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Figure 1. National and regional summary statistics for state and trends in key indicators of groundwater quality based on all data collected from 1995 to 2008 (cf. Section 2.2).

Numbers above X axes show the number of sites at which state and trend statistics could be calculated for the parameter in question for the region of interest. Colour coding for box-whisker plots shows national-level statistics (blue) or regional-level statistics (red).

Figure 1. National and regional summary statistics

(Figure 1a)Upper graph. Percentage of New Zealand monitoring sites at which median concentrations calculated for the entire period from 1995 to 2008 exceed water quality guidelines for nitrate-nitrogen.
Council n1 DWSNZ ANZECC
GV2 = 11.3 mg/L TV3 = 7.2 mg/L
# Sites Exceeding % Sites Exceeding4 # Sites Exceeding % Sites Exceeding4
Auckland 24 0 0.0 1 4.2
Bay of Plenty 54 0 0.0 0 0.0
Canterbury 279 14 5.0 46 16.5
Gisborne 0        
Hawkes Bay 45 0 0.0 0 0.0
Manawatu-Wanganui 24 3 12.5 4 16.7
Marlborough 24 0 0.0 1 4.2
Northland 39 0 0.0 5 12.8
Otago 98 4 4.1 7 7.1
Southland 52 1 1.9 7 13.5
Taranaki 71 5 7.0 8 11.3
Tasman 16 2 12.5 2 12.5
Waikato 115 15 13.0 33 28.7
Wellington 71 0 0.0 7 9.9
West Coast 8 0 0.0 0 0.0
All 920 44 4.8 121 13.2

1 Number of sites where median could be calculated (i.e. there was at least one sample result from that site within the time period of interest).

2 Aesthetic Guideline Value specified in DWSNZ 2005.

3 Trigger Value for toxicity and/or ecosystem protection (95% level) specified in ANZECC 2000.

4 Percentage of monitoring sites at which median exceeds the water quality standard, relative to the total number of sites for which a median could be calculated for the parameter in question within the time period of interest.

(Figure 1a) Lower graph. Percentiles by region for nitrate-nitrogen for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 24 0.001 0.001 0.003 0.071 5.758
Bay of Plenty 54 0.001 0.005 0.068 0.370 3.327
Canterbury 279 0.100 1.100 3.400 6.150 11.455
Gisborne 0          
Hawkes Bay 45 0.002 0.005 0.015 0.190 4.460
Manawatu-Wanganui 24 0.003 0.070 0.115 0.741 12.850
Marlborough 24 0.002 0.088 0.633 1.724 5.679
Northland 39 0.001 0.008 0.168 3.770 8.581
Otago 98 0.004 0.061 0.665 2.890 8.073
Southland 52 0.005 1.375 3.400 5.420 9.945
Taranaki 71 0.002 1.243 2.065 4.335 11.700
Tasman 16 0.007 0.288 1.725 4.125 14.250
Waikato 115 0.084 1.680 4.160 7.985 15.575
Wellington 71 0.000 0.002 0.515 3.273 10.069
West Coast 8 0.350 0.885 1.075 2.300 3.590
All 920 0.000 0.100 1.700 4.700 11.000

(Figure 1b) Upper graph. Total number of monitoring sites (n) at which site-specific trend tests for nitrate-nitrogen could be performed for the time period 1995 to 2008 (i.e. the parameter had been measured at least three times between 1995 and 2008). Also shown are the number and percentage of sites at which significant increasing or decreasing trends were detected (INCR or DECR, respectively) and the number of sites at which no significant trend was detected (N).

