Predicting the effects of restoring tidal connectivity on the vegetation of fresh and oligohaline wetlands: Clarence River floodplain, northern NSW

Johns, Caitlin (2009). Predicting the effects of restoring tidal connectivity on the vegetation of fresh and oligohaline wetlands: Clarence River floodplain, northern NSW PhD Thesis, Ecosystem Management / Botany, The University of New England.

Author Johns, Caitlin
Thesis Title Predicting the effects of restoring tidal connectivity on the vegetation of fresh and oligohaline wetlands: Clarence River floodplain, northern NSW
School, Centre or Institute Ecosystem Management / Botany
Institution The University of New England
Publication date 2009-08-01
Thesis type PhD Thesis
Supervisor Dorothy Bell
Darren Ryder
Glenda Vaughton
Total pages 211
Total colour pages 15
Total black and white pages 196
Language eng
Subjects 060204 Freshwater Ecology
060205 Marine and Estuarine Ecology (incl. Marine Ichthyology)
050205 Environmental Management
Abstract/Summary Tidal wetlands are decreasing in number and extent worldwide due to the effects of drains and tidal barriers. These disrupt salinity gradients, reduce the depth, duration and frequency of inundation, prevent exchange of organic and inorganic materials, and interrupt movement of aquatic biota and propagules. Common effects include reductions in bird and fish populations, invasion by terrestrial and freshwater macrophytes, sediment subsidence caused by peat degradation, and activation of acid sulfate soils leading to land degradation and water quality problems. Active management of floodgates has been proposed to restore tidal exchange to waterways and wetlands of the Clarence River floodplain, on the north coast of New South Wales, Australia. Predicting the potential effects of tidal restoration on macrophyte communities is of high priority, particularly for wetlands in the fresher half of the estuarine salinity gradient. The vegetation at these sites provides important foraging and nesting habitat for rare waterbirds and a valuable pasture resource. Our ability to predict the effects of increased tidal connectivity on macrophyte communities in these wetlands is limited. Previous research in Australia has focused on saltmarsh species found in saline habitats and few data are available on the salinity and inundation tolerance ranges of macrophytes found further upstream. Existing models for predicting the effects of tidal restoration on macrophyte community composition are generally inapplicable to these communities because of the need for reference data, either from natural tidal wetlands located nearby or from surveys carried out at rehabilitation sites prior to drainage and tidal restriction. Neither of these are available for wetlands on the Clarence River floodplain. An extensive survey was used to determine distributions of macrophyte species in floodgate-affected wetlands along the Clarence River floodplain, and to relate these distributions to environmental variables, including salinity, relative elevation, acidity, water management and grazing intensity. Strong significant correlations were found between community composition and both site salinity and water depth, indicating the were identified that were both abundant and widely distributed across a range of salinities and depths, including Bacopa monnieri (L.) Pennell, Bolboschoenus caldwellii (V. J. Cook) Soják, Cynodon dactylon (L.) Pers, Eleocharis equisetina C. Presl and Paspalum distichum L.. Two tub experiments were used to demonstrate differences in the salinity and inundation tolerance ranges of focal species, the first testing the impact of salinity alone and the second the impacts of both increasing depth and salinity. The inundation tolerance thresholds of all species decreased with increasing salinity although tolerance to salinity and inundation varied considerably between species. For example, based on survivorship C. dactylon was least tolerant of high salinity in waterlogged conditions, while P. distichum was most tolerant, and when submerged E. equisetina and P. distichum grew rapidly to the water surface, while C. dactylon did not. Finally, a broadly applicable conceptual model is described for predicting the effects of tidal flow manipulation on the persistence of focal species at rehabilitation sites. This model incorporates state and transition models into an overarching assembly rule model framework, and can be applied using experimental data on species salinity and inundation tolerance ranges and field data on site conditions. A specific model was then developed for focal species at a number of sites on the Clarence River floodplain, and predictions were made about the effects of floodgate manipulation on the persistence of 13 different species. The actual and predicted distributions of seven of these species were then compared. Five of the seven species were found at sites predicted to be too saline for their survival, indicating a need for further model refinement. The conceptual model framework and data collection methods employed here are not site- or species-specific, and could potentially be used in other projects where managers wish to predict the effects of tidal flow restoration on macrophyte communities. Unlike previous tidal restoration models, this type of model is not dependent on community composition data from reference sites or historical sources, which are often not available in extensively modified areas.
Keyword Wetlands
Ecosystem management
Plant ecology

 
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Created: Tue, 10 Dec 2013, 15:04:56 EST by Caitlin Johns on behalf of Centre For Mined Land Rehabilitation