Current state of water quality indicators in urban streams in New Zealand

Abstract

ABSTRACT National assessments have highlighted that urban streams have some of the poorest water quality in New Zealand, yet there has been no analysis focussing on these streams. In this study we defined urban streams as >15% catchment urban land cover and used monitoring data to assess several indicators of water quality including dissolved metals, nutrients, bacteria and the macroinvertebrate community index. We investigated associations between the indicators and urban land cover, imperviousness and geographic location. Water quality was highly variable, within and between monitored sites; and invariably poor when compared to water quality criteria. Dissolved zinc was positively related to the proportion of urban land cover and imperviousness in the upstream catchment. There were significant differences in ammoniacal-N, nitrate-N, turbidity, MCI, dissolved zinc and E. coli between geographic locations. The analysis indicates that if urban development continues in its current form, increases in urban land cover around New Zealand can be expected to result in further declines in water quality and a reduced likelihood that water quality objectives will be achieved at impacted locations.