River habitat assessments are undertaken biennially by the Northland Regional Council (the council) at a selection of sites on rivers around the region. Sites assessed are all in the Regional River Water Quality Monitoring Network (RWQMN).
Habitat assessments follow the protocol detailed in Pfankuch D. J. (1975), Stream Reach Inventory and Channel Stability Evaluation. This allows for the quality of the riparian environment to be assessed (stream health), along with an estimate of the amount (quantity) of different habitats present and the stability of the environment.
Other data collected by the council is used to aid interpretation of results from the habitat assessments including results from the council's macroinvertebrate monitoring programme carried out in RWQMN.
This report presents the results from habitat assessments undertaken in 2010 and 2012. A total of 35 sites were assessed in 2010 and 2012. Also included in this report is some provisional trend analysis of results from the last four rounds of sampling (2005, 2007, 2008 and 2010).
In 2010, no sites recorded excellent stability, 13 sites recorded good stability, 14 sites recorded fair stability and two sites recorded poor stability. The two most stable sites were the Kaihu and Waipoua rivers.
Also in 2010, three sites recorded poor habitat, 16 sites recorded marginal habitat, 15 sites recorded sub-optimal habitat and no sites recorded optimal habitat. The two best sites were the Mangahahuru River at Main Road and Waipapa River at Forest Ranger.
In 2012, three sites recorded excellent stability, 14 sites recorded good stability, 16 sites recorded fair stability and two sites recorded poor stability. The two most stable sites were the Waipoua River and the Waipapa River at Forest Ranger.
Also in 2012, three sites recorded poor habitat quality, 18 recorded marginal habitat quality, 12 recorded sub-optimal habitat quality and two recorded optimal habitat quality. The two best sites were the Waipoua River and the Waipapa River at Forest Ranger.
Trends observed over five assessments – carried out in 2005, 2007, 2008, 2010 and 2012 – indicate that habitat quality has not improved at any sites and declined at four sites with the remaining 26 sites being stable. Results were inconclusive at five sites. In comparison, channel stability has improved at 10 sites, declined at two sites and remained stable at 15 sites. Results were inconclusive at eight sites.
Further investigation is required at sites with declining habitat quality and macroinvertebrate scores. Further investigation is also required at sites with declining stability in order to identify the cause of the decline, i.e. whether it is a result of land-use change or human activity, or natural events. Information collected through investigations will assist interpretation of results which will help in targeting land management in those areas.