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 6.4: Summary of ‘probable’ and ‘clear’ trends in MCI, QMCI, %EPT individuals 1 and %EPT taxa 1 metrics, based on annual means derived from macroinvertebrate samples collected at 55 RSoE sites between 2004 and 2011 (n=8). Arrows indicate the direction of the trend, with a single arrow indicating a ‘probable’ trend (p
River and stream water quality and ecology in the Wellington region: State and trends The ecological significance of these trends is unclear. However, at some sites where a deteriorating trend in MCI was identified (eg, Whareroa Stream at Waterfall Road and Waiwhetu Stream at Wainuiomata Hill Road), the magnitude of the deteriorating trend resulted in the site moving into a lower macroinvertebrate class during the reporting period (Figure 6.6). Application of two thresholds used in other regions to identify ecologically significant trends – a relative rate of change greater than 1% per year and an overall change greater than 20% (Stark 2010; Collier & Hamer 2012) – resulted in all 23 and 16 trends, respectively, being classed as ecologically significant. However, these thresholds are considered arbitrary and so should be used with caution. For future reporting of macroinvertebrate metric trends it is recommended that alternative methods for assessing ecological significance be explored, including the method used by Collier and Hamer (2012); this method bases the threshold for ecological significance on the degree of ‘natural variation’ at reference sites over time. MCI score 140 120 100 80 60 RS11: Whareroa S - Waterfall Rd RS27: Waiwhetu S - Wainui Hill Br RS33: Ruamhanga R - Gladstone RS38: Kopuaranga R - Stewarts RS41: Waingawa R - South Rd Excellent Good 40 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Figure 6.6: Mean Macroinvertebrate Community Index (MCI) scores for samples collected annually between 2004 and 2011 from five RSoE sites where significant declining trends were detected. Red lines and the grey bands represent Stark and Maxted (2007) thresholds and corresponding fuzzy boundaries, respectively In general, no clear reasons could be found for the observed trends in macroinvertebrate metrics. However, corresponding trends in water quality or periphyton variables may have had a bearing on results at some sites. For example: The decline in %EPT taxa identified at Whangaehu River 250 m from confluence coincided with a deterioration in visual clarity and an increase in turbidity, dissolved reactive phosphorus and total phosphorus (based on non-flow adjusted data) (Section 4.2.2). PAGE 84 OF 160 WGN_DOCS-#1100598-V3 Fair Poor
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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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Figure 2.1: RSoE monitoring sites a
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2.4.2 Biological variables River an
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