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 chemistry data undertaken by Daughney (2010) further shows that some RSoE sites have similar chemical signatures to groundwater, suggesting that groundwater potentially influences water quality at these sites for much of the year. Certainly a number of sites that recorded higher concentrations of NNN have been shown by Daughney (2010) to have hydraulic linkages with adjacent groundwater: Waitohu Stream at Norfolk Crescent, Mangapouri Stream at Bennetts Road, Mangaone Stream at Sims Road Bridge, Ngarara Stream at Field Way, Parkvale tributary at Lowes Reserve, Parkvale Stream at Weir, and Mangatarere Stream at SH 2. Nitrite-nitrate nitrogen (mg/L) 0.5 0.4 0.3 0.2 0.1 0.0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec WGN_DOCS-#1100598-V3 PAGE 33 OF 160 Nitrite-nitrate nitrogen (mg/L) Figure 4.10: Box plots of median NNN concentrations at RSoE sites classed by REC as indigenous forest (left, n=24) and pasture (right, n=23), grouped by month of sample collection. Both plots are based on data collected monthly between July 2008 and June 2011 (note the different scales on the y-axes) In terms of ammoniacal nitrogen (Amm N), the majority of monitoring sites recorded median concentrations below the ANZECC (2000) lowland TV (Table 4.2) and none exceeded ANZECC (2000) or USEPA (2009) toxicity TVs on any sampling occasion. All six of the sites that exceeded the lowland TV are located in catchments dominated by pastoral and/or urban land use, with five of these sites being small low elevation coastal streams (Mangapouri Stream at Bennetts Road, Mangaone Stream at Sims Road Bridge, Waiwhetu Stream at Wainuiomata Hill Bridge, Waitohu Stream at Norfolk Crescent and Whareroa Stream at Queen Elizabeth Park). The other site to exceed the TV was Mangatarere Stream at SH 2. This site is located approximately 1.2 km downstream of the Carterton WWTP discharge and recorded the highest median value of any site over the reporting period (0.10 mg/L). 4.1.10 Phosphorus Median dissolved reactive phosphorus (DRP) concentrations at the 55 RSoE sites ranged from less than the analytical detection limit (ie,
River and stream water quality and ecology in the Wellington region: State and trends Beef Creek at Headwaters, are also thought to have naturally ‘elevated’ DRP concentrations (Perrie 2007; Ausseil 2011). Based on median concentrations across the three major landcover types, urban sites recorded the highest concentrations of DRP, followed by pastoral sites (Figure 4.11). Although Mangatarere Stream at SH 2 is classified as a pastoral site, the very high median concentration at this site is attributed to the input of treated wastewater from Carterton township to the stream a short distance upstream (eg, Milne et al. 2010). Dissolved reactive phosphorus (mg/L) 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 REC landcover class Indigenous forest Exotic forest Pasture Urban ANZECC (2000) lowland TV 0.00 0 10 20 30 40 50 60 70 80 90 100 % of upstream catchment in indigenous forest landcover Indigenous forest Pastoral Urban PAGE 34 OF 160 WGN_DOCS-#1100598-V3 Dissolved reactive phosphorus (mg/L) 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 n =24 n =23 n =7 ANZECC (2000) lowland TV Figure 4.11: Scatter plot (left) of indigenous forest cover in the upstream catchment against median DRP concentrations for each RSoE site, and box plot (right) summarising the range of median DRP concentrations across the three main REC landcover classes represented by the RSoE network. Both plots are based on data collected monthly between July 2008 and June 2011 In contrast with NNN, there was no seasonal pattern in DRP concentrations common to the majority of sites. While some sites recorded higher DRP concentrations during the winter months, other sites showed the opposite pattern and at some sites no clear pattern was evident. Higher DRP concentrations recorded at some sites during low flows are generally consistent with some sort of point source discharge (eg, a WWTP discharge) or nutrientrich groundwater input (Ausseil 2011). This pattern appeared strongest at some of the urban sites, such as Karori Stream at Makara Peak (Figure 4.12). Dissolved reactive phosphorus (mg/L) 0.07 0.06 0.05 0.04 0.03 0.02 0.01 0.00 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Dissolved reactive phosphorus (mg/L) 0.06 0.05 0.04 0.03 0.02 0.01 0.00 0.0 0.2 0.4 0.6 0.8 1.0 2.5 Flow (m 3 /s) Figure 4.12: Median (and range) of DRP concentrations recorded at RSoE sites classed as urban (left, n=7) and scatter plot of flow and DRP concentrations recorded at Karori Stream at Makara Peak (right). Both plots data are based on data collected monthly between July 2008 and June 2011
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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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