Region n INCR DECR N %INCR %DECR %N
Auckland 21.0 3.0 6.0 12.0 14.3 28.6 57.1
Bay of Plenty 53.0 3.0 4.0 46.0 5.7 7.5 86.8
Canterbury 272.0 81.0 16.0 175.0 29.8 5.9 64.3
Hawke's Bay 45.0 8.0 4.0 33.0 17.8 8.9 73.3
Manawatu 21.0 2.0 4.0 15.0 9.5 19.0 71.4
Marlborough 23.0 5.0 2.0 16.0 21.7 8.7 69.6
Northland 37.0 3.0 3.0 31.0 8.1 8.1 83.8
Otago 98.0 12.0 11.0 75.0 12.2 11.2 76.5
Southland 41.0 8.0 5.0 28.0 19.5 12.2 68.3
Taranaki 70.0 5.0 9.0 56.0 7.1 12.9 80.0
Tasman 16.0 4.0 3.0 9.0 25.0 18.8 56.3
Waikato 110.0 36.0 22.0 52.0 32.7 20.0 47.3
Wellington 71.0 4.0 14.0 53.0 5.6 19.7 74.6
West Coast 8.0 4.0 0.0 4.0 50.0 0.0 50.0

(Figure1b) Lower graph. Percentiles by region for trends in nitrate-nitrogen for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 21 -0.001 0.000 0.000 0.066 0.432
Bay of Plenty 53 -0.502 -0.050 -0.001 0.240 0.299
Canterbury 272 -0.174 0.015 0.103 0.242 0.620
Gisborne 0          
Hawkes Bay 45 -0.014 -0.002 0.007 0.037 0.154
Manawatu-Wanganui 21 -0.332 -0.227 0.000 0.006 0.010
Marlborough 23 -0.015 0.001 0.077 0.311 0.752
Northland 37 -0.613 -0.020 0.002 0.191 0.384
Otago 98 -0.289 -0.064 0.003 0.091 0.275
Southland 41 -0.227 -0.100 0.093 0.286 0.378
Taranaki 70 -0.511 -0.075 -0.011 0.223 1.000
Tasman 16 -0.433 -0.162 0.005 0.286 0.431
Waikato 110 -0.682 -0.161 0.041 0.245 0.971
Wellington 71 -0.435 -0.286 -0.072 0.000 0.084
West Coast 8 0.012 0.042 0.120 0.326 0.667
All 886 -0.423 -0.042 0.029 0.203 0.749

Figure 1. National and regional summary statistics

(Figure 1c) Upper graph. Percentage of New Zealand monitoring sites at which median concentrations calculated for the entire period from 1995 to 2008 exceed water quality guidelines for ammoniacal nitrogen.

Council n1 DWSNZ ANZECC
GV2 = 1.5 mg/L TV3 = 0.9 mg/L
# Sites Exceeding % Sites Exceeding4 # Sites Exceeding % Sites Exceeding4
Auckland 24 0 0.0 2 8.3
Bay of Plenty 54 1 1.9 4 7.4
Canterbury 279 3 1.1 4 1.4
Gisborne 0        
Hawkes Bay 45 7 15.6 8 17.8
Manawatu-Wanganui 27 8 29.6 9 33.3
Marlborough 23 0 0.0 0 0.0
Northland 40 1 2.5 2 5.0
Otago 98 3 3.1 4 4.1
Southland 47 0 0.0 0 0.0
Taranaki 71 3 4.2 4 5.6
Tasman 16 0 0.0 0 0.0
Waikato 115 1 0.9 1 0.9
Wellington 71 6 8.5 9 12.7
West Coast 8 0 0.0 0 0.0
All 918 35 3.8 49 5.3

1 Number of sites where median could be calculated (i.e. there was at least one sample result from that site within the time period of interest).

2 Aesthetic Guideline Value specified in DWSNZ 2005.

3 Trigger Value for toxicity and/or ecosystem protection (95% level) specified in ANZECC 2000.

4 Percentage of monitoring sites at which median exceeds the water quality standard, relative to the total number of sites for which a median could be calculated for the parameter in question within the time period of interest.

