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

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River and stream water quality and ecology in the Wellington region: State and trends Table 4.12: Summary of meaningful trends (ie, p1% per year) in DRP and TP concentrations (mg/L) recorded at RSoE sites over July 2006 to June 2011. MASS=median annual Sen slope (mg/L/yr) calculated using the Seasonal Kendall test. The arrow indicates the direction of the trend Site Site name Median n MASS Raw data Flow-adjusted data Rate of change (%/year) Trend n MASS Rate of change (%/year) Dissolved reactive phosphorus (DRP) RS03 Waitohu S at Forest Pk 0.008 59 0.001 7.1 ↑ 57 0.001 8.6 ↑ RS11 Whareroa S at Waterfall Rd 0.029 60 -0.002 -6.3 ↓ No trend RS15 Porirua S at Glenside 0.019 60 -0.002 -8.0 ↓ No trend RS17 Makara S at Kennels 0.029 60 -0.002 -5.5 ↓ No trend RS18 Karori S at Makara Peak 0.039 60 -0.004 -9.6 ↓ 60 -0.002 -5.4 ↓ RS19 Kaiwharawhara S at Ngaio Gorge 0.034 60 -0.006 -17.5 ↓ 60 -0.004 -12.3 ↓ RS24 Mangaroa R at Te Marua 0.010 60 0.001 13.0 ↑ 59 0.001 12.9 ↑ RS28 Wainuiomata R at Manuka Trk 0.010 58 0.001 6.1 ↑ 57 0.000 5.0 ↑ RS33 Ruamahanga R at Gladstone Br 0.024 60 -0.002 -8.3 ↓ No trend RS36 Taueru R at Castlehill 0.008 No trend 60 0.000 6.5 ↑ RS39 Whangaehu R 250 u/s confl. 0.030 60 0.007 22.5 ↑ Not assessed (no flow data) Total phosphorus (TP) RS05 Otaki R at Pukehinau 0.007 60 -0.001 -12.1 ↓ 60 -0.001 -10.8 ↓ RS06 Otaki R at Mouth 0.007 60 -0.001 -15.0 ↓ 60 -0.001 -13.7 ↓ RS09 Waikanae R at Mangaone Wk 0.015 60 -0.001 -10.3 ↓ 60 -0.001 -7.9 ↓ RS12 Whareroa S at QE Park 0.082 No trend 57 -0.003 -4.1 ↓ RS13 Horokiri S at Snodgrass 0.019 60 -0.002 -11.4 ↓ 59 -0.002 -12.0 ↓ RS14 Pauatahanui S at Elmwood Br 0.031 60 -0.002 -7.2 ↓ 60 -0.003 -8.6 ↓ RS15 Porirua S at Glenside 0.031 60 -0.004 -11.8 ↓ 60 -0.004 -14.4 ↓ RS18 Karori S at Makara Peak 0.051 60 -0.004 -8.6 ↓ 60 -0.003 -5.8 ↓ RS19 Kaiwharawhara S at Ngaio Gorge 0.049 60 -0.006 -11.5 ↓ 60 -0.005 -10.0 ↓ RS20 Hutt R at Te Marua Intake Site 0.007 No trend 60 -0.001 -8.7 ↓ RS27 Waiwhetu S at Wainui Hill Br 0.064 59 -0.008 -11.8 ↓ No trend RS28 Wainuiomata R at Manuka Trk 0.015 58 -0.001 -6.7 ↓ 57 -0.001 -5.6 ↓ RS29 Wainuiomata R u/s of White Br 0.023 59 -0.003 -13.1 ↓ 59 -0.002 -8.7 ↓ RS39 Whangaehu R 250 u/s confl. 0.065 60 0.012 18.1 ↑ Not assessed (no flow data) RS49 Beef Ck at Headwaters 0.011 60 -0.001 -6.5 ↓ Not assessed (no flow data) RS50 Mangatarere S at SH 2 0.105 60 -0.009 -8.9 ↓ No trend RS52 Tauanui R at Whakatomotomo 0.009 59 -0.001 -8.2 ↓ 59 -0.001 -8.9 ↓ WGN_DOCS-#1100598-V3 PAGE 51 OF 160 Trend Overall, improving trends in DRP concentrations were demonstrated at six sites, five of which are classed as urban or pastoral (the forested Whareroa Stream at Waterfall Road was the exception). However, despite some relatively large rates of improvement exhibited at these sites (eg, DRP concentrations at Kaiwharawhara Stream at Ngaio Gorge decreased 0.006 mg/L/year (-17.5%/year), the state analysis (refer Table 4.2) indicates that median DRP concentrations at all six sites are typically well above the ANZECC (2000) lowland TV of 0.010 mg/L. In contrast, at four of the five sites that exhibited a meaningful increase in DRP concentration, median concentrations for the state period are just below – or in the case of Mangaroa River at Te Marua (Figure 4.19), now just above – the ANZECC (2000) lowland TV. Of these five sites, two are reference sites
River and stream water quality and ecology in the Wellington region: State and trends (Waitohu Stream at Forest Park and Wainuiomata River at Manuka Track) and the remaining three are located in catchments dominated by pastoral landcover. The largest rate of increase was observed at Whangaehu River 250 m from confluence (0.007 mg/L/year) (Table 4.12). Figure 4.19: DRP concentrations recorded in the Mangaroa River at Te Marua, based on monthly monitoring over July 2006 to June 2011. The red and black lines denote the ANZECC (2000) lowland TV and the direction of the trend in concentrations, respectively Whangaehu River 250 m from confluence was the only site to record a meaningful increase in TP concentration. As noted earlier in this section, this site drains a portion of the erosion-prone eastern Wairarapa hill country and the increase in TP concentration of 0.012 mg/L/year (Table 4.13) coincided with both a decrease in visual clarity (-0.13 cm/year) and an increase in turbidity of more than 0.9 NTU/year (refer Tables 4.8 and 4.9). While this suggests that increasing TP concentrations might be related to increased sediment entering the Whangaehu River, no flow-adjusted trend assessments were able to be performed for this site (ie, the observed trends may be flow-related). Similar to the nitrogen trend results, a number (7) of the 16 sites that showed improving trends in concentrations of TP are either reference sites or sites with upstream catchments dominated by indigenous forest cover (eg, Otaki River at Mouth and Hutt River at Te Marua). This suggests that many of the improving trends may be related to natural factors (eg, climate variability). It is also noted that five of the other nine sites that exhibited improvements in TP concentrations still recorded elevated median concentrations (relative to the ANZECC (2000) lowland TV) in the state analysis, particularly Mangatarere Stream at SH 2 (see Table 4.2). PAGE 52 OF 160 WGN_DOCS-#1100598-V3
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DISCLAIMER This report has been pre
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observed trends were unclear. The p
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5. Periphyton - state and trends 57
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Water quality (n=24) Periphyton (n=
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Appendix 1: Monitoring site details
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