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Figure 4. Year-by-year changes in regional percentiles for ammoniacal-nitrogen (NH4-N) in groundwater, based on site-specific median values. All 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 aesthetic Guideline Value (1.5 mg/L) specified in the DWSNZ and the Trigger Value for ecosystem protection (0.9 mg/L) defined in the ANZECC guidelines.

Figure 4. Year-by-year changes in regional percentiles for ammoniacal-nitrogen (NH4-N) in groundwater, based on site-specific median values

Figure 4. Year-by-year changes in regional percentiles for ammoniacal-nitrogen (NH4-N) in groundwater, based on site-specific median values

Figure 4. Year-by-year changes in regional percentiles for ammoniacal-nitrogen (NH4-N) in groundwater, based on site-specific median values

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(Figure 4a) Auckland Region calculated percentiles and maximum values for ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0
1996 2 0.250 0.250 0.250 0.250 0.250 0.250
1997 4 0.061 0.103 0.170 0.253 0.331 0.350
1998 21 0.009 0.030 0.160 0.295 0.898 1.500
1999 23 0.010 0.020 0.160 0.275 0.743 1.600
2000 22 0.007 0.020 0.170 0.270 0.781 2.800
2001 23 0.006 0.010 0.160 0.260 0.952 1.500
2002 23 0.008 0.025 0.160 0.260 0.920 1.300
2003 22 0.005 0.010 0.173 0.310 1.150 1.600
2004 22 0.006 0.010 0.173 0.271 1.102 1.450
2005 22 0.010 0.028 0.170 0.263 1.056 1.380
2006 21 0.006 0.010 0.150 0.215 1.112 1.360
2007 22 0.008 0.039 0.163 0.248 1.110 1.370
2008 23 0.010 0.018 0.170 0.230 1.066 1.400
Change in Percentile Value Over Time2   - - - - 0.051 -

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 4b) Bay of Plenty Region calculated percentiles and maximum values for ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 44 0.001 0.002 0.015 0.148 0.59 3.3
1996 48 0.001 0.003 0.019 0.171 1.15 4.8
1997 53 0.000 0.002 0.010 0.125 1.07 4.3
1998 52 0.000 0.002 0.017 0.148 1.18 3.5
1999 12 0.000 0.000 0.010 0.261 1.21 1.5
2000 12 0.000 0.000 0.011 0.020 1.07 1.1
2001 12 0.000 0.000 0.000 0.020 1.10 1.1
2002 28 0.000 0.002 0.020 0.158 1.81 3.5
2003 15 0.000 0.002 0.020 0.270 1.10 1.2
2004 49 0.001 0.011 0.024 0.146 0.97 3.3
2005 47 0.009 0.016 0.034 0.130 0.77 1.6
2006 47 0.000 0.001 0.009 0.150 1.21 3.1
2007 38 0.000 0.002 0.020 0.120 1.06 3.6
2008 41 0.000 0.001 0.016 0.133 1.01 3.4
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 4c) Canterbury Region calculated percentiles and maximum values for ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 114 0.000 0.000 0.000 0.000 0.09 8.0
1996 133 0.005 0.006 0.007 0.010 0.11 8.2
1997 143 0.003 0.006 0.009 0.014 0.08 6.0
1998 153 0.003 0.005 0.009 0.014 0.07 4.0
1999 172 0.000 0.001 0.005 0.009 0.08 8.0
2000 185 0.002 0.005 0.008 0.013 0.08 11.0
2001 184 0.002 0.005 0.007 0.013 0.04 4.1
2002 186 0.004 0.006 0.010 0.016 0.04 3.5
2003 183 0.003 0.007 0.010 0.018 0.09 1.7
2004 179 0.003 0.007 0.012 0.018 0.12 0.7
2005 197 0.005 0.010 0.017 0.024 0.13 3.3
2006 199 0.003 0.008 0.012 0.022 0.13 9.4
2007 198 0.005 0.010 0.017 0.024 0.12 16.0
2008 207 0.003 0.008 0.015 0.022 0.11 14.0
Change in Percentile Value Over Time2   - 0.000 0.001 0.001 - -

