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Basslink Monitoring Program: Field Report Downstream Poatina: Macrophytes, Macroinvertebrates, and Mussels.


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Davies, PE ORCID: 0000-0003-2651-4061 and Cook, LSJ 2006 , Basslink Monitoring Program: Field Report Downstream Poatina: Macrophytes, Macroinvertebrates, and Mussels..

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Monitoring of macrophytes, macroinvertebrates was conducted in spring 2005 and autumn 2006, and for mussels in autumn 2006, under the Basslink Monitoring Program.
Macrophytes were surveyed in November 2005 and May 2006 at six sites in Brumbys Creek and ten sites in the lower Macquarie River (five upstream and five downstream of Brumbys Creek). A survey was conducted in each season, as required under the Basslink Monitoring Program, with all sites surveyed using:
- Boat-operated viewers, assessing % cover of dominant macrophytes at 2-5 m intervals across established, fixed transects in Brumbys Creek weirs 1 and 3;
- 1 x 1 m quadrats, spaced at 1m intervals from an arbitrary head peg on transects across the channel edge in the lower Macquarie River, assessing % cover of dominant macrophytes.
Macroinvertebrates were sampled in Brumbys Creek, Westons Creek, and the lower Macquarie River as follows:
- Quantitative surber sampling, with 10 sample units taken per site placed randomly in mid-riffle habitats, in Brumbys Creek (downstream of Weir 2) and Westons Creek (a reference site);
- Rapid bioassessment (RBA) kick sampling, with live-picking on-site in riffles at the above Brumbys and Westons Creek sites, and in edge habitats in the lower Macquarie River at three sites upstream and three sites downstream of the Brumbys Creek junction. Two RBA samples were collected at each sampling location on each sampling occasion.
The former samples were used to generate data on abundances of individual taxa, total abundances and diversity (as number of taxa) for Brumbys Creek and the Westons Creek reference. The latter samples were used to derived O/E values for each site, using the RIVPACS models developed by Davies et al. (1999) for Tasmanian Hydro catchments and the DPIWE NRHP AUSRIVAS models, as appropriate.
Patterns and trends in macrophyte and macroinvertebrate abundance and diversity and in macroinvertebrate O/E values were similar to those observed in 1995/96, 1999/00, 2001/02, 2002/03, 2003/04 and 2004/05 with:
For Brumbys Ck -
- Dominance by the same macrophyte species (Isolepis, Myriophyllum, Chara/Nitella, Potamogeton) as in all previous years of sampling, with seasonal shifts in cover;
- Number of taxa and total macroinvertebrate abundance being lower to that in Westons Creek, and with very different community composition;
- Macroinvertebrate O/E values falling in the significantly to severely impaired band in Brumbys Ck, and in the reference to above-reference band for Westons Ck;
- no significant differences between macroinvertebrate O/E values for 2005/06, 2004/05, 2003/04, 2002/03, 2001/2002 and 1995/96.
For the lower Macquarie River –
- Significant differences in dominant macrophytes between the sites upstream and downstream of Brumbys Creek, as a result of sustained differences in environmental conditions, as identified in the IIAS report for Poatina, in 2001/02, 2002/03, 2003/04 and 2004/05;
- Sites upstream and downstream of Brumbys Creek had highly different macroinvertebrate community composition, as in 2001/02, 2002/03, 2003/04 and 2004/05;
- The number of macroinvertebrate taxa in edges upstream of Brumbys Creek was severely reduced compared to previous autumns and other seasons, but with little change downstream of Brumbys Creek. This may be caused by the Blackman River dam breach in 2005.
- O/E values falling in the significantly impaired band, and with a decline upstream of Brumbys Creek relative to previous years.
Mussels were surveyed in the lower Macquarie River at seven sites downstream of Brumbys Creek. Surveys were conducted by scuba on fixed transects across the river. Mussel densities remained at levels observed in the 2002 and 2005 surveys. The presence of new recruits (< 75mm shell size) indicates that a spawning and settlement event occurred in 2005.
Data collected in this survey will form part of the database used to assess changes in instream conditions associated with changes in flow regimes resulting from Basslink.

Item Type: Report (Technical Report)
Authors/Creators:Davies, PE and Cook, LSJ
Keywords: Tasmania, streams, freshwater, hydro, Basslink, Poatina
Publisher: Freshwater Systems
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