Water quality in the Georges Catchment

Information taken from detailed scoping report. We can provide a copy to anyone interested in the

source of information provided below. References have been omitted to make this summary simpler

to read.

Georges Bay

The Bay

Georges Bay has been given a Class D rating in terms of conservation significance: o indicates that the estuary has low conservation significance, meaning that the

estuary itself and associated catchment have been moderately degraded by human impacts.

o recommended that the estuary be available for a variety of commercial and recreational purposes and remediation processes implemented where practical.

Protected Environmental Values are: o protection of aquatic ecosystems – the protection of the modified (not pristine)

ecosystems where edible fish, crustacean and shellfish are harvested, o recreational water quality and aesthetics – primary and secondary contact water

quality and aesthetic water quality o Protection of Aquaculture Species.

Complete turnover of water in the Bay is likely to occur approximately every 2-3 weeks. The exchange rate and flushing rate are about 10% less than other large Tasmanian east coast estuaries (e.g. Little Swanport, Pitt Water and Pipeclay Lagoon) mostly due to the long narrow entrance and large volume of the bay.

A report by TAFI found that based on the limited data available it has been found that the Bay is currently in relatively good health.

o Nutrient concentrations are generally low. o Algal levels are below those constituting a bloom. o No pesticides or herbicides have been found in the water or flesh of fish caught in

the Bay. o There are good populations of both seagrass and fish in the Bay.

Ecological communities

In 2005, it was reported that seagrass in Georges Bay was very abundant (688 ha) and had been for the previous 3 to 5 years. When compared to mapping done circa 1950 and circa 1990, there was substantially more seagrass in the Bay in 2005, notably in the very shallow nearshore areas. However, in some areas the abundance of seagrass may have been underestimated in studies circa 1950 and circa 1990 due to lack of access to underwater video technology

o The maximum depth of seagrass in Georges Bay in 2005 was 6.25 m along the southern shores of the bay and at McDonalds Point

o The shallower maximum depths were found in the inner harbour area (about 2.7 m) and Moulting Bay (about 3.4 m).

o Reasons for the fluctuating seagrass abundance is not clear however threats include nutrient and sediment loadings, reduced water clarity and direct disturbance.

There are a high number of recorded fish species in Georges Bay (39) which is comparable with other large Tasmanian estuaries (Tamar: 41; Derwent: 37; Great Swanport: 37; North East Estuary on Flinders Island: 40).

o The seagrass beds of Georges Bay were found to be dominated by fish fauna such as the pipefish and small leatherjackets but recreational fish species such as sand flathead, southern sea garfish and southern calamari are also present.

o The seagrass of Georges Bay supports a large variety of fish species in high numbers o Compared to other regions in temperate Australia, there are relatively few larger

fish species using the seagrass as nursery habitat. o High densities of oligochaete worms, ragworms (Family Nereididae), Paradexumine

churinga, Leptochella dubia blood worms (Family Capitellidae) and low densities of Phoronid worms were also found inhabiting seagrass beds in Georges.

Many of the preferred recreational and commercial fish species use unvegetated areas of Georges Bay for reproduction and feeding. Typical species found include flounders, hardyheads, leatherjackets, eastern Australian salmon and mullets.

o On deeper (>10 m) unvegetated soft bottomed regions typical fish found include leatherjackets, gurnards and stingrays.

o A wide variety of macroinvertebrates also inhabit unvegetated regions of the bay. o Native oysters also inhabit silty sand habitats often below the deep edges of

seagrass beds. In 1987 a survey of native Flat Oyster distribution was conducted which estimated over 24 million native flat oysters present in a series of beds covering about 33 Ha through Georges Bay. The highest quality oysters were found in and around the flood tide delta between Humbug Point and Lords Point.

Areas of conservation significance

Around Georges Bay, the St Helens Point Conservation area covers 1066 hectares of land which contains coastal heath communities and the Peron Dunes; a series of tall sand dunes up to 50 metres high which in the past have been severely degraded by foot and vehicle traffic.

Jocks Lagoon Stieglitz is a Ramsar Conservation Wetland. The Lagoon is a small shallow freshwater lagoon located on the southern side of Georges Bay and forms part of the larger Chain of Lagoons swamp and wetland reserve. The lagoon itself is 20 metres above sea level and is of significance scientifically and socially as it contains species of high conservation

significance. The lagoon is acidic with a pH of 5.5 and is the only identified freshwater site of the dinoflagellate Prorocentrum playfairi. The site is also host to a range of small sedge land and coastal communities and has two rare floral species: Baumea articulate, and Villarsia exaltara. While the land is primarily privately owned there are is a small area covered under the St Helens Point Conservation Area.

