72 Figure 17: NMDS ordination of a) spring and b) autumn macroinvertebrate communities for sites on the Ohinemuri River, 2009-2021. Data from OGNZL biomonitoring programme. 13.6.3 Periphyton Periphyton is also sampled as part of the OGNZL treated water discharge monitoring. As for other biological parameters the results can be variable but ranges from dominance of diatoms to filamentous algae. Summaries of the Chlorophyll-a (chl-a) for each of four monitoring sites (OH3, OH5, OH1 and OH6) for the period 2008-2021 are provided Figure 20. The results highlight the absence of high variability between the sites upstream-downstream over the monitoring period (Figure 18: F3, 568 = 1.47, p = 0.22). Chl-a concentration appears to show minimal variability from 2008 – 2017; however, 2018 to 2021 results indicate an increase in chl-a concentrations (KruskalWallis: H(13) = 231.95, p < 0.001), exceeding guidelines for the protection of benthic biodiversity (50 mg/m2, Biggs 2000). Mean (±SE) spring data had higher chl-a concentrations compared to autumn (71.4 ± 8.3 and 38.8 ± 3.4 mg/ m2, respectively). This is more notable in 2021 where algal standing crop or biomass exceed the guidelines for the degradation of higher communities such as trout (= 200 mg/m2 chlorophyll-a – see guideline in Biggs 2000; Figure 7b). Summaries of the Ash-Free Dry Weight (AFDW) for each of four monitoring sites (OH3, OH5, OH1 and OH6) for the period 2008-2021 are provided in Figure 19. The New Zealand Periphyton Guidelines recommend a maximum AFDW of 35 g/m2 for the protection of trout habitat and angling. The results highlight the absence of high variability between the sites b) a)
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