Nutrients, periphyton and macroinvertebrates were sampled every two months
for one year to assess the effects of treated sewage effluent on the Thredbo River
and to compare changes in chemical concentrations and the invertebrate
community since the introduction of nutrient removal on the Thredbo sewage
treatment plant. Chemically, the impact of the effluent was minor and was
reduced from levels measured before the addition of nutrient removal to the
Thredbo sewage treatment plant. However, the reduction may be the result of
higher flows during the study period. Biologically there was no indication of
nutrient enrichment during June, August and October, with differences occurring
between physically dissimilar sites irrespective of position relative to the sewage
effluent inflow. Large increases in periphyton and macroinvertebrates occurred in
December, February and April at both open sites and those downstream of the
sewage outflow. Previous studies found increases in invertebrate abundance and
richness immediately downstream of the sewage inflow, but the impact was
greater and extended further downstream than found in this study.
Strong correlations between total phosphorus and periphyton biomass and
chlorophyll-a indicate phosphorus was a limiting nutrient. Higher periphyton
biomass and chlorophyll-a at all sites during the warmer months (especially at
open sites with an even cobble substratum), throughout the year, indicates light,
temperature and substratum type were as important as phosphorus in controlling
algal growth. Low algal biomass during the high flow month of October also
indicates the importance of water velocity in controlling periphyton biomass.
The structure of the macroinvertebrate community was noticeably different at
sites downstream of the effluent discharge, with the exception of the most
downstream site, when compared to the upstream sites. The occurrence of high
macroinvertebrate numbers and species richness at sites with high periphyton
growth and the strong positive correlation between invertebrate grazers and
periphyton measurements shows a dependent relationship between invertebrates
and periphyton growth. Therefore, the physical factors of light, temperature and
substratum characteristics of particular sites in the Thredbo River, may be as
important in controlling the benthic community as the levels of nutrient inputs
from sewage.
| Identifer | oai:union.ndltd.org:ADTP/219394 |
| Date | January 1992 |
| Creators | Thurtell, Lisa, n/a |
| Publisher | University of Canberra. Resource & Environmental Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Lisa Thurtell |
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