(Figure 1c) Lower graph. Percentiles by region for ammoniacal nitrogen for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 24 0.001 0.009 0.145 0.290 1.201
Bay of Plenty 54 0.000 0.002 0.020 0.152 1.008
Canterbury 279 0.004 0.006 0.008 0.011 0.069
Gisborne 0          
Hawkes Bay 45 0.000 0.007 0.089 0.570 3.391
Manawatu-Wanganui 27 0.013 0.030 0.250 1.850 4.260
Marlborough 23 0.000 0.000 0.005 0.010 0.152
Northland 40 0.000 0.000 0.020 0.085 0.726
Otago 98 0.002 0.005 0.010 0.024 0.667
Southland 47 0.000 0.001 0.005 0.013 0.045
Taranaki 71 0.001 0.013 0.102 1.120 5.270
Tasman 16 0.000 0.001 0.004 0.009 0.040
Waikato 115 0.000 0.002 0.010 0.070 6.080
Wellington 71 0.000 0.001 0.020 0.290 4.860
West Coast 8 0.000 0.000 0.000 0.003 0.021
All 918 0.000 0.001 0.010 0.030 0.970

(Figure 1d) Upper graph. Total number of monitoring sites (n) at which site-specific trend tests for ammoniacal-nitrogen could be performed for the time period 1995 to 2008 (i.e. the parameter had been measured at least three times between 1995 and 2008).

Region n INCR DECR N %INCR %DECR %N
Auckland 22.0 0.0 4.0 18.0 0.0 18.2 81.8
Bay of Plenty 53.0 6.0 3.0 44.0 11.3 5.7 83.0
Canterbury 275.0 72.0 4.0 199.0 26.2 1.5 72.4
Hawke's Bay 45.0 2.0 10.0 33.0 4.4 22.2 73.3
Manawatu 25.0 3.0 1.0 21.0 12.0 4.0 84.0
Marlborough 19.0 1.0 0.0 18.0 5.3 0.0 94.7
Northland 38.0 0.0 4.0 34.0 0.0 10.5 89.5
Otago 89.0 7.0 8.0 74.0 7.9 9.0 83.1
Southland 36.0 0.0 0.0 36.0 0.0 0.0 100.0
Taranaki 70.0 5.0 12.0 53.0 7.1 17.1 75.7
Tasman 15.0 1.0 0.0 14.0 6.7 0.0 93.3
Waikato 82.0 4.0 4.0 74.0 4.9 4.9 90.2
Wellington 67.0 9.0 15.0 43.0 13.4 22.4 64.2
West Coast 8.0 0.0 0.0 8.0 0.0 0.0 100.0

(Figure 1d) Lower graph. Percentiles by region for trends in ammoniacal nitrogen for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 22 -0.013 -0.008 -0.006 -0.005 -0.002
Bay of Plenty 53 -0.196 -0.017 0.000 0.003 0.025
Canterbury 275 -0.002 0.001 0.001 0.001 0.002
Gisborne 0          
Hawkes Bay 45 -0.080 -0.002 -0.001 0.000 0.004
Manawatu-Wanganui 25 -0.007 0.003 0.035 0.081 0.126
Marlborough 19 0.001 0.001 0.001 0.001 0.001
Northland 38 -0.036 -0.016 -0.006 -0.005 -0.004
Otago 89 -0.003 -0.001 0.000 0.031 0.091
Southland 36          
Taranaki 70 -0.037 -0.001 -0.001 0.004 0.026
Tasman 15 0.001 0.001 0.001 0.001 0.001
Waikato 82 -0.007 -0.002 0.002 0.021 0.029
Wellington 67 -0.021 -0.008 -0.003 0.000 0.012
West Coast 8          
All 844 -0.026 -0.002 0.001 0.001 0.031

Figure 1. National and regional summary statistics

(Figure 1e) Upper graph. Percentage of New Zealand monitoring sites at which median concentrations calculated for the entire period from 1995 to 2008 exceed water quality guidelines for E. coli.