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 ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 16 0.009 0.030 0.105 0.525 2.31 3.3
1996 6 0.007 0.014 0.030 0.305 0.43 0.5
1997 39 0.006 0.012 0.060 0.445 3.81 11.0
1998 43 0.004 0.015 0.054 0.493 3.69 10.4
1999 42 0.004 0.026 0.097 0.531 3.32 12.0
2000 41 0.003 0.012 0.082 0.545 3.62 11.0
2001 43 0.003 0.011 0.099 0.570 3.42 10.9
2002 38 0.001 0.011 0.080 0.524 3.49 11.1
2003 43 0.004 0.020 0.090 0.510 3.51 9.4
2004 41 0.003 0.010 0.115 0.605 3.78 9.9
2005 42 0.003 0.015 0.165 0.599 3.51 11.0
2006 43 0.002 0.011 0.095 0.533 3.57 11.1
2007 43 0.002 0.010 0.140 0.588 3.50 11.0
2008 43 0.003 0.019 0.110 0.485 3.58 11.0
Change in Percentile Value Over Time2   -0.0004 - 0.006 - - -

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 ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 3 0.014 0.020 0.218 0.28 2.36 2.9
1996 3 0.014 0.021 0.150 0.34 2.64 3.2
1997 3 0.004 0.020 0.150 0.32 2.44 3.0
1998 9 0.050 0.190 0.790 2.70 4.58 17.5
1999 13 0.020 0.050 0.335 1.70 5.04 16.5
2000 11 0.007 0.030 0.115 0.95 3.71 19.0
2001 11 0.015 0.038 0.240 1.58 4.10 19.5
2002 12 0.041 0.118 0.213 1.30 3.18 4.6
2003 8 0.070 0.140 0.250 1.68 3.20 4.3
2004 8 0.030 0.105 0.290 1.88 6.85 8.8
2005 5 0.042 0.068 0.180 1.70 3.63 4.5
2006 0
2007 4 0.049 0.113 0.920 1.82 3.65 4.2
2008 2 0.040 0.169 0.330 1.62 2.64 2.9
Change in Percentile Value Over Time2   0.003 0.008 - 0.106 - -

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 ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0
1996 1 0.025 0.025 0.025 0.025 0.03 0.0
1997 3 0.000 0.001 0.005 0.090 0.35 0.4
1998 4 0.007 0.009 0.012 0.018 0.02 0.0
1999 6 0.000 0.000 0.001 0.028 0.18 0.2
2000 3 0.010 0.010 0.010 0.010 0.01 0.0
2001 5 0.000 0.000 0.000 0.013 0.14 0.2
2002 8 0.000 0.000 0.000 0.041 0.81 1.0
2003 12 0.000 0.000 0.000 0.010 0.75 1.0
2004 10 0.000 0.000 0.001 0.020 0.39 0.7
2005 17 0.000 0.000 0.000 0.009 0.18 0.7
2006 16 0.001 0.005 0.006 0.057 0.34 1.5
2007 15 0.000 0.000 0.002 0.010 0.13 0.4
2008 17 0.000 0.000 0.006 0.025 0.29 0.4
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 3h) Northland Region calculated percentiles and maximum values for ammoniacal-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 0.020 0.022 0.025 0.038 0.07 0.1
1997 4 0.016 0.019 0.019 0.020 0.02 0.0
1998 5 0.000 0.001 0.004 0.019 0.05 0.1
1999 5 0.005 0.008 0.015 0.037 0.06 0.1
2000 6 0.001 0.002 0.004 0.030 0.10 0.1
2001 6 0.000 0.000 0.003 0.045 0.68 1.1
2002 11 0.003 0.020 0.050 0.090 1.50 2.3
2003 20 0.001 0.002 0.030 0.143 2.20 5.4
2004 29 0.000 0.001 0.014 0.085 0.68 5.0
2005 28 0.000 0.002 0.030 0.090 0.69 5.2
2006 25 0.000 0.002 0.030 0.095 0.94 5.8
2007 28 0.001 0.004 0.020 0.090 0.91 5.4
2008 27 0.000 0.001 0.015 0.070 0.63 5.8
Change in Percentile Value Over Time2   -0.0005 - - 0.006 0.08 0.58

