11.19 45.0 65.0
1996 16 0.011 0.105 1.57 7.90 20.1 58.4
1997 16 0.005 0.034 1.22 5.09 12.6 30.2
1998 14 0.011 0.121 2.54 7.14 11.3 33.9
1999 13 0.027 0.167 2.23 7.93 14.2 36.8
2000 11 0.009 0.056 0.74 3.94 11.0 39.7
2001 28 0.046 0.248 1.47 5.46 16.2 33.2
2002 34 0.012 0.050 1.30 3.67 20.1 30.3
2003 13 0.010 0.175 2.35 8.13 21.8 35.8
2004 22 0.019 0.110 0.72 7.43 18.6 36.1
2005 23 0.002 0.013 1.67 9.21 16.3 27.1
2006 35 0.020 0.643 2.66 8.24 18.4 35.7
2007 34 0.008 0.180 2.64 7.64 18.0 31.3
2008 22 0.043 0.950 5.79 11.80 167.6 295.0
Change in Percentile Value Over Time2   - - - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3l) Tasman Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 8 0.01 0.3 1.5 6.5 18.0 20.2
1996 10 0.01 0.3 2.1 2.9 17.5 20.7
1997 10 0.05 0.2 1.4 2.6 17.1 20.5
1998 9 0.05 0.3 1.0 2.8 16.8 19.5
1999 10 0.04 0.4 1.9 6.3 16.5 19.2
2000 10 0.01 0.1 2.3 2.8 16.6 19.5
2001 10 0.17 0.6 1.6 2.2 16.4 19.3
2002 13 0.05 0.3 2.1 5.6 15.7 18.3
2003 16 0.04 0.3 1.5 3.7 14.1 17.0
2004 16 0.07 0.3 1.7 4.0 14.7 17.0
2005 16 0.01 0.2 1.4 3.2 14.0 16.3
2006 16 0.06 0.4 1.5 3.9 13.4 15.6
2007 16 0.03 0.4 1.2 4.0 13.2 15.0
2008 16 0.02 0.3 1.6 4.6 13.1 16.0
Change in Percentile Value Over Time2   - - - - -0.39 -0.47

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3m) Waikato Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 27 0.377 2.788 5.47 8.53 19.1 22.6
1996 29 0.483 2.566 4.94 8.17 17.1 25.6
1997 30 0.361 2.005 4.60 8.43 16.6 28.2
1998 23 1.531 4.678 6.40 10.66 19.6 32.0
1999 21 0.361 3.486 6.28 9.85 15.6 36.0
2000 19 1.359 3.818 7.25 10.32 16.8 34.0
2001 24 1.473 2.995 4.85 11.75 18.5 35.0
2002 34 0.428 1.968 4.25 11.86 21.2 35.0
2003 55 0.270 1.610 3.74 7.83 19.8 34.0
2004 55 0.202 1.528 3.74 9.19 16.9 31.1
2005 56 0.065 0.670 3.54 7.38 13.8 35.3
2006 63 0.151 1.070 3.89 7.91 14.7 52.4
2007 61 0.140 1.200 3.74 7.50 14.1 25.0
2008 64 0.094 0.870 4.20 8.10 16.0 27.0
Change in Percentile Value Over Time2   -0.017 -0.104 - - - -

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3n) Wellington Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 17 0.010 0.129 0.665 2.79 14.2 15.0
1996 23 0.029 0.307 0.910 3.39 13.7 14.4
1997 31 0.012 0.033 0.755 3.42 13.0 13.4
1998 50 0.001 0.008 0.255 2.08 11.8 13.0
1999 50 0.002 0.010 0.380 3.71 11.2 13.1
2000 51 0.002 0.010 0.560 3.50 11.1 12.7
2001 47 0.001 0.007 0.173 3.19 10.7 12.5
2002 47 0.028 0.065 0.590 3.20 10.8 12.2
2003 47 0.004 0.021 0.658 3.86 10.1 11.4
2004 61 0.004 0.017 0.985 4.10 10.8 12.3
2005 69 0.001 0.005 0.557 3.18 10.4 11.0
2006 68 0.001 0.004 0.635 3.48 10.0 11.3
2007 67 0.002 0.005 0.576 2.50 10.0 10.4
2008 67 0.002 0.014 0.605 2.65 9.8 11.0
Change in Percentile Value Over Time2   - -0.002 - - -0.304 -0.305

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.

(Figure 3o) West Coast Region calculated percentiles and maximum values for nitrate-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 0            
1997 0            
1998 6 0.456 0.589 0.78 0.94 1.4 1.6
1999 7 0.268 0.745 0.99 1.30 1.7 1.8
2000 7 0.298 0.845 0.93 1.39 1.8 1.8
2001 7 0.294 0.810 0.93 1.64 2.3 2.4
2002 6 0.315 0.965 1.28 2.09 3.1 3.3
2003 7 0.359 0.985 1.50 2.15 3.1 3.3
2004 8 0.394 0.950 1.10 2.23 3.3 3.7
2005 8 0.366 0.813 1.01 2.35 3.7 3.8
2006 8 0.398 0.841 1.18 2.99 3.7 3.8
2007 8 0.330 1.006 1.40 3.58 5.0 5.1
2008 8 0.376 1.038 1.58 3.83 5.8 5.9
Change in Percentile Value Over Time2   - 0.032 0.05 0.26 0.4 0.4

1 Total number of sites for which a median value could be calculated (i.e. parameter had been measured at least once at the site in question within the calender year of interest).

2 Trend tests performed on calculated percentile values for the years 1995 to 2008. A null value (-) indicates that no significant trend was detected at the 95% confidence interval. Numbers are in units per year and indicate significant trends. Negative numbers indicate a decreasing trend.