Biomonitoring, and the macroinvertebrate faunas of Canterbury streams. (2001)
AuthorsWright-Stow, Aslan E.show all
A wide-ranging macroinvertebrate and physico-chemical survey of 230 3rd and 4th order streams throughout the Canterbury region was conducted between November 1999 and March 2000. Kick-net sampling, spot water sampling and habitat surveys were used. Invertebrate community composition appeared to be influenced by two overriding factors; the physical condition of the stream, and the amount of anthropogenic development within the catchment. Faunas dominated by Ephemeroptera and Trichoptera and with some Plecoptera present tended to occur in pristine high altitude streams with low conductivity, well vegetated riparian zones, heterogeneous streambed substrates and periphyton consisting primarily of diatom biofilms. Faunas dominated by Crustacea, Oligochaeta and Chironomidae occurred commonly at degraded lowland sites with high conductivity, little or no riparian vegetation, more homogeneous fine substrates and periphyton dominated by thick mats and filaments. Between these two extremes, gradual change in faunas was found, with Trichoptera dominating intermediately disturbed sites. A striking decrease in the relative abundance of Ephemeroptera along an ecological gradient appeared to be associated with increasing intensity of landuse. A comparative investigation of three biotic indices widely used in New Zealand for assessing stream health, indicated that the MCI, OMCI and SOMCI may not assess the health of all sites, consistently. The inconsistencies were probably brought about by two factors. Firstly, presence-absence data used in calculating the MCI may not detect subtle differences in community structure, whereas the quantitative data used by the OMCI and SOMCI may pick up small differences and therefore group sites into different degradation bands. Secondly, published degradation bands for the MCI, OMCI and SOMCI do not appear to be directly comparable in Canterbury. The utility of a quantitative MCI with low-level (order, class, phylum) identification was also investigated, and found to be a potentially viable alternative to the MCI and its derivatives when a low-cost, rapid assessment technique is needed, but expertise in identification is lacking. The health of streams in the Canterbury region as assessed by the MCI, was investigated. The MCI indicated that streams were generally more healthy if they were further inland, at higher altitudes, and were in forested or unmodified catchments. Stream health was poorest in lowland sites with pastoral and urban/city developed catchments, although 42 pastoral sites with MCI values> 100 and taxonomic richness >25 indicated that healthy streams were attainable in agriculturally developed land. Finally, a multimetric approach for assessing the health of Banks Peninsula streams using macroinvertebrates was developed. Five biological metrics (OMCI, % EPT, % Chironomidae, % Mollusca, No. Ephemeroptera) that best discriminated selected reference sites from sites impaired by habitat disturbance and organic pollution were combined into an index of biological integrity; the Banks Peninsula Macroinvertebrate Index (BPMI). Strong relationships between the BPMI and MCI and OMCI suggested that the extra effort required to produce a multimetric index did not result in improved assessment of stream condition. However, a multimetric index can provide additional information on the source of degradation to a stream and indicate where restoration or mitigation should be focussed.