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 13.6 Ecological Condition of the Ohinemuri River at Waihi 13.6.1 Background The ecological condition of the Ohinemuri River in the vicinity of the Waihi mining operation is best informed by the consent monitoring undertaken by OGNZL. As described above, the monitoring programme is comprehensive and requires that habitat, algae, macroinvertebrates and fish are surveyed at regular intervals. The most recent survey data is provided in Ryder (2021) but reports on baseline studies and regular monitoring extend back to 1983. We have not attempted to summarise all of the previous information here; rather we have drawn on the most recent monitoring data, as well as data from the WRC SOE monitoring programmes to inform our discussion on the condition of the Ohinemuri River at Waihi. 13.6.2 Macroinvertebrates We have used the WRC SOE macroinvertebrate monitoring data to highlight the ecological condition of the Ohinemuri River upstream of Waihi. The ecological condition of the Ohinemuri River catchment at the SH25 site upstream of Waihi shows considerable variation over the 23year record as recorded from the WRC state of the environment monitoring programme (Table 23). In recent years the condition of the river, as measured by the Macroinvertebrate Community Index (MCI), has been poor-fair, and this is reflected in the results of the OGNZL inriver biological monitoring (Table 24). The increase in taxa number represents a shift in the community composition to a more tolerant fauna, largely dominated by dipteran flies and worms21. Summaries of the macroinvertebrate biological indices (MCI and QMCI) for each of four monitoring sites in the Ohinemuri River undertaken by OGNZL (OH3, OH5, OH1 and OH6) for the period 2003-2021 are shown in Figure 15 and Figure 16. The results reflect the poor/fair condition of the river discussed above, as measured by these metrics. Over this longitudinal study (2003 – 2021) the mean MCI was 81.3 (Fair), this score increased during the spring season by an average of 4 points (F1, 1198 = 83.23, p < 0.001). Differences were also found between years (F18, 1181 = 13.93, p < 0.001), however no apparent trend was observed (linear regression; R2 = 0.008). QMCI results also showed an increased value in spring (F1, 1198 = 13.87, p < 0.001) and fluctuated throughout the sampling time period (F18, 1181 = 58.31, p < 0.001). However, no trend was observed (linear regression; R2 = 0.11). We note that the MCI values recorded as below a score of 90, or QMCI scores below 4.5 would be below the National Bottom Line provided for by the NPS-FM (2020). 21 It is worth noting that some of the variance in the metrics will have come from different levels of taxonomic penetration of the macroinvertebrate sample data.
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