Humbug Point Nature Recreation Area; 1620 hectares of coastal heath land that has been set aside for bird watching and bush walking (Mount et al., 2005).

Medeas Cove Wildlife Sanctuary is another valued area which is a natural embayment that has been filled with silt and clay from mining operations higher in the catchment. Today the resultant vegetated mudflats support a large range of estuarine species at various life stages and the area is particularly valued for its birdlife (Mount et al., 2005).

Oysters

Georges Bay supports a substantial commercial oyster fishery.

Since 1997 Pacific Oyster farmers of Georges Bay have experienced ongoing unexplainable health problems including shell deformities, slow growth rates and mortality.

o A substantial number of unexpected mortality events have been reported as occurring after rainfall and subsequent flooding and/ or following handling procedures in spring and summer.

o Health issues in commercial oyster leases tend to occur within 2 to 6 weeks after a flood event.

All oyster leases in Georges Bay are classed as ‘Approved Conditional‘, meaning they are subject to intermittent, but predictable pollution events and have appropriate management programs to eliminate risk to the consumer.

o Closure of farms can occur when critical values of rainfall or salinity are met or exceeded and/ or when biotoxins (toxic algae) and sewage treatment malfunctions are detected.

o Re-opening of farms only occurs after Tasmanian Shellfish Quality Assurance Program (TSQAP) advise suitable conditions.

o Since 1997, it is estimated that the oyster farmers of Georges Bay lose between $20,000- $ 50,000 of stock per year. Interestingly, in Moulting Bay only oysters are regularly dying and not other molluscs or finfish and not the oysters in the lease near the barway. This suggests that the issue is specific to oysters or Moulting Bay, or both.

In December 2003, a Helicopter carrying a 29kg load of alpha cypermethrin; a biocide that is toxic to aquatic ecosystems at 4 µg/L, crashed 250 metres uphill from the South George River.

o Following this, between 27- 30 January 2004 a 100 year record rainfall of 234 mm was recorded at the St Helens Post Office and 284 mm at Pyengana in the upper catchment.

o This lead to a flooding of the St Helens township and shortly after massive mortalities (90%) of intertidal oysters and other species in Georges Bay.

o These mortalities were located 5 km downstream of the St Helens drinking water intake and contributed to a loss of $1.6 million to the oyster industry.

A report by Percival in 2004 compiled the largest collation and analysis of data associated with oyster mortality at the time. The report suggested that there was no apparent single cause of health problems of oysters in Georges Bay, rather, numerous factors that may render oysters susceptible to additional stressors like a flood event. Extended periods of low salinity, toxic phytoplankton, high turbidity affecting phytoplankton abundance, speciation and oyster feeding rates, contamination of sewage and contamination of water by forestry, industry, urban and/or agricultural chemicals were named as possible contributors.

A report by Scammell in 2004 detailed the helicopter crash in the Georges Bay Catchment prior to the flooding event and investigated the links between these events. It was argued that the amount of rainfall alone could not be responsible for the recorded mortalities of oysters as well as intertidal and sub tidal species. However, DIPIPWE presented a strong case against many of the assumptions made in the Scammell report. This included the unlikelihood of biocides entering the waterways that deliver to Georges Bay as they exhibit strong adsorption to clay particles

The George Catchment

Impacts of historic activities on the catchment

The history of mining in the Georges Bay catchment may be one of the most significant impacts on water quality and siltation of the Bay.

o Tin was discovered at the foot of the Blue Tier and the tin mining industry was established. Mining took place in the George River and Constable Creek/Golden Fleece Rivulet catchments. The most productive mine was the Anchor Mine on the

headwaters of the Groom River near Lottah which operated almost continually between 1885 and 1945.

o It has been estimated that between the mid 1880’s and 1929 when stricter controls for disposal of tailing was introduced, 1.2 million m3 of sediment was deposited on the Goshen floodplain with smaller amounts deposited at the Priory and the George River delta.

o These floodplains were choked with sediments which elevated bed level and caused increased over-bank flooding and deposition.

