Physico‐chemical parameters and invertebrate faunas of three lake inflows and outlets in Westland, New Zealand

Abstract

Selected physico‐chemical factors and the composition of faunas in inflow and outlet streams of three South Westland lakes (Kaniere, Mapourika, and Wahapo) were investigated from December 1988 to January 1990. Three sampling sites were used in each river system, the first 1 km above the inlet, another immediately below the lake, and the third 1–5 km further downstream. Dissolved organic carbon concentrations, alkalinity, and conductivity were only slightly influenced by the presence of a lake. Summer and winter water temperatures were elevated at lake outlets, but generally declined again downstream. Substrate size, stability, and homogeneity were also greater at artificial lake outlets. Invertebrate taxonomic richness was lowest at lake outlets, intermediate in inlets streams, and greatest at downstream sites. Inflow stream faunas were dominated by Deleatidium (Ephemeroptera: Leptophlebiidae), whereas lake outlets were dominated by Hydropsychidae, Simuliidae, and Mollusca; downstream Simuliidae, Chironomidae, and Hydropsychidae remained dominant and plecopteran taxa increased. Species of Coleoptera, Ephemeroptera, and Plecoptera were poorly represented at lake outlets but numerous at inlet and downstream sites. Substrate heterogeneity and stability, mean depth, water velocity, and water temperature were implicated as important physical environmental factors affecting community composition in lake outlets.

Keywords:

• benthic invertebrates
• lake outlets
• regulated rivers
• New Zealand