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 ammoniacal-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 0.011 0.014 0.020 0.03 0.3
1996 20 0.009 0.009 0.010 0.016 0.03 0.1
1997 41 0.002 0.006 0.010 0.017 0.29 0.8
1998 70 0.002 0.009 0.014 0.029 0.61 2.9
1999 68 0.002 0.006 0.014 0.038 0.57 2.2
2000 75 0.002 0.007 0.014 0.030 0.48 2.6
2001 78 0.000 0.000 0.003 0.020 0.50 2.1
2002 75 0.000 0.001 0.010 0.030 0.83 18.0
2003 78 0.000 0.001 0.010 0.040 0.72 2.6
2004 72 0.000 0.001 0.010 0.048 1.07 9.9
2005 71 0.000 0.001 0.010 0.040 1.56 3.7
2006 72 0.000 0.000 0.001 0.020 0.68 2.5
2007 64 0.000 0.000 0.000 0.020 0.82 2.8
2008 60 0.000 0.000 0.003 0.040 0.92 3.2
Change in Percentile Value Over Time2   -0.0003 -0.001 -0.001 0.001 0.07 0.2

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 ammoniacal-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 9.7E-04 1.9E-03 0.007 0.018 0.037 0.05
1999 4 1.1E-02 1.8E-02 0.020 0.033 0.043 0.05
2000 15 3.7E-08 9.0E-07 0.000 0.008 0.056 0.78
2001 15 9.3E-11 7.6E-09 0.000 0.000 0.033 0.08
2002 20 1.2E-09 5.4E-08 0.000 0.001 0.045 0.10
2003 24 7.5E-03 9.5E-03 0.012 0.016 0.047 0.26
2004 18 7.0E-03 1.0E-02 0.011 0.013 0.029 0.08
2005 23 6.9E-04 1.1E-03 0.002 0.010 0.031 0.08
2006 21 4.0E-05 4.3E-04 0.005 0.012 0.064 0.61
2007 22 4.8E-05 3.4E-04 0.005 0.015 0.098 0.98
2008 26 1.4E-04 6.2E-04 0.010 0.014 0.096 5.30
Change in Percentile Value Over Time2   - - - - - 0.08

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 ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 10 0.005 0.020 0.120 0.96 52.6 79.2
1996 13 0.006 0.020 0.255 1.26 6.8 85.8
1997 13 0.005 0.030 0.090 1.07 9.2 97.5
1998 12 0.007 0.016 0.058 0.84 14.9 106.8
1999 12 0.000 0.002 0.070 0.56 62.9 184.0
2000 10 0.006 0.042 0.265 3.34 50.8 84.9
2001 29 0.004 0.017 0.128 2.02 31.9 64.3
2002 37 0.001 0.006 0.025 0.64 27.6 209.0
2003 14 0.001 0.010 0.464 1.30 29.7 5000.0
2004 20 0.001 0.018 0.435 1.29 36.0 527.3
2005 25 0.000 0.005 0.115 1.25 11.3 28.9
2006 39 0.000 0.001 0.010 0.41 5.8 201.0
2007 39 0.000 0.005 0.021 1.17 4.6 33.7
2008 25 0.001 0.006 0.023 0.78 4.7 11.3
Change in Percentile Value Over Time2   -0.0005 -0.001 - - - -