Council n1 DWSNZ ANZECC
 MAV2= 1 cfu/100 ml TV3 = 100 cfu/100 ml
# Sites Exceeding % Sites Exceeding4 # Sites Exceeding % Sites Exceeding4
Auckland 21 7 33.3 2 9.5
Bay of Plenty5 20 0 0.0 0 0.0
Canterbury 272 42 15.4 2 0.7
Gisborne 0        
Hawkes Bay 35 5 14.3 2 5.7
Manawatu-Wanganui 0        
Marlborough 9 1 11.1 0 0.0
Northland 40 10 25.0 0 0.0
Otago 62 19 30.6 2 3.2
Southland 43 3 7.0 1 2.3
Taranaki 67 47 70.1 6 9.0
Tasman 0        
Waikato 64 16 25.0 1 1.6
Wellington 60 11 18.3 1 1.7
West Coast 8 1 12.5 0 0.0
All 701 162 23.1 17 2.4

1 Number of sites where median could be calculated (i.e. there was at least one sample result from that site within the time period of interest).

2 Health-related Maximum Allowable Value specified in DWSNZ 2005.

3 Trigger Value for stock drinking water specified in ANZECC 2000.

4 Percentage of monitoring sites at which median exceeds the water quality standard, relative to the total number of sites for which a median could be calculated for the parameter in question within the time period of interest.

5 Faecal coliforms used as a proxy for E. coli. Note that E. coli is the only parameter that is considered in DWSNZ 2005.

(Figure 1e) Lower graph. Percentiles by region for E. coli for period 1995-2008

Council n Percentiles
    5th  25th 50th 75th 95th
Auckland 21 9.2E-06 3.8E-04 1.5E-02 2.0E+00 1.5E+02
Bay of Plenty 20 5.0E-02 6.6E-01 1.0E+00 1.5E+00 8.1E+00
Canterbury 272 4.7E-03 4.6E-02 7.1E-01 2.7E+00 2.1E+01
Gisborne 0          
Hawkes Bay 35 1.7E-16 1.5E-12 5.7E-07 5.0E-01 8.1E+00
Manawatu-Wanganui 0          
Marlborough 9 9.5E-02 1.3E-01 5.5E-01 1.0E+00 6.0E+00
Northland 40 2.8E-13 1.4E-07 3.1E-01 1.1E+00 1.0E+01
Otago 62 7.0E-06 3.8E-04 1.9E-02 2.0E+00 2.1E+01
Southland 43 1.0E-03 4.6E-03 5.7E-02 1.0E+00 7.2E+00
Taranaki 67 1.9E-01 1.0E+00 5.0E+00 1.6E+01 1.6E+02
Tasman 0          
Waikato 64 1.8E-04 2.4E-03 4.9E-02 1.1E+00 1.2E+01
Wellington 60 5.3E-02 5.6E-01 1.5E+00 5.5E+00 2.5E+01
West Coast 8 1.2E-01 1.5E-01 4.8E-01 7.9E-01 3.6E+00
All 701 1.0E-08 1.0E-06 5.0E-04 1.0E+00 2.2E+01

(Figure 1f) Upper graph. Total number of monitoring sites (n) at which site-specific trend tests for E.coli could be performed for the time period 1995 to 2008 (i.e. the parameter had been measured at least three times between 1995 and 2008).

Region n INCR DECR N %INCR %DECR %N
Auckland 7.0 0.0 0.0 7.0 0.0 0.0 100.0
Bay of Plenty 12.0 0.0 0.0 12.0 0.0 0.0 100.0
Canterbury 152.0 2.0 2.0 148.0 1.3 1.3 97.4
Hawke's Bay 12.0 0.0 0.0 12.0 0.0 0.0 100.0
Manawatu 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Marlborough 3.0 0.0 0.0 3.0 0.0 0.0 100.0
Northland 31.0 0.0 1.0 30.0 0.0 3.2 96.8
Otago 29.0 0.0 1.0 28.0 0.0 3.4 96.6
Southland 30.0 0.0 0.0 30.0 0.0 0.0 100.0
Taranaki 54.0 0.0 0.0 54.0 0.0 0.0 100.0
Tasman 0.0 0.0 0.0 0.0 0.0 0.0 0.0
Waikato 20.0 0.0 0.0 20.0 0.0 0.0 100.0
Wellington 21.0 1.0 0.0 20.0 4.8 0.0 95.2
West Coast 8.0 0.0 0.0 8.0 0.0 0.0 100.0

