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 4.1.5 pH Median pH values recorded across the 55 RSoE sites ranged from 6.4 (Parkvale Stream tributary at Lowes Reserve) to 8.0 (Huangarua River at Ponatahi Bridge and Awhea River at Tora Road) (Table 4.2). Sites located in catchments that drain the eastern Wairarapa hill country tended to have higher median pH values than sites located elsewhere (Figure 4.6), probably reflecting the carbonate-rich Miocene-Pliocene rocks/geology of marine origin present in this part of the region (Daughney 2010). Only Parkvale tributary at Lowes Reserve recorded a median pH value outside of the ANZECC (1992) range of 6.5 to 9. The slightly acidic pH is likely to be a natural feature of this waterway; the majority of the flow in this stream is considered to be sourced from groundwater (Daughney 2010) with springs originating from within a remnant area of kahikatea swamp forest. pH 8.2 8.0 7.8 7.6 7.4 7.2 7.0 6.8 6.6 6.4 6.2 n =12 n =43 Eastern Wairarapa hill country Rest Figure 4.6: Box plots showing the range of median pH values measured at RSoE sites draining the eastern Wairarapa hill country compared with elsewhere, based on monthly sampling between July 2008 and June 2011. The difference between medians was statistically significant (Mann-Whitney Rank Sum Test, p
River and stream water quality and ecology in the Wellington region: State and trends indigenous forest landcover and lower at low elevation sites with a pastoral or urban REC landcover class; the opposite pattern was observed for turbidity and total suspended solids (TSS) (Figure 4.7). Median visual clarity values at 31 sites failed to comply with the MfE (1994) guideline over the reporting period and median turbidity values at 11 of these sites were also above the ANZECC (2000) lowland TV of 5.6 NTU (Table 4.2). Visual clarity (m) 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 REC landcover class Indigenous forest Exotic forest Pastoral Urban MfE (1994) guideline 0.0 0 10 20 30 40 50 60 70 80 90 100 % of upstream catchment in indigenous forest landcover Alluvium Hard-sedimentary Soft-sedimentary PAGE 30 OF 160 WGN_DOCS-#1100598-V3 Maximum TSS (mg/L) 1400 1200 1000 800 600 400 200 0 n =5 n =38 n =12 Figure 4.7: Scatter plot (left) of indigenous forest cover in the upstream catchment against median visual clarity values for each RSoE site, and box plot (right) summarising maximum TSS concentrations recorded at RSoE sites grouped by REC geology class. Both plots are based on the results of monthly sampling between July 2008 and June 2011 The highest median TSS concentration was recorded at Ruamahanga River at Pukio (18 mg/L). The next highest median TSS concentrations were recorded at Parkvale Stream at Weir (7.2 mg/L), Whareama River at Gauge (6.5 mg/L), Ruamahanga River at Te Ore Ore (6.4 mg/L) and Taueru River at Gladstone (6 mg/L). As expected, the highest maximum TSS concentrations were recorded during or following wet weather, and typically at RSoE sites with highly erodible soft-sedimentary soils/geology (Figure 4.7). These are generally sites draining the eastern Wairarapa (eg, Awhea River at Tora Road (950 mg/L), Whareama River at Gauge (1,200 mg/L), and Mataikona tributary at Sugar Loaf Road (1,320 mg/L)). However, the site that recorded the highest TSS concentration over the reporting period was Orongorongo River at Orongorongo Station (1,390 mg/L); this river has its headwaters in the Rimutaka Range (ie, hard-sedimentary geology). While lower visual clarity values (and higher TSS concentrations and turbidity values) recorded at individual sites were generally associated with higher flows, there were some exceptions when activities such as instream works, stock access (eg, Parkvale Stream at Weir – see Section 4.1.11) or pollution events impacted on water clarity during dry weather/stable flow conditions. For example, a visual clarity value of just 0.30 m was recorded at Waingawa River at South Road during dry weather/stable flow conditions on 27 January 2009. This low result coincided with flood protection works being undertaken upstream of the site. A similarly poor visual clarity value (0.38 m) recorded during dry conditions at Hutt River at Boulcott on 7 October 2010 also coincided with instream flood protection works (visual clarity measured on the same day at Hutt River at Manor Park upstream of the works was 2.03 m).
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Page 5 and 6: observed trends were unclear. The p
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River and stream water quality and
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RS06 Shade RS11 Habitat RS35 RS49 R
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IBI Score 60 50 40 30 20 10 0 River
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Water quality (n=24) Periphyton (n=
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Appendix 1: Monitoring site details
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