ENVIRONMENTAL-FACTORS AFFECTING THE TAXONOMIC COMPOSITION OF AQUATIC MACROINVERTEBRATE COMMUNITIES IN LOWLAND WATERWAYS OF NORTHLAND, NEW-ZEALAND

Environmental data and aquatic macroinvertebrates colonising macrophyt es or stones were collected at 29 stream and river sites in Northland, New Zealand, in February 1994 to elucidate environmental factors infl uencing 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 o r stones) and percentage of native forest up stream or in the riparian zone appeared to be factors affecting classification of sites in TWIN SPAN. Although catchment land use or riparian vegetation were not impl icated as major factors affecting taxonomic richness or overall commun ity composition (as indicated by DECORANA) at stony sites, the number of mayfly, stonefly, and caddisfly taxa was significantly correlated w ith the proportion of native forest cover in the riparian zone. Overal l taxonomic richness and community composition appeared to be affected by small- to medium-scale factors such as water temperature, shade ra tio, or riffle depth; with channel slope, substrate size, water conduc tivity, and degree of urbanisation in the catchment having secondary e ffects on community composition. The Macroinvertebrate Community Index was significantly correlated with a number of in-stream factors and a lso appeared to be influenced by catchment land use and riparian veget ation. Retention of native trees in riparian areas and the planting of trees where appropriate to reduce water temperatures and light exposu re appear to have potential for enhancing biodiversity of aquatic inve rtebrate faunas, especially the mayfly and caddisfly fauna, in lowland waterways of Northland.