(Figure 1f) Lower graph. Percentiles by region for trends in E.coli for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 7          
Bay of Plenty 12          
Canterbury 152 -1.341 -0.563 0.043 0.684 1.548
Gisborne 0          
Hawkes Bay 12          
Manawatu-Wanganui 0          
Marlborough 3          
Northland 31 -1.398 -1.398 -1.398 -1.398 -1.398
Otago 29 -37.029 -37.029 -37.029 -37.029 -37.029
Southland 30          
Taranaki 54          
Tasman 0          
Waikato 20          
Wellington 21 4.161 4.161 4.161 4.161 4.161
West Coast 8          
All 367 -26.381 -1.467 -0.238 1.044 3.442

Figure 1. National and regional summary statistics

(Figure 1g) Upper graph. Percentage of New Zealand monitoring sites at which median concentrations calculated for the entire period from 1995 to 2008 exceed water quality guidelines for iron.

Council n1 DWSNZ
 GV2 = 0.2 mg/L
# Sites Exceeding % Sites Exceeding3
Auckland 23 6 26.1
Bay of Plenty 54 26 48.1
Canterbury 268 21 7.8
Gisborne 0    
Hawkes Bay 45 17 37.8
Manawatu-Wanganui 27 14 51.9
Marlborough 24 3 12.5
Northland 39 14 35.9
Otago 80 14 17.5
Southland 39 4 10.3
Taranaki 7 1 14.3
Tasman 16 4 25.0
Waikato 110 12 10.9
Wellington 62 29 46.8
West Coast 8 1 12.5
All 802 171 21.3

1 Number of sites where median could be calculated (i.e. there was at least one sample result from that site within the time period of interest).

2 Aesthetic Guideline Value specified DWSNZ 2005

3 Percentage of monitoring sites at which median exceeds the water quality standard, relative to the total number of sites for which a median could be calculated for the parameter in question within the time period of interest.

(Figure 1g) Lower graph. Percentiles by region for iron for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 23 0.000 0.005 0.014 0.185 4.679
Bay of Plenty 54 0.001 0.016 0.102 1.621 9.207
Canterbury 268 0.004 0.019 0.040 0.065 0.235
Gisborne 0          
Hawkes Bay 45 0.001 0.020 0.160 0.795 8.928
Manawatu-Wanganui 27 0.045 0.070 0.360 2.300 30.500
Marlborough 24 0.001 0.007 0.012 0.023 0.474
Northland 39 0.000 0.004 0.050 0.975 9.744
Otago 80 0.000 0.005 0.019 0.066 1.500
Southland 39 0.001 0.003 0.004 0.014 6.140
Taranaki 7 0.001 0.016 0.030 0.105 2.028
Tasman 16 0.000 0.001 0.009 0.206 2.575
Waikato 110 0.000 0.000 0.000 0.019 0.719
Wellington 62 0.000 0.023 0.130 2.164 7.955
West Coast 8 0.005 0.009 0.039 0.101 0.226
All 802 0.000 0.010 0.030 0.120 4.480

(Figure 1h) Upper graph. Total number of monitoring sites (n) at which site-specific trend tests for iron could be performed for the time period 1995 to 2008 (i.e. the parameter had been measured at least three times between 1995 and 2008).

