Flood Plain Lower Ringarooma River Ramsar site Ecological Character Description March 2012 Blank page Citation

1.9Conceptual Models of the Site

1.9.1Overview Model

The key features of Figure 18 include the river within its Flood Plain, surrounded by heathland and marshes, breaking out of its channel at some points and discharging into lagoons, before reaching the estuary near the dune barrier. Where the river reaches the area of estuarine influence, the channel widens and is bounded by a saltmarsh on part of its northern bank before reaching a developing central basin and discharging over the delta into Ringarooma Bay. More specific conceptual models are presented for the estuary zone (Figure 19); for the coastal zone (Figure 20) and for the freshwater river, Flood Plain and wetland zone (Figure 21).

The generalised conceptual model displays the basic components and processes of the system. The major wetland systems of the estuary, seasonal wetlands, permanent wetlands, wetland forest and the river itself are integrated by freshwater inflow. Sediment inflow also arrives from upstream due to natural catchment processes and also due to historical mining activities. There are also irrigated agriculture activities adjacent to the freshwater river, Flood Plain and wetland zone which continue to change the vegetation, due to grazing and direct irrigation of the grasslands as well as water quality changes due to sediment and nutrient run-off.

The estuary is maintained by the freshwater inflows from upstream which provide habitat for a diverse estuarine ecosystem. The natural process of stream inflows and water mixing results in a salinity gradient from the upstream extent of the estuary (near the dune barrier) where it is relatively fresh, to the river’s mouth where it is close to sea water salinities. The salinity gradient changes (in position and extent) with tides and periods of large river flows. Wave action, erosion and water and sediment exchange at the River’s mouth maintains a dynamic estuary.

The models shown in subsequent sections display the components of the systems, focusing on the key features of relevance to Ramsar listing and the environmental components that influence them.

1.9.2Conceptual Model for the Coastal Zone

Although there is little information on the site’s coastal geomorphology, information presented earlier (Section 3.1) highlights the importance of sediment supply from Bass Strait, as source material for the north-east coast of Tasmania. Coastal geomorphic processes that contribute to the existing landforms include: wave wash depositing greater volumes of sand than it removes as backwash thereby providing the sandy beach; longshore drift of sand creating the sandy spit barrier at the mouth of the Ringarooma and Boobyalla Rivers; and the combination of wind and wave action that encourages dune formation behind the beach front.

The little tern, hooded plover, fairy tern, pied oystercatcher and red-capped plover nest in this zone and would use the area of the sandy beaches above the highest water line. Below the high water mark, the wetted beach, shallows, and any rocky reefs would be used for foraging by several species, including ruddy turnstone, red-necked stint and possibly greenshank. These species all prey on invertebrates and their larvae, including insects, annelids, crustaceans, molluscs and gastropods. Although the little tern and fairy tern feed mostly on fish, they would also use the sandy beach for foraging and/or resting.

No known data has been collected on the marine fish fauna nor the invertebrate fauna of the site. However, the supply of both of these as food for the species listed above is a vital component of the site. Similarly, no known data were found for the marine water quality of the site, although it is an important component of the site as well. Water quality is unlikely to change dramatically (beyond natural variability) unless through climate change. Although the marine water of the site is beyond the site’s boundaries, it is a component of the ecosystem and therefore pertinent to its ecological character. This will be influenced by processes such as mixing, upwelling, and sediment and nutrient flux.

1.9.2.1Summary of conceptual modelling for the Ringarooma Coast

Figure 19: Processes, components and impacts within the Coastal Zone of the Ringarooma Ramsar Site.

1.9.3Conceptual Model for the Estuary

The freshwater and marine water inputs to the estuary also influence the biota through processes such as salinity fluxes, nutrient exchanges, and thermal regimes. Together these influences create the estuarine habitat, which is required for some fish species for their entire life cycle or critical stages of others. These estuarine habitats provide critical habitat for Australian grayling, Tasmanian whitebait, Tasmanian mudfish, or other Galaxias species which spawn in the estuary or depend upon the estuary for part of their life-cycle.

Sediment inputs to the estuary directly influence the biota through the provision of substrate and, when in excess, the impact of smothering. Sediment inputs also provide the material for most of the estuary landforms and, when in excess, form large depositional features such as deltas and the infilling of central basins.

Other components of the Ringarooma Estuary include the saltmarsh habitat, the avifauna (particularly waders and waterbirds), fish and macroinvertebrates. Although not listed as threatened, saltmarsh is recognised as poorly reserved in Tasmania and is an important habitat for many listed bird species. Saltmarsh requires a low energy environment for development (Kirkpatrick and Glasby 1981) and has formed within the estuary zone upstream of the direct influence of most coastal waves.

There are 41 species of waterbirds/waders at the site (Appendix 3) of which ten are listed as having state, national and/or international significance (and the eleven JAMBA/CAMBA/ROKAMBA/CMS-listed species). The low energy environment conducive to the development of saltmarsh also enables the formation of mudflats and sandflats within the estuary. These provide important foraging habitat for the red-necked stint and greenshank, and to a lesser extent the great egret and cattle egret. The low energy open water surface of the estuary also provides potentially valuable fishing waters for the white-bellied sea eagle.



Figure 20: Processes, components and impacts within the estuarine zone of the Ringarooma Ramsar Site.

One species of fish, Australian grayling, has national conservation significance and inhabits the estuary at critical stages of its life cycle. Also, significant fish communities including Tasmanian whitebait occur within the site’s estuary (Table 11). Although there were no data on macroinvertebrates at the site, macroinvertebrate presence is significant in estuarine habitats, as they typically form the basis of the food chain for the fish and waterbirds of the zone.

Little information was found in the literature in relation to the condition of most of these components, or the estuary in general, at the time of listing. Some information is available from a site description of the estuary which is available on the Ozcoasts website (Coastal Zone Australia Ltd 2005) and based on information gathered for the National Land and Water Audit (1998).

1.9.3.1Summary of conceptual modelling for the Ringarooma Estuary

1.9.4Conceptual Models for the Freshwater River, Flood Plain and Wetland Zone

Nutrients are critical to allow the high biological production levels of the wetlands. Sediment is deposited in the wetlands as the river breaks its banks and stream power declines into the mouths of the permanent wetlands.

The wetlands provide habitat for significant aquatic fauna such as green and gold frogs, dwarf galaxiids, macroinvertebrates species and a wide diversity of aquatic vegetation including swamp forests.

Ecological processes within the wetlands, such as organic decay and photosynthesis from the extensive aquatic macrophytes providing valuable oxygen flux and nutrient cycling, underpin the biological production of the wetlands. Mixing and sediment release from flow and wind driven events resuspend and release nutrients and sediments to be more available. The sediment/water interface is also active in storing and releasing nutrients under different water quality conditions and under low dissolved oxygen conditions can result in phosphorous flux into the water column. In excess, this process can also cause impacts by promoting algal bloom development.

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  potential palaeobotanical and palaeofaunal remains on the site
  
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  geological diversity, including deflation hollows, lunettes, and a dune barred lake (Bowlers Lagoon)
  
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  an abundance of the Australasian shoveler (Anas rhynchotis)
  
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  11 migratory bird species listed under JAMBA, CAMBA, ROKAMBA, and/or CMS
  
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  154 taxa of native plants and 71 indigenous bird species
  
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  providing significant wetland habitat and
  
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  threatened ecological communities, including 4 species of threatened flora, seven species of threatened fauna and 3 threatened ecological communities.
  

1.9.4.1Summary of conceptual modelling for the Freshwater River, Flood Plain and Wetland Zone