Occurrence of freshwater macrophytes in the catchments of the Parramatta River, Lane Cove River and Middle Harbour Creek, 2007 – 2008.
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The distribution of the freshwater plants of NSW has been little studied, and a rigorous methodology by which to undertake such a task was not previously available. This project, funded by the NSW Department of Primary Industries and Sydney Metropolitan Catchment Management Authority, adapted techniques used to determine the cover of estuarine plants for the purpose of assessing the cover of freshwater plants. The study site was done in three arms of the Sydney Harbour catchment Middle Harbour Creek, Lane Cove River and the upstream part of Parramatta River. These arms and their tributaries were explored extensively by foot to provide an indication of the extent and complexity of the drainage system and to determine the extent of fieldwork needed to map the in-stream vegetation.
The project was initially hampered by a lack of accuracy in existing digital and printed maps. It was found that many small tributaries were not shown on standard maps. For example, one map showed 17 tributaries entering Middle Harbour Creek, but examination of other maps and field inspection revealed 47 small creeks flowing into this major arm of Sydney Harbour. Similar situations prevailed for the Lane Cove River and, to a lesser extent, for the Upper Parramatta River. A major output from this project, therefore, was the construction of an accurate stream network. This new network will be of use in future monitoring and in prioritising areas for weed eradication.
Three hundred and eighty six sites were inspected and the presence of freshwater aquatic vegetation was noted and categorised at each site as submerged, emergent, or floating, and then differentiated as being either native or alien (i.e., weeds). Records were also made of the underlying streambed, water flow and turbidity at each site. The presence of aquatic weeds was surprisingly low, but it is recommended that steps be taken to eradicate them before the problem gets too difficult to control.