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

1.12Threats to the Freshwater Zone

Within the setting provided by the Ringarooma catchment, the key threatening processes to these components can be separated into direct and indirect threats (Figure 23). The direct threats include:

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  the impacts of sedimentation, particularly through the progression of the fine sands generated by past mining practices
  
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  damage to the wetland soil/sediment structure through stock trampling
  
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  inputs of excess nutrients through grazing and dairy wastes
  
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  loss of threatened vegetation communities (including weed invasions), via stock grazing and pasture management practices
  
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  changes to the hydrologic regime via:
  
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    local (water extraction)
    
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    regional/global (climate change) impacts and/or
    
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    lowering of the stream bed.
    

The sand deposition dominates the channel environment from upstream of the Ramsar site to the mouth of the Ringarooma River. This sedimentation has been evident for decades. Examination of the maps and aerial photographs in Jerie and Houshold (2001) shows that the quantity and location of the sediment has changed markedly since the earliest aerial photographs were taken in 1949 (Figure 24). This has had an impact on the depth of sediments dammed by the river levee and the area of dammed water (Jerie, personal communication). For example, the 1964 aerial photograph (red circle in Figure 25) shows a large area of standing water to the west of the original channel, north of Shantys Lagoon. By 1978, this waterbody had been substantially filled in with sand (indicated by the red circle in Figure 26). However, this process of sediment movement does not necessarily lead to a loss of wetland, with some wetland types changing to other wetland types. For example, comparison of the 1978 (Figure 26) and 1999 (Figure 27) aerial photographs shows that a considerable part of Shantys Lagoon has been altered and changed over the 21 year period from bare sand to coast paperbark swamp forest (indicated by the green circles in the photographs).

The extent to which this sedimentation poses a threat to the ecological character of the site is uncertain. Recent observations (Figure 28) and photographs (supplied by Michael Propsting, neighbouring landholder and pilot) indicate a minor change in the area of sedimentation after a recent period of flow (early June 2007). A review of the flow records show these were equivalent to an annual flow event (Chris Bobbi, DPIW, personal communication). If this sand splay is growing in area, or moving, it is likely to be only occurring during much larger and less frequent flow events.

The present geomorphic rate of change (sedimentation rate) presents itself as a significant knowledge gap. Similarly, the length of time before the sedimentation regime is likely to change to an erosion regime, and the form that erosion may take, is also a significant knowledge gap. Further, the rate and extent of change from one wetland type to another over time is unknown.

The input of sediment through current and future mining, vegetation clearance and grazing practices also has the potential to exacerbate the impacts. Management of the sedimentation threat will require detailed consideration and clarification of management objectives. A key issue to resolve will be whether to allow the upstream sediment that is already in the system to ‘run its course’ regardless of impacts on the wetland system, or whether active management of the site will be undertaken. This analysis of objectives is required prior to the development of management plans.

Over a longer period of time (several decades) the cessation of sedimentation and the onset of channel degradation (that is, the sediment runs out and the Ringarooma River starts picking up the previously deposited sediment, thereby cutting its channel deeper into the Flood Plain), may be a far greater threat than the current sedimentation, with channel incision potentially causing isolation, and ultimately, a drying of the wetlands.

Figure 23: Conceptual model for threats to the Ringarooma freshwater river, Flood Plain and wetland zone.

Figure 24: Aerial Photograph of the Lower Ringarooma Flood Plain, 1949 (Source: Jerie and Houshold 2001; base images produced by Tasmap DPIW).

Figure 25: Aerial Photograph of the Lower Ringarooma Flood Plain, 1964 (Source: Jerie and Houshold 2001; base images produced by Tasmap DPIW). The red circle marks the location of the wetland later filled by sand.

Figure 28: Sand encroachment at the entrance to a permanent wetland (Shantys Lagoon, Ringarooma Ramsar Site; photo: L.N. Lloyd, May 2007). Note vegetation stabilising sand on right hand side of photo.

The second major threat to the freshwater zone is the rapid increase in weed cover, through the expansion of grazed pasture within the site. In a site managed for conservation purposes, the increasing cover of pasture leads to the loss of native vegetation communities, accompanied by the establishment of large areas of introduced grasses and other weeds. This threat is particularly large as it has already encroached onto a substantial part of the site (see Section 6 for discussion of changes in ecological character to the site). At the time of listing, a large part of the site was rough grazed, including Fosters Marsh in the centre of the site (labelled ‘Agricultural Land” in Figure 10) and the south-eastern area of the site (also labelled ‘Agricultural Land” in Figure 10).The spread of weeds is exacerbated by the grazing cattle, with seeds often attaching to the cattle hair and being transported to new areas.

The south-eastern pasture area of the site has changed since listing, from rough grazed to pivot irrigation. Figure 26 (taken approximately four years before listing of the site in 1978) and Figure 27 (taken approximately 17 years after listing in 1999) show the change from rough grazed pasture to irrigated pasture. Although the irrigated land was already designated as agricultural land, further expansion of the irrigation would encroach into the more natural areas of the site and must be considered a serious threat to the site. In contrast to the south-eastern part of the site, the previously grazed Fosters Marsh has subsequently had cattle removed and is now being regenerated.

