Effects of land use and point source discharges on macroinvertebrate and periphyton communities of the Taranaki ring plain : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science at Massey University
Macroinvertebrate and periphyton communities were sampled from February 1998 to May 1998 in 83 stream and river sites throughout the Taranaki Ring Plain, New Zealand. Generally as streams descend the mountain, the catchment moves along a continuum ranging from pristine headwater streams with a high proportion of catchment in native forest, through to lowland streams with a high proportion of pasture catchment, draining intensive agricultural and industrial practices which put pressure on water resources. Ordination of sites indicated that the environmental continuum on the Ring Plain corresponds to a gradient of taxa along Axis 1 from clean water mayfly, caddisfly and stonefly taxa (i.e., Deleatidium spp., Coloburiscus) that prefer headwater streams, through to nutrient tolerant taxa (i.e. Oxyethira, Nemertea, Potomoprygus) that prefer lowland streams. This was emphasised by the positive correlation of Axis 1 with altitude and percent native forest and negative correlation with conductivity, chlorophyll a, temperature and BOD (Biological Oxygen Demand). A decline in invertebrate richness (number of taxa, Margarlef's index), and an increase in periphyton richness (number of taxa) and biomass (chlorophyll a) also occurred with distance downstream on the Ring Plain. Data collected in my study were compared to earlier studies (Taranaki Catchment Commission 1982,1984; Stark 1982; Hirsch 1958) to examine longer term temporal changes in macroinvertebrate communities. Significant differences in MCI and the SQMCI were found between my study and studies in the 1980's and 1958, as well as differences in percent EPT and the number of taxa between my study and 1980's studies. The decline in biotic indices in my study was also accompanied by a decrease in the abundance of mayfly and sensitive caddisfly taxa (i.e., Deleatidium spp., Coloburiscus) and an increase in the abundance of Diptera and the more tolerant caddisfly taxa (i.e. Oxyethira, Tanytarsini), since 1980's studies. Although invertebrate communities in my study that used to be below dairy factories and septic tank discharges were similar to the invertebrate communities in the 1980's studies, there was a general improvement since the 1958 study. This recovery was reflected in the smaller negative differences in MCI values between sites directly upstream and downstream of discharge points within my study compared to the 1958 study. Temporal changes in water quality were mostly attributed to the intensification of agricultural practices, point source discharges from dairy factories and industry, changes in the flow regime and sand movement.