Region n INCR DECR N %INCR %DECR %N
Auckland 23.0 9.0 0.0 14.0 39.1 0.0 60.9
Bay of Plenty 44.0 7.0 1.0 36.0 15.9 2.3 81.8
Canterbury 224.0 2.0 8.0 214.0 0.9 3.6 95.5
Hawke's Bay 45.0 2.0 21.0 22.0 4.4 46.7 48.9
Manawatu 26.0 1.0 9.0 16.0 3.8 34.6 61.5
Marlborough 21.0 0.0 2.0 19.0 0.0 9.5 90.5
Northland 33.0 0.0 2.0 31.0 0.0 6.1 93.9
Otago 58.0 1.0 0.0 57.0 1.7 0.0 98.3
Southland 35.0 5.0 4.0 26.0 14.3 11.4 74.3
Taranaki 7.0 0.0 1.0 6.0 0.0 14.3 85.7
Tasman 15.0 1.0 2.0 12.0 6.7 13.3 80.0
Waikato 23.0 1.0 2.0 20.0 4.3 8.7 87.0
Wellington 46.0 0.0 8.0 38.0 0.0 17.4 82.6
West Coast 7.0 0.0 1.0 6.0 0.0 14.3 85.7

(Figure 1h) Lower graph. Percentiles by region for trends in iron for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 23 0.001 0.003 0.052 0.119 0.160
Bay of Plenty 44 0.001 0.025 0.046 0.398 0.558
Canterbury 224 -0.149 -0.025 -0.013 -0.009 0.057
Gisborne 0          
Hawkes Bay 45 -0.109 -0.049 -0.008 -0.003 0.193
Manawatu-Wanganui 26 -0.452 -0.056 -0.025 -0.008 0.024
Marlborough 21 -0.003 -0.003 -0.003 -0.003 -0.003
Northland 33 -0.010 -0.008 -0.006 -0.004 -0.002
Otago 58 0.009 0.009 0.009 0.009 0.009
Southland 35 -0.251 -0.007 0.001 0.002 0.002
Taranaki 7 -0.003 -0.003 -0.003 -0.003 -0.003
Tasman 15 -0.083 -0.049 -0.006 0.215 0.393
Waikato 23 -0.200 -0.136 -0.046 -0.021 -0.001
Wellington 46 -0.129 -0.025 -0.011 -0.004 -0.002
West Coast 7 -0.060 -0.060 -0.060 -0.060 -0.060
All 597 -0.212 -0.024 -0.005 0.003 0.389

Figure 1. National and regional summary statistics

(Figure 1i) Upper graph. Percentage of New Zealand monitoring sites at which median concentrations calculated for the entire period from 1995 to 2008 exceed water quality guidelines for manganese.

Council n1 DWSNZ DWSNZ ANZECC
GV2 = 0.04 mg/L  MAV3 = 0.4 mg/L TV4 = 1.9 mg/L
# Sites Exceeding % Sites Exceeding5 # Sites Exceeding % Sites Exceeding5 # Sites Exceeding % Sites Exceeding5
Auckland 24 8 33.3 0 0.0 0 0.0
Bay of Plenty 54 26 48.1 13 24.1 4 7.4
Canterbury 268 29 10.8 8 3.0 2 0.7
Gisborne 0            
Hawkes Bay 45 24 53.3 8 17.8 0 0.0
Manawatu-Wanganui 27 20 74.1 11 40.7 1 3.7
Marlborough 24 5 20.8 0 0.0 0 0.0
Northland 39 16 41.0 6 15.4 1 2.6
Otago 61 18 29.5 5 8.2 1 1.6
Southland 39 5 12.8 2 5.1 0 0.0
Taranaki 4 3 75.0 3 75.0 0 0.0
Tasman 16 3 18.8 1 6.3 1 6.3
Waikato 113 19 16.8 3 2.7 1 0.9
Wellington 62 29 46.8 15 24.2 0 0.0
West Coast 8 1 12.5 0 0.0 0 0.0
All 784 211 26.9 78 9.9 11 1.4

1 Number of sites where median could be calculated (i.e. there was at least one sample result from that site within the time period of interest).

2 Aesthetic Guideline Value specified in DWSNZ 2005.

3 Health-related Maximum Allowable Value specified in DWSNZ 2005.

4 Trigger Value for ecosystem protection (95% level) specified in ANZECC 2000.

5 Percentage of monitoring sites at which median exceeds the water quality standard, relative to the total number of sites for which a median could be calculated for the parameter in question within the time period of interest.

