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 4.1: ‘Guidelines’ and trigger values (TV) used to assess the current state of water quality in rivers and streams in the Wellington region. Variables and guidelines used in Greater Wellington’s Water Quality Index (GW WQI) and the CCME (2001) WQI presented later in this section are also indicated. See Appendix 3 for an explanation of the different variables in this table Variable ‘Guideline’ value Water temperature 1 (ºC) ≤25 Reference WGN_DOCS-#1100598-V3 PAGE 21 OF 160 GW WQI CCME WQI ≤19 1 Quinn and Hickey (1990) and Hay et al. (2007) — Regional Freshwater Plan (RFP) for Wellington (WRC 1999) – trout fishery & spawning — — Dissolved oxygen (% saturation) ≥80 RMA 1991 Third Schedule and WRC (1999) RFP ‘bottom line’ 2 pH 6.5–9.0 ANZECC (1992) 2 — — Visual clarity (m) ≥1.6 MfE (1994) – guideline for recreation3 Turbidity (NTU) ≤5.6 ANZECC (2000) lowland TV — — Nitrite-nitrate nitrogen (mg/L) ≤0.444 ANZECC (2000) lowland TV — Nitrate nitrogen (mg/L) ≤1.7 Hickey and Martin (2009) – recommended freshwater toxicity TV (95% protection level) — Ammoniacal nitrogen (mg/L) Dissolved inorganic nitrogen (mg/L) Total nitrogen (mg/L) Dissolved reactive phosphorus (mg/L) Total phosphorus (mg/L) E. coli (cfu/100mL) ≤0.021 ANZECC (2000) – lowland TV — Varies 4 ≤0.465 ANZECC (2000) – freshwater toxicity TV (95% protection level) and USEPA (2009) ANZECC (2000) – by addition of the nitritenitrate nitrogen and ammoniacal nitrogen TVs — — — ≤0.614 ANZECC (2000) – lowland TV — — ≤0.010 ANZECC (2000) – lowland TV ≤0.033 ANZECC (2000) – lowland TV — — ≤100 ANZECC (2000) – stock water TV — ≤550 MfE/MoH (2003) – action level for recreation (used as a less conservative proxy for stock water) — 1 There are no formal guidelines for water temperature, but temperatures above 19 oC are known to cause behavioural disturbance in trout (Hay et al. 2007) and exclude sensitive macroinvertebrate species such as stoneflies (Quinn & Hickey 1990). 2 The ANZECC (2000) default lowland TVs are considered overly stringent (see Milne & Perrie 2005). 3 The ANZECC (2000) default lowland TV is considered erroneous (see Milne & Perrie 2005) and MfE (1994) is used by default. 4 Ammonia toxicity varies with pH and temperature. Chronic toxicity was assessed on a sample by sample basis, taking into account pH and water temperature at the time of sampling and using the calculations in the ANZECC (2000) guidelines. Acute toxicity was examined in a similar way, except that toxicity was only assessed using pH at the time of sample collection, as per recommendations and equations in USEPA (2009). For the 10 RSoE sites where water samples were also analysed for selected heavy metals and metalloids, median dissolved concentrations were compared against site-specific, hardness-modified TVs for chronic toxicity (95% level of protection) in accordance with ANZECC (2000). Acute toxicity was examined by comparing individual concentrations against site-specific, hardnessmodified TVs based on recommendations and equations in USEPA (2009). Because water hardness is not part of the existing suite of variables analysed in the RSoE programme, the median water hardness determined from monthly monitoring over January 2008 to December 2008 was used as a proxy for water hardness conditions at the time of sample collection (see Appendix 1 for median hardness values).
River and stream water quality and ecology in the Wellington region: State and trends As well as a comparison against the guideline values listed in Table 4.1, the River Environment Classification (REC) was also used to help interpret water quality across the 55 RSoE sites. The main REC class used was landcover (see Appendix 2). Information on the proportion of different landcover types in each catchment was derived from MfE (2010). (a) Water quality indices Two water quality indices are presented in Section 4.1.13 to summarise overall water quality and facilitate inter-site comparisons. First, to provide a measure of consistency and allow comparisons with earlier technical reports on river water quality in the Wellington region, Greater Wellington’s water quality index (GW- WQI) developed by Milne and Perrie (2005) – and adapted by Perrie (2007) – was applied to median results from the 55 RSoE sites. The second index uses the methodology defined in the Canadian Water Quality Index (CCME 2001). CCME-type indices have already been trialled in several regions (eg, Auckland and Southland); more recently, this index has been recommended for further investigation in relation to national reporting of river water quality (Hudson et al. 2011). Further background and information on the application of the two water quality indices are provided in Appendix 5. The water quality variables and associated threshold values used in each index are listed in Table 4.1. (b) General data processing, analysis and presentation Data were initially screened for outliers and where there was cause for concern around the quality of a data value (eg, the field meter performance had been questioned by the field staff undertaking the sampling), these values were removed. During data processing, any water quality variables reported as less than or greater than detection limits (ie, censored data) were replaced by values one half of the detection limit or the detection limit respectively (eg, a value of 400 became 400). Considerable use of scatter plots and box-and-whisker plots (box plots) is made in this section to graphically summarise the median and range of measurements for various water quality variables and compare these between sampling sites and/or major REC landcover classes. All plots were generated in SigmaPlot (version 11.0). In terms of interpretation of the box plots: the lower and upper boundaries of the box represent the 25 th percentile and 75 th percentile of the data set, respectively (a minimum of three data points are needed to generate the box); the horizontal line within the box represents the median value; the ‘whiskers’ (error bars) extending above and below the box (interquartile range) represent the 90 th and 10 th respectively; and percentile values, the black dots represent outliers. 4.1.2 Summary statistics and compliance with guideline values – overview Summary statistics for selected ‘core’ water quality variables over the three-year period examined are presented for each RSoE site in Table 4.2. Compliance with PAGE 22 OF 160 WGN_DOCS-#1100598-V3
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