Flood Plain Lower Ringarooma River Ramsar site Ecological Character Description March 2012 Blank page Citation
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kEY ACTUAL OR POTENTIAL THREATS TO THE SITEFrom discussions with local landholders and the project Steering Committee, and through review of relevant documents, the drivers of major actual and likely threats were determined. The threats to the estuary zone and freshwater zone are discussed separately, as there are several significant differences in the types and extent of threats between the two zones. 1.10Threats to the Coastal ZoneApart from potential climate change and associated sea level rises, there are few human derived threats to the coastal zone. Impacts of recreation currently appear minor. There is no apparent indication of increasing recreational activity, although there are no data on recreation at the site. The potential impacts of climate change are discussed in association with the estuary zone in Section 4.2 (below). 1.11Threats to the Estuary ZoneThe key components of the estuary zone (discussed in Section 3.5.2) are the wetland habitat types (saltmarsh, intertidal mud and sand flats, estuarine waters, and coastal lagoons); the avifauna (particularly shorebirds/waders and water birds), migratory and rare fish; and fish and macroinvertebrates (as food). Major threats to these components exist through potential impacts on key site components. The major direct threats to the Ringarooma Estuary were identified as:
These are presented in Figure 22. Excessive inputs of sediment from past mining have already occurred in the site’s estuary zone (for example Jerie and Houshold 2001), causing infilling of the formerly deep channel at the Port of Boobyalla. Data suggest that the high level of sedimentation at the site is likely to persist for decades (Knighton 1991) although the effects on the site in general - and the estuary zone in particular - are difficult to predict. It is possible that much of the remaining sediment may not reach the estuary zone, being trapped within the freshwater zone of the site (Jerie and Houshold 2001). Similarly, the threat of dairying directly impacting on the water quality of the estuary zone is difficult to assess, as the water and suspended sediment pass through the freshwater zone prior to reaching the estuary zone. If the freshwater zone provides a filtering mechanism, retaining many of the nutrient-carrying particles and also absorbing many of the bio-available nutrients, the threat to the estuary zone may be small. The difficulty in predicting the impacts of both the mining sediment and the dairy-affected water quality on the estuary zone represents an important knowledge gap. The recent development of management plans for the property (Sherriff 2007; AAS and BIS 2007) and the Ramsar site (GHD 2007) has meant that threats from these impacts should reduce into the future. Further discussion of these two threats is presented in the section on threats to the freshwater zone (Section 4.3), as the threats are likely to be greater in that zone. There are also potential impacts from stock access to the riparian zone of the estuary, with private leasehold on land right up to the water (Figure 5) and close to areas of saltmarsh (compare Figure 5 and Figure 10). With the exception of potential climate change impacts on delivery of rainfall, the main changes to hydrology within the Ringarooma Estuary are likely to be a result of geomorphic changes, unless water extractions increase. Current extractions of water in the lower catchment are only a small percentage of total discharge in the summer low flow season (which is also the peak extraction season) and much of the water extracted in the upper catchment is returned to the stream system (Read and Graham 2000). However, substantial increases in water extraction or stream regulation (dam building) could significantly alter the balance of freshwater and marine water causing shifts in the habitat and vegetation communities. In addition, reduced water availability may result in reduced flushing of sediment in the system. A potentially major impact on the site is a possible predicted rise in sea levels accompanying global warming. As discussed earlier, an incursion of the marine waters beyond the current limit of estuarine influence could severely impact the ecological character of the site. Apart from drowning the existing saltmarsh community if sea rises are significant, increased depths would impact on many of the existing geomorphic features and processes, through inundation of the site and beach translation. This includes impacts upon the maintenance of the barrier, and the morphology of the delta and the channel. Although there is little that can be done at the site or regional scale in terms of reducing rising sea level, there are management options that can be taken to reduce the impacts of rising sea level, including vegetation protection and management, and revegetation.
Figure 22: Conceptual model for threats to the estuary zone of the site. |