From fresh to saline: a comparison of zooplankton and plant communities developing under a gradient of salinity with communities developing under constant salinity levels
Daryl L. Nielsen A B D , Margaret A. Brock B C , Matthew Vogel A and Rochelle Petrie AA Murray-Darling Freshwater Research Centre, Wodonga, Vic. 3690, Australia.
B Co-operative Research Centre for Freshwater Ecology, Canberra, ACT 2601, Australia.
C Environmental and Rural Sciences, University of New England, Armidale, NSW 2351, Australia.
D Corresponding author. Email: daryl.nielsen@csiro.au
Marine and Freshwater Research 59(7) 549-559 https://doi.org/10.1071/MF07166
Submitted: 20 September 2007 Accepted: 9 April 2008 Published: 24 July 2008
Abstract
In Australia, many freshwater wetlands are becoming saline. Knowing which elements of a biotic community will persist as wetlands turn saline is relevant to their future management. We simulated gradual and sudden increases in salinity in outdoor mesocosms to test the hypotheses that: (1) aquatic plant and zooplankton communities exposed to a gradient of increasing salinity over time would initially resemble freshwater communities, but as the salinity increased they would resemble communities found in more saline systems; and (2) that a gradual change in salinity over 6 months influences zooplankton and plant communities in the same way as a sudden salinity change. Below 1000 mg L–1, as salinity increased gradually, communities rich in species and numbers of individuals resembled freshwater communities. However, as the salinity exceeded 1000 mg L–1, taxa were progressively lost and communities became less diverse. When salinities exceeded 3000 mg L–1 the diversity decreased rapidly and few taxa remained at 5000 mg L–1. Both sudden and gradual increases in salinity induced similar decreases in diversity. We predict that as natural wetlands become more saline, few freshwater biota will survive once the salinity exceeds 5000 mg L–1. In the long term, such salinised wetlands would need to be recolonised by salt-tolerant taxa for a functional wetland to persist.
Acknowledgements
We acknowledge the financial and facility support of the Co-operative Research Centre for Freshwater Ecology and the Murray-Darling Freshwater Research Centre (MDFRC) in the conducting of this research project. The experiments took place while MAB was employed by the NSW Department of Natural Resources whose functions from 2007 were incorporated into The NSW Department of Climate Change and Conservation. The mesocosm experiments were conducted at the Wonga Wetlands, an Albury Council facility. We thank Paul Wettin and Bruce Cooper for helping to define the management questions that our research aims to address. We would also like to acknowledge the assistance provided by Peter McClellan (Bluelight Lagoon, Macquarie Marshes) in collecting the sediment and to thank Dr Gavin Rees and the salinity project team for their assistance in the setting up and operation of this project and members of the MDFRC writers group for their comments on this manuscript. We also thank Dr Bob Clarke from Plymouth Marine Laboratories for advice and assistance with the multivariate analysis.
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