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

Detailed Description of the Site

1.1Setting

The mid to upper catchment is described as “humid cool/cold mountain ranges situated in Tasmania's inland north-east. The mountains are capped by Jurassic dolerite with shallow gradational soils. Silurian-Devonian siltstones and mudstones covered with gradational soils constitute a substantial part of the lower hills. Lowland vegetation comprising mainly open sclerophyll woodlands and heath while the upper slopes consist of wet sclerophyll forests, some rainforest and alpine vegetation in the highest regions. Land use: forestry, mining and agriculture (grazing)” (Environment Australia 2000).

The lower to mid catchment is described as “moist and dry subhumid warm coastal plains. Devonian granites dominate the elevated areas of the subregion forming low rugged ranges. These are overlain by shallow stony/gravelly gradational or duplex soils carrying Eucalyptus amygdalina open forest and woodland with open heath on higher peaks. Quaternary/Tertiary materials overlain by deep sandy soils typify extensive lowland plains, coastal deposits and dunes. Coastal plains have been heavily modified by agriculture (grazing)” (Environment Australia 2000).

The catchment covers an area of approximately 975 square kilometres (NWC 2009 and Figure 1). At its lower end, the catchment encompasses the site, which lies on the sandy flood plain and contains extensive marshlands including Fosters Marshes and a number of shallow lagoons including Rushy Lagoon, Shantys Lagoon, Blueys Lagoon and Bowlers Lagoon.

The site is irregularly shaped and covers an area of 3,519 hectares. At its northern edge, the site includes the Boobyalla Inlet estuary and parts of both Boobyalla Beach and Murdochs Beach to the east and west of the River mouth respectively (Figure 2). A mobile sand dune system occurs in the northern part of the site. The site extends approximately eight kilometres north to south, encompassing a variety of habitats which are significant to a number of species.

The bulk of the wetland area is altered from its natural condition. This has resulted from large-scale sedimentation arising from mining operations in the late 1800s and early 1900s. However, the large trees on the site, as well as aerial photographs over several decades, show that many of the current conditions have been established for decades and sediment movement is no longer as dynamic as it once was. Therefore, current conditions for many of the site features are likely to be indicative of the conditions at the time of listing.

Areas that remain relatively unaffected by this mining-induced sedimentation include Bowlers Lagoon (a dune-barred lake in the sand sheet behind Boobyalla Beach) and some deflation basins (basins formed by wind blowing sediments from the site) with associated lunettes (arc-shaped mounds formed on the lee side of deflation basins, made up of deposited sediment blown from the deflation basin).

The sediment load of the Ringarooma River was estimated to include 40 million cubic metres of mine tailings since the late nineteenth century (Knighton 1991). Some of this sediment has been transported to the Ramsar site, where it has been deposited to form a huge and complex set of levees and sediment splays. These trap water on the Flood Plain, forming extensive wetlands that have evolved and migrated for approximately 100 years (Jerie and Houshold 2001). As a result, the placement and evolution of biological communities and habitats featured in the site reflect anthropogenic influences. Further, much of this mining-derived sediment remains upstream of the site and is predicted to be transported to the site, further changing its character, including the nature and location of the wetlands (Jerie and Houshold 2001).

However, it is likely that many of the habitat and community types present today and at the time of listing were present at the site prior to mining impacts. As geomorphic processes fill in depressions at one location and create new ones elsewhere on the site, wetland vegetation shifts, creating a mosaic of community types, with differing ages and attributes. This dynamic nature of the vegetation is a common feature of Flood Plain wetlands and it is likely that the rapid input of the mining sediment increased the rate of change rather than completely changing the direction of the wetland’s evolution.

There is potential for new releases of mining-derived sediment, with a former mine soon to re-open at a site north of the Ringarooma River near Gladstone. This mine - the Scotia Mine - is situated on Newhaven Creek, a tributary which enters the Ringarooma River downstream of Gladstone. Further, the majority of the Ramsar site itself is covered by mining tenements, which extend beyond the site and out into Ringarooma Bay. These are discussed further in the threats section (Section 4).

Figure 1: Ringarooma catchment, showing location within Tasmania.

Figure 2: Boundary of Ramsar site displaying lagoons and marshes.

The mining-derived silt and sand from the river catchment overlies flat plains of Quaternary clays, sands and gravels. Silty clay soil overlays a deep grey sand, with silt content decreasing with depth. The area is regularly flooded by overflow from the river. The maximum depth of water in The Chimneys is between two and four metres, and its maximum depth of permanent water is between half a metre and one metre. The 2005 RIS notes that water pH in the wetland is around five, although the source of this data is not cited.

The hydrology of this site is influenced by tidal flows and river flows. Local groundwater also influences the site’s hydrology, particularly in areas that are separate from the river, such as Bowlers Lagoon, (Jerie, personal communication). In particular, water that is discharged from the Ringarooma River during flood events is prevented from re-entering the river channel due to the presence of natural levees adjacent to the channels. The trapped water maintains the surface water of the nearby wetlands and also replenishes the local groundwater, thereby sustaining more distant wetlands, such as Bowlers Lagoon. Most of the wetland is above the tidal limit and is mostly influenced by inflows from the Ringarooma River. The hydrology is also influenced by mining-related sediment deposition and water trapping described above. The estuary mouth is open and therefore the estuary experiences tides.