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

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RS06 Shade RS11 Habitat RS35 RS49 RS43 RS44 RS54 RS09 Black disc RS28 Substrate Cond. TOC RS03 RS20 RS52 RS56 RS26 RS17 RS25 RS23 RS10 RS24 RS13 RS14 RS29 RS40 RS50 Amm N RS38 DRP TP TN TKN RS05 RS31 RS47 RS55 RS48 RS21 RS32 RS41 RS22 DIN RS37 RS51 Turb. RS16 Temp. RS15 RS18 RS46 RS33 RS34 RS30 River and stream water quality and ecology in the Wellington region: State and trends RS19 RS07 RS02 RS12 Landcover U IF P EF WGN_DOCS-#1100598-V3 PAGE 81 OF 160 RS36 RS53 RS45 RS04 RS42 2D Stress: 0.11 Figure 6.5: NMDS ordination of macroinvertebrate community composition based on mean taxon abundance at each of 55 RSoE sites determined from samples collected annually in 2009, 2010 and 2011. Environmental variables with a Spearman Rank correlation greater than rs=0.6 are shown by the overlain vectors most strongly correlated with macroinvertebrate community composition was TKN (rs=0.68), while the strongest two variable solution included TKN and substrate size (rs=0.81). This suggests that of the environmental variables measured, nitrogen enrichment and substrate size are most strongly linked with macroinvertebrate community composition. 6.2 Temporal trends 6.2.1 Approach to analysis Temporal trends were analysed over the period 2004 to 2011 (n=8) 24 . The approach used was similar to that of Collier and Kelly (2006) who analysed trends in macroinvertebrate metrics in a dataset over a similar length of record. The 2004 to 2011 period was the longest available for trend assessment since major changes were made to the RSoE site network in 2003 (refer Section 2.1). The September 2003 start date also represented a logical follow-on from the 1999 to 2003 trend period used to report on macroinvertebrate health in the last river and stream SoE technical report (Milne & Perrie 2005). Non-parametric Spearman Rank correlations (performed in SigmaPlot, version 11.0) were used to assess trends in four metrics: MCI (hard-bottomed), QMCI, %EPT taxa 25 and %EPT individuals 25 . As with the periphyton trend analysis (refer to Section 5.2), three trend classes were defined. Trends were considered ‘possible’ when Spearman Rank correlation coefficient probabilities (p) were between 0.1 and 0.05, ‘probable’ when p
River and stream water quality and ecology in the Wellington region: State and trends software (version 3.20). While all trend classes are summarised, only ‘probable’ and ‘clear’ trends are presented and discussed. For sites where trends were present, a linear regression line was fitted and the slope of this line used to provide some context for the rate of change or the magnitude of the trend at each site. The relative rate of change was also calculated by dividing the slope by the mean macroinvertebrate metric value. While useful indicators of macroinvertebrate community health, trends in abundance-based metrics (eg, QMCI and %EPT individuals) should be interpreted with caution as these metrics are more likely to be influenced by changes in sampling intensity, micro-scale habitat variables and fluctuations in the numbers of tolerant taxa than other presence/absence based metrics (Collier et al. 1998; Scarsbrook et al. 2000). 6.2.2 Results The trend analysis results are summarised in Table 6.3. Across all four of the metrics assessed, the majority of RSoE sites were typically stable over the seven-year reporting period (78% to 87% of sites depending on the metric). More trends were apparent in MCI than in the other metrics, although half of these were deemed ‘possible’ trends. The majority (83%) of all trends (possible, probable and clear) were indicative of deteriorating invertebrate community health. Only ‘clear’ and ‘probable’ trends (summarised in Table 6.4) are discussed further. The complete set of trend analysis results can be found in Appendix 7. Table 6.3: Number of RSoE sites assigned into different trend categories for each of four macroinvertebrate metrics, determined by performing Spearman Rank correlations on macroinvertebrate results from annual sampling at 55 sites between 2004 and 2011 Metric Deteriorating trend Possible Probable Clear decline decline decline Total No trend Improving trend Possible increase Probable Clear increase increase Total MCI 5 1 4 10 43 1 1 0 2 QMCI 2 3 3 8 47 0 0 0 0 %EPT taxa 2 4 1 7 48 0 0 0 0 %EPT individuals 2 1 2 5 46 1 2 1 4 Sixteen sites (29%) demonstrated at least one ‘clear’ or ‘probable’ trend in one of the four metrics assessed (Table 6.4), with 23 trends detected in total. Three sites exhibited trends in two metrics (Mangapouri Stream at Bennetts Road, Waiwhetu Stream at Wainuiomata Hill Bridge and Waingawa River at South Road) and two sites exhibited trends in three metrics (Whareroa Stream at Waterfall Road and Kopuaranga River at Stewarts). Of the sites with trends in two or more metrics all but one of the trends detected were indicative of deterioration. The exception was Mangapouri Stream at Bennetts Road, where an improving trend in MCI coincided with a deteriorating trend in QMCI. This site, along with three other sites (Waitohu Stream at Forest Park, Ruamahanga River at Pukio and Waiohine River at Gorge) also exhibited an improving trend in %EPT individuals. PAGE 82 OF 160 WGN_DOCS-#1100598-V3
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River and stream water quality and
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DISCLAIMER This report has been pre
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observed trends were unclear. The p
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