(Figure 1i) Lower graph. Percentiles by region for manganese for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 24 0.000 0.002 0.018 0.058 0.169
Bay of Plenty 54 0.000 0.002 0.027 0.374 3.751
Canterbury 268 0.005 0.008 0.010 0.017 0.164
Gisborne 0          
Hawkes Bay 45 0.000 0.006 0.046 0.210 0.616
Manawatu-Wanganui 27 0.001 0.032 0.270 0.725 1.185
Marlborough 24 0.000 0.000 0.002 0.016 0.077
Northland 39 0.000 0.002 0.025 0.215 1.439
Otago 61 0.000 0.001 0.010 0.058 0.490
Southland 39 0.000 0.000 0.001 0.004 0.366
Taranaki 4 0.002 0.006 0.009 0.257 0.661
Tasman 16 0.000 0.000 0.001 0.017 0.890
Waikato 113 0.000 0.001 0.002 0.009 0.226
Wellington 62 0.000 0.000 0.019 0.350 1.123
West Coast 8 0.000 0.001 0.007 0.030 0.112
All 784 0.000 0.000 0.010 0.050 0.850

(Figure 1j) Upper graph. Total number of monitoring sites (n) at which site-specific trend tests for manganese could be performed for the time period 1995 to 2008 (i.e. the parameter had been measured at least three times between 1995 and 2008).

Region n INCR DECR N %INCR %DECR %N
Auckland 24.0 8.0 2.0 14.0 33.3 8.3 58.3
Bay of Plenty 50.0 3.0 4.0 43.0 6.0 8.0 86.0
Canterbury 118.0 0.0 3.0 115.0 0.0 2.5 97.5
Hawke's Bay 44.0 6.0 12.0 26.0 13.6 27.3 59.1
Manawatu 21.0 2.0 7.0 12.0 9.5 33.3 57.1
Marlborough 19.0 5.0 1.0 13.0 26.3 5.3 68.4
Northland 39.0 3.0 6.0 30.0 7.7 15.4 76.9
Otago 29.0 0.0 0.0 29.0 0.0 0.0 100.0
Southland 29.0 2.0 5.0 22.0 6.9 17.2 75.9
Taranaki 6.0 0.0 3.0 3.0 0.0 50.0 50.0
Tasman 12.0 2.0 1.0 9.0 16.7 8.3 75.0
Waikato 85.0 0.0 1.0 84.0 0.0 1.2 98.8
Wellington 38.0 3.0 5.0 30.0 7.9 13.2 78.9
West Coast 7.0 2.0 0.0 5.0 28.6 0.0 71.4

(Figure 1j) Lower graph. Percentiles by region for trends in manganese for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 24.000 0.000 0.000 0.001 0.001 0.005
Bay of Plenty 50.000 -0.015 -0.005 -0.003 0.000 0.010
Canterbury 118.000 -0.200 -0.123 -0.028 -0.014 -0.003
Gisborne 0.000          
Hawkes Bay 44.000 -0.003 -0.001 0.000 0.002 0.014
Manawatu-Wanganui 21.000 -0.048 -0.036 -0.005 -0.001 0.018
Marlborough 19.000 0.000 0.000 0.000 0.000 0.001
Northland 39.000 -0.164 -0.023 -0.001 0.000 0.002
Otago 29.000          
Southland 29.000 -0.012 -0.007 -0.001 0.001 0.005
Taranaki 6.000 -0.024 -0.017 -0.008 -0.004 -0.001
Tasman 12.000 -0.001 0.000 0.002 0.012 0.021
Waikato 85.000 -0.001 -0.001 -0.001 -0.001 -0.001
Wellington 38.000 -0.042 -0.024 0.000 0.001 0.006
West Coast 7.000 0.004 0.017 0.034 0.050 0.063
All 523.000 -0.047 -0.004 0.000 0.001 0.019

