Environmental factors affecting the taxonomic composition of aquatic macroinvertebrate communities in lowland waterways of Northland, New Zealand

Environmental data and aquatic macroinvertebrates colonising macrophytes or stones were collected at 29 stream and river sites in Northland, New Zealand, in February 1994 to elucidate environmental factors influencing the taxonomic composition of invertebrate communities. The 84 taxa recorded in February comprised predominantly Trichoptera (24 taxa), Ephemeroptera (17), and Diptera (14). Substrate type (macrophytes or stones) and percentage of native forest up stream or in the riparian zone appeared to be factors affecting classification of sites in TWINSPAN. Although catchment land use or riparian vegetation were not implicated as major factors affecting taxonomic richness or overall community composition (as indicated by DECORANA) at stony sites, the number of mayfly, stonefly, and caddisfly taxa was significantly correlated with the proportion of native forest cover in the riparian zone. Overall taxonomic richness and community composition appeared to be affected by small- to medium-scale factors such as water temperature, shade ratio, or riffle depth; with channel slope, substrate size, water conductivity, and degree of urbanisation in the catchment having secondary effects on community composition. The Macroinvertebrate Community Index was significantly correlated with a number of in-stream factors and also appeared to be influenced by catchment land use and riparian vegetation. Retention of native trees in riparian areas and the planting of trees where appropriate to reduce water temperatures and light exposure appear to have potential for enhancing biodiversity of aquatic invertebrate faunas, especially the mayfly and caddisfly fauna, in lowland waterways of Northland.