26 7.4 Waiharakeke Stream 7.4.1 Background The Waiharakeke Stream catchment begins immediately north of the Mataura Stream catchment with numerous tributaries that feed into two branches. Both branches flowed in a north easterly direction before combining and eventually discharging into the Otahu River. Two assessment sites within the Waiharakeke Stream catchment were sampled on 26th of August 2020. 7.4.2 Waiharakeke Tributaries The two assessment sites were located on tributaries connecting to the main stems of the Waiharakeke Stream (main stem and right branch). Both reaches comprised similar habitat features. The watercourses flow at the base of mostly steeply graded gully systems and followed a natural flow-path with no modification observed across the assessed reaches. The hard-bottom stream beds consisted of a range of substrate including gravels, cobbles, boulders and bed rock. Silt and sand made up a small proportion and occurred behind logs or large rocks near the edge of the stream. In comparison, the unnamed tributary mostly contained silt and sand and gravels less than 32 mm. This is likely due to the small size of the watercourse as well as the lack of protection from stock which can cause erosion and bank slumping leading to a build-up of finer material. Detail of the stream morphology and substrate is provided in Appendix 4. 7.4.3 Macroinvertebrate Assemblages The Waiharakeke Stream had a diverse range of EPT taxa, although many of the species were recorded as low in abundance (Table 7). A diverse range of EPT taxa is indicative of reasonable water quality and instream habitat. We note that Waiharakeke Stream sites likely had a high flow, relative to baseline conditions, at the time of sampling which may have flushed individuals downstream and resulted in lower numbers of, not just EPT taxa but, all macroinvertebrates. This would explain the low macroinvertebrate abundance for the sample, despite abundant instream habitat. Indices from the Waiharakeke Stream sites were all indicative of “excellent” water and/or habitat quality6. Results from all samples reflect the abundance of sensitive EPT taxa. The SQMCI score considers the relative abundance of each taxa in the sample and is calculated using the proportional abundance of each scoring taxa. It is thus a better index of a community’s composition, whereas the MCI is strongly influenced by rare taxa which contribute to the MCI score disproportionally to their abundance. 6 Interpretation of the classification of MCI and QMCI scores is provided in Table 3-3 of Appendix 3 of this report.
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