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 ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 0            
1996 10 0.003 0.005 0.013 0.021 0.043 0.056
1997 10 0.004 0.006 0.015 0.020 0.047 0.070
1998 9 0.000 0.000 0.000 0.020 0.226 0.310
1999 10 0.003 0.005 0.011 0.028 0.042 0.050
2000 10 0.002 0.004 0.014 0.020 0.063 0.070
2001 10 0.000 0.001 0.002 0.010 0.031 0.040
2002 13 0.005 0.008 0.010 0.020 0.092 0.140
2003 16 0.006 0.008 0.015 0.020 0.041 0.065
2004 16 0.001 0.003 0.006 0.016 0.036 0.065
2005 16 0.001 0.003 0.007 0.020 0.050 0.055
2006 16 0.000 0.001 0.006 0.010 0.031 0.055
2007 16 0.001 0.005 0.008 0.016 0.038 0.060
2008 16 0.004 0.006 0.015 0.026 0.073 0.080
Change in Percentile Value Over Time2   - - - - - -

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

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 1 0.110 0.110 0.110 0.110 0.11 0.1
1996 2 0.010 0.010 0.020 0.033 0.04 0.0
1997 5 0.000 0.000 0.001 0.004 0.03 0.0
1998 5 0.020 0.020 0.020 0.020 0.02 0.0
1999 6 0.000 0.000 0.002 0.090 0.84 1.5
2000 5 0.090 0.090 0.090 0.090 0.09 0.1
2001 10 0.000 0.000 0.004 0.034 0.10 0.4
2002 37 0.001 0.003 0.010 0.020 0.12 1.6
2003 34 0.001 0.005 0.010 0.022 0.06 0.5
2004 60 0.000 0.000 0.003 0.010 0.05 1.6
2005 30 0.000 0.000 0.002 0.020 0.14 0.5
2006 65 0.000 0.000 0.007 0.020 0.07 1.6
2007 63 0.000 0.000 0.006 0.020 0.10 20.0
2008 66 0.000 0.000 0.004 0.016 0.16 1.5
Change in Percentile Value Over Time2   - - - -0.003 - -

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 ammoniacal-nitrogen in groundwater (in mg/L), based on site-specific median values.

Year n1 Percentile Max
5th 25th 50th 75th 95th
1995 10 0.0500 0.050 0.050 0.086 0.24 0.29
1996 23 0.0080 0.018 0.050 0.050 0.25 0.34
1997 29 0.0006 0.002 0.010 0.050 0.22 0.30
1998 47 0.0006 0.005 0.050 0.340 3.47 9.63
1999 47 0.0006 0.003 0.050 0.354 3.08 9.07
2000 53 0.0002 0.001 0.020 0.280 2.47 8.48
2001 48 0.0005 0.003 0.050 0.303 2.74 9.00
2002 48 0.0011 0.010 0.050 0.349 2.88 9.95
2003 49 0.0014 0.009 0.050 0.316 2.59 9.58
2004 63 0.0013 0.010 0.030 0.195 3.45 9.70
2005 71 0.0008 0.010 0.020 0.163 2.37 10.20
2006 70 0.0001 0.001 0.020 0.101 2.56 10.70
2007 69 0.0001 0.001 0.017 0.140 2.55 11.10
2008 69 0.0001 0.001 0.018 0.150 2.46 10.70
Change in Percentile Value Over Time2   -0.0001 - -0.002 - - 0.370

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 ammoniacal-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 0.010 0.010 0.010 0.010 0.01 0.01
1999 7 0.030 0.030 0.030 0.030 0.03 0.03
2000 7 0.005 0.009 0.010 0.015 0.05 0.07
2001 7 0.000 0.000 0.020 0.058 1.95 2.74
2002 6 0.000 0.000 0.001 0.019 0.08 0.10
2003 7 0.000 0.000 0.001 0.006 0.02 0.02
2004 8 0.003 0.005 0.009 0.030 0.03 0.03
2005 8 0.008 0.018 0.025 0.055 0.07 0.07
2006 8 0.001 0.003 0.013 0.035 0.08 0.10
2007 8 0.000 0.000 0.001 0.004 0.02 0.02
2008 8 0.000 0.000 0.001 0.010 0.04 0.05
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.