The spatiotemporal pattern of macroinvertebrate community composition in two subtropical streams in north-eastern NSW, Australia

Brett Andrew McCulloch

This thesis describes a study which assessed the knowledge gaps regarding the variation, consistency and effectiveness of biotic indices to detect a level of ecosystem health in two subtropical streams in the context of spatial and temporal patterns of variability in water quality and macroinvertebrate community compositions during varying antecedent rainfall totals (ART) and daily flows. Macroinvertebrates were sampled in riffle and pool-edge habitats on three occasions over a one-year period at seven sites in Terania and Goolmangar Creeks in north-eastern NSW, Australia. The biotic indices Australian River Assessment System (AUSRIVAS), SIGNAL2 score and the environmental filters model were used as indicators of stream health. Physical and chemical parameters were measured and compared with macroinvertebrate data observed in the study and the biotic data were also compared with samples collected by NSW Environment Protection Authority (NSWEPA) in the study creeks. Habitat for macroinvertebrates was assessed with a visual-based habitat assessment (HABSCORE). The study found physical and chemical parameters and macroinvertebrate assemblages in riffles and edge habitats varied among seasons, sites and between creeks. The study also observed significant spatial and temporal variation in biotic indices and the values for biotic indices differed under temporal changes in environmental variables. It is considered that the temporal variability among biotic indices may be partly a result of the effects of anthropogenic activities, natural seasonal variability in ART and daily flows as well as a result of the non-seasonal drought prior to sampling in summer (2003). The values of biotic indices were higher on Terania Creek compared to the more agriculturally oriented Goolmangar Creek. For both creeks, the highest values for most biotic indices were observed at sites located in the upper reaches and the lowest values downstream at sites more impacted by human pressure. It was considered that all the biotic indices effectively indicated a gradient of human pressure among sites and between creeks. The biotic indices were found to be somewhat independent of each other and the responses of the indices to environmental factors (natural and human-generated) varied. The majority of biotic indices were sensitive to factors such as altitude, water quality and land-use activities. The study found SIGNAL to be the most sensitive of the indices to seasonal variations in water quality and AUSRIVAS and environmental filters models effectively indicated seasonal variation in taxa diversity. The biotic indices applied in the study complemented each other, with each providing insights regarding assessment of the health of the study creeks. It is recommended that, when using biotic indices, sampling is undertaken for more than one season because of possible significant temporal variations in biotic indices’ values at the same site. It is also considered equally important that stream managers do not limit the number of habitats sampled to one. The capability the biotic indices demonstrated in measuring the health of streams used in conjunction with additional indicators based on other ecosystem elements (e.g. fish, turtles, diatoms etc) may assist river planners in assessing the most appropriate cease-to-pump (CTP) for the proposed Water Sharing Plan for the study creeks and other tributaries of the Wilsons River.</p>

The spatiotemporal pattern of macroinvertebrate community composition in two subtropical streams in north-eastern NSW, Australia

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The spatiotemporal pattern of macroinvertebrate community composition in two subtropical streams in north-eastern NSW, Australia

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