U:\2021\BM210482_IBo_Waihi_North_Project\Documents\WNP_Freshwater_Report_May_2022\FINAL_Freshwater_Report_FOR DELIVERY_June 2022\FINAL DELIVERED 17 JUNE 2022\WAI-985-000-REP-LC-0007_Rev0_Freshwater_20220621_FINAL.docx upstream to downstream over the monitoring period (Figure 19: F3, 568 = 1.42, p = 0.24). Similar to Chl-a concentration, AFDW appears to show minimal variability from 2008 – 2017 with an increase from 2018 (Kruskal-Wallis: H(13) = 244.89, p < 0.001), with Spring 2021 exceeding guidelines for the protection of benthic biodiversity (35 g/m2). On average (±SE) spring has higher AFDW compared to autumn sampling (14.2 ± 1.5 and 7.5 ± 0.6 g/ 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 (35 g/m2 AFDW; Figure 18b). The form of data collection changed after 2017. Therefore, ordinations of the periphyton communities after this date are unavailable but are shown for 2010-2017 (Figure 20). The ordinations reveal patterns in the overall data. As outlined for the macroinvertebrates above, the smaller the cluster for each site (shown in different colours in Figure 20), means a higher degree of similarity (that is, the communities of periphyton over the years have not changed greatly). The broader the spread of each site cluster the more dissimilarity is exhibited within the site data. Greatest variation of periphyton communities over the sampling occurred at Site OH5 during autumn, and OH1 during spring. However, as for the macroinvertebrate communities, for the most part, the clusters of periphyton communities shown in Figure 20 are on top of each other, in a like-pattern. This indicates a very high degree of similarity between the sites, both in autumn and spring. In part, this is expected, given the sample sites occur over a relatively short stretch of river with generally consistent habitat conditions. More importantly, it shows that the periphyton communities at sites downstream of the treated wastewater discharge are very similar to the periphyton communities above the discharge (or put another way, do not deviate from the control site condition). Above all it shows that the ecological values as assessed by periphyton have remained consistent throughout the monitoring period and since the mine commenced operating in the 1980s. 13.6.4 NOF for Periphyton The NOF sets out limits for periphyton for the ecosystem health (aquatic life) objective for freshwater in New Zealand. These limits relate to chlorophyll-a concentrations and are set out in attribute bands for condition of water quality for ecosystem health. The limits for each attribute band are set out to nutrient enrichment and/or alteration to flow regime or habitat. The NOF attribute bands are set out in Appendix 12. For the most part, the periphyton levels within the Ohinemuri River were above the NBL, although since 2018, median Chl-a levels have gradually increased and in spring 2021 fell below the NBL (>200 mg/m2, Figure 18). 13.6.5 Fish Shortfin eels and common bullies were the most widespread and common species recorded during monitoring, but longfin eels, Cran’s Bully, and rainbow trout were all recorded during monitoring surveys. Banded kokopu have been recorded in earlier surveys. Several of the 41 species of native fish of New Zealand are ‘diadromous’ or ‘sea run’, which means that they migrate between freshwater and saltwater during some part of their life cycle (McDowall 1990). Species such as longfin and shortfin eels, require migration to the sea for breeding; others such as banded kokopu require passage for young larva to the sea for growth
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