o The degradation of available waterways drove the tin industries decline in the Blue Tier as the water was required for the mineral refinement stage for sorting the ore. Reduced water velocities made this process slower and less effective.

o The mobile sediment produced by the mining activities is moving down the river system as a large “slug” that impacts on river flow and form. This coupled with deforestation and agricultural clearing (from the early 1900’s to the present) has contributed to sediment loads in the river and more destructive flooding as well as the development of the George Rivers over one kilometre wide multiple active braided stream system.

o After floods in 1929, many sections of Georges Bay were impacted and much of the upper reaches of the Bay were lost.

o It was estimated by 1998 that 0.4 million m3 of tailings had been discharged into Georges Bay. It is likely that there is still a considerable amount of tailings material still held in the catchment. The three major flood plains (Goshen, Priory and Delta) still all have relatively thick deposits of sediment. Furthermore, it is expected that this material will continue to enter Georges Bay for many more decades.

o While there is still a substantial amount of sediment within the George River system the channel is actively down-cutting to its original bed level. It has been suggested that while the George River appears to be self-remediating from these human impacts, the Golden Fleece Rivulet and Medeas Cove may never recover from the sediment loading.

Current land use and management impacts on water quality

It has been estimated that 83% of current diffuse sediment loads to the bay come from hillslope sources versus 17% from streambank erosion.

Almost all pollutants entering the Bay are from diffuse sources. Less than 0.5% of sediments (measured as Total Suspended Solids or TSS) and enterococci are sourced from sewage treatment plants, while 3-4% of nutrients come from these point sources.

The chart below shows the proportion of diffuse pollutants coming from different land uses for the entire Bay catchment versus the relative land use area. Dominant land uses across the catchment are native production forests and green space. Major sources of nitrogen and enterococci are grazing and dairy land uses. A greater proportion of sediments and phosphorus are sourced from native production forests, although loads are still greater for grazing and dairy relative to the area they represent in the catchment. Urban areas are not a major contributor to total loads but do contribute greater loads relative to area than many other land uses.

Proportion of area versus diffuse pollution by land use for entire Bay catchment

Subcatchments of the Georges Bay catchment

Loads in each subcatchment depend on the relative area of various land uses in each

catchment. Native production forests or green space are the dominant land uses in all

catchments except Colchis Creek which is dominated by grazing with a substantial urban

area. Grazing is also a substantial land use in the Lower and Upper George River catchments,

and to a lesser extent in the Lower Powells Rivulet, North George River and Factory Creek,

Ransom River and Southern Bay Foreshore catchments. The Southern Bay Foreshore

catchment also contains a substantial urban area.

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Relative land use areas in the Georges Bay catchment

Major sources of each of the pollutants vary by subcatchment depending on land uses and

management practices such as maintenance of riparian vegetation in each subcatchment.

o Total Nitrogen (TN) loads are dominated by those sourced off grazing areas in the

majority of catchments, except Forester creek, Higginbothams creek and Hunt Mine

creek where most TN comes from green space and native production forests. In

these cases, these two land uses make up 96%, 97% and 99% of land use area

respectively. Urban areas are a significant source of TN in Colchis creek and the

Southern Bay Foreshore catchments.

Relative land use contributions to Total Nitrogen (TN) loads by catchment

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o Total Phosphorous (TP) and Total Suspended Solids (TSS) loads are dominated by

native production forests and green space in many catchments. However in Colchis

creek and the Southern Bay Foreshore catchments, urban and grazing areas are the

major contributors of loads. Grazing is also the dominate source of TP and TSS in the

Lower Powells Rivulet, Lower George and Upper George River catchments. Grazing

areas also contribute substantial loads in the Flagstaff and Constable creek and

Golden Fleece Rivulet catchments. Dairy lands are a substantial source of TP and TSS

in the South George River, and North George River and Factory creek

subcatchments.

Relative land use contributions to Total Phosphorous loads by catchment

Relative land use contributions to Total Suspended Solids loads by catchment

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o Grazing and dairy areas are the major contributors to enterococci loads in all

catchments except Higginbothams and Hunt Mine Creeks where green space and

native production forests are the major sources respectively. These land uses

represent 97% and 74% of their total catchments areas in each case. Urban areas

also make substantial contributions to enterococci loads (over 20%) in the Colchis

Creek and Southern Bay Foreshore catchments.

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Land use map for the Georges Bay Catchment