There is also the threat of weed incursion (e.g. Salix sp.) from materials distributed downstream from higher in the catchment. Although gorse has been controlled by substantial on-ground work, the remaining seed bank is an ongoing threat.

The dairying activities within and adjacent to the site also pose a threat to water quality. Rushy Pastoral currently leases three commercial dairies in the Rushy Lagoon property. These dairies are located to the south of the Ramsar site, and together comprise approximately 760 hectares, or 22 percent, of the site (GHD 2008). Although the dairying operations are not on the Ramsar site, the dairies have the potential to impact the health and status of the site through high nutrient waste discharge. However, the development of management plans for the property (Sherriff 2007; AAS & BIS 2007) and the Ramsar site (GHD 2008) should mean that if these activities have been contributing nutrients to the site, they should be reduced into the future.

Inputs of elevated nutrient concentrations to the freshwater zone have the potential to turn the site eutrophic, leading to algal blooms and oxygen deficits in the water column, with potentially sever impacts on the aquatic fauna. The most likely source of nutrients comes from cattle faecal inputs through grazing, particularly grazing of improved pasture by dairy cattle. In particular, the irrigation of improved pasture provides a mechanism for washing the faecal material into drainage lines. Any discharges from dairying activities would also pose a threat to the site. Read and Graham (2000) note: “The majority of the wetlands are surrounded by woodland used for rough grazing until 1998 although certain areas have been subject to draining. Recently, the area surrounding the wetland has been developed extensively for dairying. One of the major threats to the wetland is the establishment of pasture in close proximity to the wetland perimeter. This may pose a serious threat to the ecological health of the wetland in terms of enrichment via sedimentation and nutrient runoff from surrounding pasture and dairy practices”. Effective management of the Ramsar site must include buffer zones and clear directions on acceptable limits of on-site and off-site impacts from dairying and rough (unimproved pasture) grazing.

Potential threats to water quality not presented in processes, components and impacts within the freshwater zone (Figure 23) but still worthy of investigation, include: the use of biocides and other chemicals in forestry and agriculture within the catchment; and current/future mining impacts. Some of these potential impacts may be measurable in the waters of the Ringarooma River at Gladstone. Others may occur in tributaries that enter the Ringarooma River downstream of Gladstone, and may need to be assessed at the point of input and also closer to the Ramsar site.

One particular concern is the potential for pulse impacts, through short-term agricultural spraying events or mine waste spills, where routine (for example monthly) water monitoring may not register any impacts. These types of threats require biological monitoring, to assess impacts on the biota that may be missed by routine water chemistry sampling. This approach of highlighting key threats and their potential impacts is termed a ‘risk-based approach’ and is advocated by ANZECC & ARMCANZ (2000).

Grazing also poses significant threats to the freshwater zone through direct trampling damaging the wetland substrate. Trampling of wetland substrate can lead to desiccation in drier weather and the formation of eroding drainage lines during storm events.

Hydrologic changes also pose a significant threat to the freshwater zone. Currently water extractions and river regulation are not a significant issue and the primary focus for these should be to maintain extractions at an acceptable volume. Similarly, any proposed dams anywhere within the catchment of the Ringarooma River or its tributaries should undergo detailed assessment to determine possible impacts on water delivery to the site, including dams for mining and dairying.

Climate change is the main factor that possibly threatens the hydrology of the wetlands but its impacts on rainfall are not predictable with any certainty. The predicted rise in sea level (of up to one metre over the next 50 -100 years) is likely to have a significant impact on many coastal wetlands from marine incursions, increased erosion and storm surge damage (Sharples 2006; DPIPWE 2010; Grose et al. 2010). Sea level rises of one metre at the Ringarooma/Boobyalla estuary would likely result in significant incursions of marine waters into the freshwater wetland zone as these are currently protected from seawater incursions by a low, one metre high natural barrier which is rarely overtopped by marine waters (Bobbi, personal communication). If significant incursion of marine waters into the wetlands did occur, it may arguably lead to large-scale death of the extant vegetation, with subsequent ramifications for habitat, fauna and geomorphology. Similar to the issue of sedimentation, management components and attitudes towards intervention and direct management action will need to be determined before specific management plans can be developed.

Similar to the key threats to the Ringarooma Estuary, other threats have been identified for the freshwater zone that must be considered and evaluated as part of future management plans for the site. These include:

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  drainage of the wetland from agricultural activities (either intentionally or through stock tracks creating linear depressions that form drainage lines)
  
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  loss of habitat and vegetation communities through land clearance
  
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  damage to riparian condition in the Flood Plain through agricultural activities, including stock access
  
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  impacts of increased sediment deposition through future land uses, including land clearance in the catchment and new mines
  
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  drainage of wetland over the long-term, accompanying a shift from an aggradation regime to a degradation regime in the Ringarooma River
  
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  declines in water quality through forestry activities upstream, including use of biocides and other chemicals (discussed above)
  
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  declines in water quality through mining impacts, including spills of chemicals and discharges other than sediment
  
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  introduction of weeds and pest animals through grazing on and near the site and also through on-site dwellings
  
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  changes in hydrologic regime through climate change
  
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  changes to hydrologic regime through increased water extraction
  
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  damage to habitat and vegetation communities through human access and illegal recreation activities (for example trail and quad bikes) and
  
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  loss of habitat and vegetation communities through gravel extraction.