River and stream water quality and ecology - Greater Wellington ...

More documents

Recommendations

Info

River and stream water quality and ecology in the Wellington region: State and trends 4.2.2 Results An overview of the temporal trend analysis outputs, for both raw and flowadjusted data sets that contained 30% or less censored values, is presented in Table 4.7. Full details of all other trend analysis results can be found in Appendix 7. The majority of RSoE sites were typically stable across the five-year period, based on both raw and flow-adjusted data for the 14 variables assessed. However, pH was an exception, with around half of the sites exhibiting decreasing trends over the reporting period. The reason for the declining pH trends is unclear but it should be noted that there were some changes in sampling personnel (and field meters) during the early part of the reporting period. 18 Further, along with water temperature and DO which also exhibit significant diurnal variation, changes in site sampling time during the reporting period confound interpretation of the trend results. The focus of the following sections is therefore placed on describing the meaningful trends (ie, statistically significant and with a rate of change >1% per annum) observed in water clarity, turbidity, nutrient concentrations, TOC concentrations, and E. coli bacteria counts. A total of 78 meaningful trends were identified in the raw data sets across these nine variables (equating to 14.1% out of a total of 411 possible trends), with half of these trends associated with just three variables: TP (15 sites), NNN (13 sites) and TN (11 sites). (a) Visual clarity (black disc) and turbidity Eight RSoE sites exhibited meaningful declining trends in raw black disc (visual clarity) values, three of which also exhibited these trends in flowadjusted data (Table 4.8). Rates of decline ranged from 0.06 m/year (Ngarara Stream at Field Way) to 0.31 m/year (Beef Creek at Headwaters). These eight sites comprised a mixture of hard and soft-bottomed sites and all have lowelevation sources of flow. Two of these sites are classed as reference sites (Wainuiomata River at Manuka Track and Beef Creek at Headwaters), while the remaining six sites are located in catchments dominated by pastoral (five sites) or urban landcover (one site). Only two RSoE sites (Taueru River at Castlehill and Whangaehu River 250 m from confluence) that recorded deteriorating trends in visual clarity recorded corresponding deteriorating (ie, increasing) trends in turbidity (raw data) (Table 4.9). Five sites recorded meaningful decreasing trends in turbidity which were typically only evident in flow-adjusted data (Table 4.9). 18 From July 2005 up until January 2007, monthly water sampling was undertaken by external contractors. Issues were identified with the quality of some field measurements reported during this time. WGN_DOCS-#1100598-V3 PAGE 45 OF 160
River and stream water quality and ecology in the Wellington region: State and trends Table 4.7: Summary of temporal trends in selected water quality variables for 55 RSoE sites sampled monthly between July 2006 and June 2011. Trend results are provided for both raw and flow-adjusted datasets that comprised no more than 30% of censored values Variable Significant increase (n) Meaningful increase (n) No trend (n) RAW DATA FLOW-ADJUSTED DATA Significant decrease (n) Meaningful decrease (n) Total no. sites assessed Censored sites (n) Significant increase (n) Meaningful increase (n) PAGE 46 OF 160 WGN_DOCS-#1100598-V3 No trend (n) Significant decrease (n) Meaningful decrease (n) Total no. sites assessed Water temperature Dissolved 0 2 41 0 12 55 0 0 2 32 0 10 44 0 oxygen (% sat) Dissolved 0 7 47 0 1 55 0 0 8 35 0 1 44 0 oxygen (mg/L) 0 7 47 0 1 55 0 0 7 37 0 0 44 0 pH 0 0 26 4 25 55 0 0 0 20 5 19 44 0 Conductivity 0 2 52 0 1 55 0 0 4 38 0 2 44 0 Visual clarity 0 0 47 0 8 55 0 0 0 41 0 3 44 0 Turbidity 0 2 52 0 1 55 0 0 0 39 0 5 44 0 Total organic carbon 0 6 49 0 0 55 0 0 4 43 0 1 44 0 Nitrite-nitrate nitrogen 0 0 41 0 13 54 1 0 0 34 0 9 43 1 Ammoniacal nitrogen 0 0 7 0 2 9 46 0 0 7 0 0 7 37 Total nitrogen Dissolved 0 0 32 0 11 43 12 0 0 26 0 7 33 11 reactive phosphorus 0 4 24 0 6 34 21 0 4 26 0 2 28 16 Total phosphorus 0 1 36 0 14 51 4 0 0 27 0 13 40 4 E. coli 0 7 45 0 3 55 0 0 2 39 0 5 44 0 Total 0 38 546 4 98 686 84 0 31 444 5 77 547 69 Censored sites (n)
Page 1 and 2:
River and stream water quality and
Page 3 and 4: DISCLAIMER This report has been pre
Page 5 and 6: observed trends were unclear. The p
Page 7 and 8: 5. Periphyton - state and trends 57
Page 10 and 11: River and stream water quality and
Page 14 and 15: Figure 2.1: RSoE monitoring sites a
Page 16 and 17: 2.4.2 Biological variables River an
Page 52 and 53: 4.2 Temporal trends River and strea
Page 72 and 73: TN (mg/L) Temperature ( 0 c) Shade
Page 80 and 81: Chlorophyll a (mg/m 2 ) 90 80 70 60
Page 82 and 83: 25th percentile summer time flow m
Page 90 and 91: RS06 Shade RS11 Habitat RS35 RS49 R
Page 104 and 105:
Page 106 and 107:
IBI Score 60 50 40 30 20 10 0 River
Page 108 and 109:
Page 110 and 111:
Water quality (n=24) Periphyton (n=
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138:
Appendix 1: Monitoring site details
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
show all

River and stream water quality and ecology - Greater Wellington ...

Create successful ePaper yourself

Delete template?

Save as template?