Figure 1. National and regional summary statistics

(Figure 1k) Percentiles by region for conductivity for period 1995-2008

Council n Percentiles (mg/L)
    5th  25th 50th 75th 95th
Auckland 23 185.415 256.075 316.000 452.375 701.500
Bay of Plenty 54 88.405 123.200 207.750 490.250 27500.000
Canterbury 278 89.400 128.000 174.000 221.000 401.000
Gisborne 0          
Hawkes Bay 44 115.225 161.200 231.950 419.613 2617.000
Manawatu-Wanganui 27 166.650 287.250 464.000 577.000 6135.000
Marlborough 22 68.125 116.913 150.725 212.813 427.175
Northland 40 146.150 398.750 519.750 660.250 4392.000
Otago 99 91.550 160.575 221.000 483.825 1490.000
Southland 47 115.050 149.750 210.000 265.000 430.450
Taranaki 71 96.250 148.000 253.000 334.250 621.250
Tasman 16 142.238 205.775 219.500 299.150 481.750
Waikato 115 75.700 128.250 197.000 260.250 393.200
Wellington 71 90.250 138.625 200.000 319.000 700.000
West Coast 8 64.800 74.500 84.500 89.625 92.475
All 915 89.000 141.500 204.000 319.500 807.000

(Figure 1l) Upper graph. Total number of monitoring sites (n) at which site-specific trend tests for electrical conductivity could be performed for the time period 1995 to 2008 (i.e. the parameter had been measured at least three times between 1995 and 2008).

Region n INCR DECR N %INCR %DECR %N
Auckland 23.0 3.0 0.0 20.0 13.0 0.0 87.0
Bay of Plenty 54.0 2.0 9.0 43.0 3.7 16.7 79.6
Canterbury 277.0 78.0 7.0 192.0 28.2 2.5 69.3
Hawke's Bay 44.0 9.0 12.0 23.0 20.5 27.3 52.3
Manawatu 27.0 2.0 8.0 17.0 7.4 29.6 63.0
Marlborough 22.0 3.0 1.0 18.0 13.6 4.5 81.8
Northland 40.0 9.0 5.0 26.0 22.5 12.5 65.0
Otago 99.0 1.0 27.0 71.0 1.0 27.3 71.7
Southland 40.0 15.0 5.0 20.0 37.5 12.5 50.0
Taranaki 71.0 6.0 15.0 50.0 8.5 21.1 70.4
Tasman 16.0 8.0 1.0 7.0 50.0 6.3 43.8
Waikato 114.0 23.0 11.0 80.0 20.2 9.6 70.2
Wellington 71.0 7.0 21.0 43.0 9.9 29.6 60.6
West Coast 8.0 1.0 0.0 7.0 12.5 0.0 87.5

(Figure 1l) Lower graph. Percentiles by region for trends in electrical conductivity for period 1995-2008

Council n Percentiles 
    5th  25th 50th 75th 95th
Auckland 23 7.684 8.332 9.141 11.961 14.217
Bay of Plenty 54 -19.406 -11.507 -2.893 -1.198 54.114
Canterbury 227 -5.014 2.674 6.309 10.034 20.172
Gisborne 0          
Hawkes Bay 44 -24.154 -2.019 -0.636 3.556 4.888
Manawatu-Wanganui 27 -42.946 -5.534 -1.998 -1.689 2.962
Marlborough 22 -3.060 0.533 6.336 11.475 13.476
Northland 40 -19.030 -9.446 7.136 13.269 68.963
Otago 99 -24.596 -9.700 -7.095 -4.527 -1.920
Southland 40 -1.795 0.691 2.629 4.098 12.037
Taranaki 71 -18.841 -9.379 -3.305 0.000 9.471
Tasman 16 -2.023 2.548 4.019 9.610 11.602
Waikato 114 -8.650 -1.809 2.133 6.427 11.243
Wellington 71 -15.152 -6.673 -3.905 -0.128 9.631
West Coast 8 9.044 9.044 9.044 9.044 9.044
All 906 -16.161 -4.439 2.014 6.628 17.376