Water quality of New Zealand rivers based on the health of their macroinvertebrate community

Macroinvertebrates: Benthic macroinvertebrates are small animals without backbones (eg insects and worms). They live on and under submerged logs, rocks, and aquatic plants on the beds of rivers and streams during some part of their life cycle. Macroinvertebrates play a central role in stream ecosystems by feeding on periphyton (algae), macrophytes (aquatic plants), dead leaves and wood, or on each other.
MCI (macroinvertebrate community index): The MCI assigns ‘scores’ to taxa (types of macroinvertebrates) based on their tolerance to pollution. Scores for each taxa found at a site are combined and an overall MCI score is calculated: excellent (>119); good (100–119); fair (80–99) and poor (<80). A high macroinvertebrate community index (MCI) indicates a high level of river health.

Figure.NZ calculated the median, upper quartile, lower quartile, min and max clarity measures by land cover class. These calculations were undertaken to mirror the analysis undertaken for the Environmental Reporting Series (see https://data.mfe.govt.nz/table/2534-macroinvertebrate-community-index-percentiles-by-monitoring-site-2009-13/data/ Figure 1)

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For the analysis presented here, NIWA used MCI data from up to 512 river sites monitored by them and the 16 regional councils with consistent time periods and comparable methods (Larned et al, 2015).
Sites are classified by dominant land cover in the upstream catchment.