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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 2007 , Basslink Monitoring Program: Field Report Downstream Poatina: Macrophytes, Macroinvertebrates, and Mussels..

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Monitoring of macrophytes, macroinvertebrates was conducted in spring 2006 and autumn 2007, and for mussels in autumn 2007, under the Basslink Monitoring Program.
Macrophytes were surveyed in October-November 2006 and April 2007 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 and 1999/00, and in the formal pre-Basslink period (2001/02 - 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 impaired band in Brumbys Ck, as well as in the reference site Westons Ck, the latter indicating an impact, probably due to dry conditions;
- macroinvertebrate O/E values for 2006/07 falling in the range observed in 2001/02 - 2005/06 in Brumbys Creek.
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, and in 2001/02 to 2005/06;
- Sites upstream and downstream of Brumbys Creek had highly different macroinvertebrate community composition, as in 2001/02 to 2005/06;
- The number of macroinvertebrate taxa in edges upstream of Brumbys Creek had increased from 2005/06, indicating recovery from the impacts of the 2005 Blackman River dam breach.
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 were at levels observed in previous surveys. The absence of new recruits (< 75mm shell size) indicates that a spawning and settlement event had not occurred in 2006.
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.
This document constitutes the autumn 2007 Poatina Basslink field report. Formal analyses of pre- vs post-Basslink differences, trigger compliance etc have not been conducted to date. More detailed analysis of plant and macroinvertebrate community data to establish trends and changes during the post-Basslink period may be warranted once a formal reporting mechanism for assessing Basslink compliance against triggers for the Brumbys Ck – lower Macquarie system is established. Such an analysis could be used to assess the likely effects of the Poatina re-regulation weir.

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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