Environmental monitoring and assessment of nuisance aquatic insects in three Christchurch waterways

Abstract

The Christchurch City Council regularly receives complaints from residents concerned with nuisance flying insects. This study uses biological monitoring and an assessment of community perception in and near three Christchurch waterways as methods to assess if waterway enhancement projects are increasing insect numbers and impacting on community well being.

The results suggest that it is highly likely that following habitat disturbance, numbers of nuisance aquatic larvae explode, then stabilise. This biological equilibrium appears to have been reached by the time that the outlet of the Wigram Retention Basin was monitored. Course's Stream also appears to be in equilibrium, with the high ecosystem diversity helping to control nuisance insects biologically. Consequently, the community in proximity to these sites perceived the impact of flying nuisance insects on their well being as minor.

Recent waterway enhancement and management projects appear to have significantly (p<0.005) increased the numbers of nuisance aquatic larvae in the Upper Styx catchment. Household proximity to a waterway appeared to be related to the perceived effect of flying insects. The high numbers of mosquito larvae in the Styx swamp appear to be the result of recent CCC work, and are affecting the well being of nearby residents. The high numbers of midge larvae in the Styx subdivision, apparently caused by a number of environmental factors, are also affecting the well being of nearby residents.

The effects of waterway enhancement and management projects need to be carefully considered in the context of community well being. Such projects need to be done with caution and preventative and mitigation measures anticipated.