Macroinvertebrate results summary


Waiarohia Stream sites

Similarly to last year the three of the Waiarohia Stream sites; at Rust Ave Bridge, at the Northern Russell Road Bridge and Whau Valley Road, had macroinvertebrate communities associated with moderate water quality and impacted stream ecosystem. While the small tributary that flows from Kamo into Waiarohia Stream had macroinvertebrate index scores indicative of a severely degraded stream with poor water quality.

River Water Quality Monitoring Network Sites

Of the 19 RWQMN sites monitored in 2006 only two sites had biotic indices results that showed the stream ecosystem is still in a relatively pristine state (i.e. no or very little impact from humans); the Waipoua River site in Waipoua Forest and Waipapa River site in Puketi Forest. This is consistent with the water quality results for these sites.

There is only one site, Waitangi River at Waimate North, that has macroinvertebrate index scores that indicate a slightly impacted stream ecosystem and/or mild water pollution, compared to four in 2005. Of most concern is Victoria River at Thompsons Bridge, which has had a significant change in its macroinvertebrate communities in the last year. This could indicate a deterioration in water quality, however this site is still ranked amongst the best sites of the RWQMN sites in terms of its water quality results for 2005-2006.

The macroinvertebrate results indicate that the following sites are severely impacted and/or have poor water quality:

  • Waitangi River at Watea
  • Wairua River at Purua
  • Mangakahia at Twin bridges

Otarao catchment sites

The Otarao stream is a relatively small catchment which flows into the Mangakahia River near Titoki which is the subject of an integrated catchment management project. The Regional Council, New Zealand Landcare Trust, Mangakahia Landcare Group and landowners within the catchment have been working together for four years with the overall aim of improving water quality in the Otarao stream. This includes work such as farm workshops, fencing and planting days, farm mapping and water quality and macroinvertebrate monitoring.

Of the four sites monitored for macroinvertebrates in 2006 the native forest site (Ruahuia Stream) in the headwaters is still in a relatively pristine state, while the lowest site in the catchment near Mangakahia River is the most degraded, with macroinvertebrate communities indicative of poor water quality. The macroinvertebrate communities for the other two sites on the Otarao Stream, which are mid catchment, indicate moderately to severely impacted water quality and stream health.

Resource Consent sites

In 2006 macroinvertebrate communities upstream and downstream of two dams in Northland were sampled. The results show a difference in macroinvertebrate communities at both dams upstream and downstream, with the macroinvertebrate index scores for downstream showing poorer water quality or more degradation when compared to the upstream sample. However some of this difference is most likely as a result of differences in surrounding land use.

Likewise macroinvertebrates were monitored upstream and downstream of two oxidation pond discharges and similarly to the dams both downstream sites had macroinvertebrate index scores indicating worse water quality or more impacted stream health than the upstream sites.

Macroinvertebrates are also sampled every year upstream and downstream of the discharges from an operating quarry and meatworks. Similarly to last years results, the 2006 macroinvertebrate results show that neither of these operations appear to be having a detrimental effect on water quality or stream health.

For more detailed information on the 2006 macroinvertebrate survey results or changes in macroinvertebrate communities over time, check out the detailed report available on the Regional Council Website.