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Basslink Monitoring Program Field Report : Gordon River Macroinvertebrates. Spring and Autumn Report 2006/07


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Davies, PE ORCID: 0000-0003-2651-4061 and Cook, LSJ 2007 , Basslink Monitoring Program Field Report : Gordon River Macroinvertebrates. Spring and Autumn Report 2006/07.

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Macroinvertebrates were sampled in spring (October) 2006 and autumn (March) 2007 at nine sites in the Gordon River between the Gordon power station and the Franklin River junction. Six reference sites were again sampled in the Franklin, Denison, Maxwell and Jane Rivers. Sampling was conducted as required under the Basslink Monitoring Program, with all sites sampled using:
- Quantitative surber samplers with 10 sample units taken per site placed randomly in mid-riffle habitats;
- Rapid bioassessment (RBA) kick sampling, with live-picking on-site.
The former samples were used to generate data on key metrics of abundance of taxa, total abundances and diversity (as number of taxa), both at family level and at species level for the aquatic insect orders Ephemeroptera, Plecoptera and Trichoptera (EPT). RBA samples were used to derive O/E values for each site, using the single season models developed by Davies (unpub. rep.) for Tasmanian Hydro catchments.
Patterns and trends in benthic macroinvertebrate metric values were broadly similar to those observed in the four years pre-Basslink with the following exceptions:
- Total abundance and diversity were frequently lower than pre-Basslink means, though falling within historical ranges, and sometimes accompanied by reductions in reference sites;
- Community compositional similarity between Gordon and reference sites was reduced in autumn 2007compared with pre-Basslink period, mainly due to poor sample quality following heavy rains and rising river levels.
Trigger values were generally complied with, with the exception of:
- Density of EPT species being elevated and high in the vicinity of the Denison junction. This is due to high densities of the caddis Asmicridea, which may be enhanced by the maintenance of environmental baseflows.
- Bray Curtis similarities being low in the lower Gordon due to sampling problems cited above.
A watching brief is recommended on the number of EPT species an total abundances, which while triggers were complied with, were consistently low and close to the lower trigger values fro all or most sites, especially in autumn 2007. This may or may not be a Basslink effect, and more observations are required to assess whether this is a consistent observation in years2 and 4 post-Basslink.
Data collected in this survey form part of the database used to assess changes in instream conditions associated with changes in flow regimes resulting from Basslink.
Overall, for benthic macroinvertebrates, no major changes in communities of the Gordon were observed that could be attributed to Basslink operations, and post-Basslink conditions were broadly associated with compliance with established triggers.

Item Type: Report (Technical Report)
Authors/Creators:Davies, PE and Cook, LSJ
Keywords: Tasmania, streams, freshwater, biota, macroinvertebrates, hydro, Basslink, Gordon River, Franklin River, power station
Publisher: Freshwater Systems
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