An Evaluation of the appropriateness of two biological methods for assessing water quality: a study in the Wainuiomata River

Abstract

Macroinvertebrate and periphyton communities are commonly used to determine pollution impacts for water quality assessment. To date little work has been done comparing the two methods response to pollution in the same study. This thesis evaluates the usefulness of macroinvertebrate indices (MCI and SQMCI) against two measures of periphyton biomass (AFDM and chlorophyll a). Linear correlations of macroinvertebrate and periphyton statistics with a series of nutrient ions and conductivity were used to evaluate the performance of the two approaches. The Wainuiomata River was sampled in three contrasting seasons during 1998. A Surber sampler was used for macroinvertebrates; periphyton were sampled using both artificial substrates and the standing crop on the rocks in the stream. A single annual sample would be sufficient for Macroinvertebrate indices (MCI/SQMCI) but periphyton require more frequent sampling times, monthly being desirable. Artificial substrates were found to provide no more valuable information than the standing crop samples. The macroinvertebrate indices correlated more strongly with the nutrient and conductivity parameters than periphyton chlorophyll a and AFDM. Further work on periphyton to produce an index similar to MCI/SQMCI for New Zealand is recommended.