River Murray and Lower Lakes catchment risk assessment for water quality: Results and management options 7 Goolwa to Wellington and Coorong District LAP areas assessment 7.1 Description of the area This chapter combines the two Local Action Planning (LAP) areas: Goolwa to Wellington (GW) and the Coorong District (CD). The key water resources within this region are the large (85,000 ha) and shallow (2–3 m deep) freshwater Lakes Alexandrina and Albert, and the saline Coorong (140 km long, 2–3 km wide)( Figure 7.1). The River Murray enters Lake Alexandrina near Wellington and Lake Albert is connected to Lake Alexandrina by a narrow passage near Narrung. The Lower Lakes and Coorong are highly ecologically significant (see eg Phillips et al. 2005) and have been identified as one of six significant ecological assets across the entire Murray–Darling Basin. The region was selected because of its unique ecological qualities and hydrological significance and social, cultural and economic values for local and state communities including the Ngarrindjeri, the traditional owners of the region, for whom the lands and waters (or Ruwe), are a living body (MDBC 2005). Goolwa to Wellington LAP The GW LAP area, in the southernmost section of the Murray–Darling Basin, covers an area of about 265,000 ha11 and includes the townships Goolwa, Clayton and Milang (Alexandrina Council jurisdiction). The Goolwa population of about 2400 swells during holiday periods and residential development is currently increasing in the area. The LAP area includes a large area of Lake Alexandrina and encompasses all the plains and catchments that drain into the lake, from Goolwa to Wellington. This includes Currency Creek, Tookayerta, Finniss, Angus and Bremer-Barker catchments, and adjoining plains. Hindmarsh and Mundoo Islands at the mouth of the River Murray are also included. The main agricultural land use on the plains is cropping but there are also dairy farms, vineyards and vegetable production. Grazing is the main land use on Hindmarsh and Mundoo islands. Water management in the catchment area has undergone a number of significant changes in the last 150 years with diversion of surface drainage, construction of dams, groundwater extraction and establishment of an irrigation industry (CSIRO 2004). Land and water salinisation is currently a major problem, and salt and stream salinity levels are predicted to rise in the future (Dooley & Henschke 1999). Salinisation, wetland and watercourse degradation, lakeshore erosion, overuse of water resources and irrigation management are key issues being targeted by the GW LAP group12 and other agencies. Coorong District LAP The CD LAP area extends from just above Tailem Bend and Peake in the north, to just above Keith in the Upper South East (USE). Coorong National Park, Lake Albert and Lake Alexandrina form its western boundary (Figure 7.1). The land area covers 883,500 ha, the lakes 46,800 ha13. Townships include Meningie and Raukkan (Coorong District Council jurisdiction). Land use in this LAP area is predominantly a mixture of cropping and grazing with 0.6% of the area irrigated for dairies, fodder and lucerne seed (CD LAP 2000). Significant areas of wetlands and national parks lie within the CD LAP area, as does the mouth of the River Murray. 11,13 This report only considers the portion of the LAP area that is part of the water protection areas defined under the Environment Protection Act 1993 and River Murray Act 2003. 12 See website <www.rivermurray.sa.gov.au/lapgroups/goolwa> for more information 191 River Murray and Lower Lakes catchment risk assessment for water quality: Results and management options The highest priority issues identified in the local action plan for the area (CD LAP 2000) are dryland salinity control and remnant native vegetation, wetlands, and habitat protection and enhancement. An estimated 250,000 hectares or 40% of the land in the USE district part of the CD LAP (productive farmland, native vegetation and wetlands) have been degraded by salinisation caused by high groundwater levels and flooding. A further 200,000 ha including approximately 40,000 ha of high value wetlands are at risk. This is by far South Australia’s largest and most severe case of dryland salinity. The USE Dryland Salinity and Flood Management Program, with a total funding commitment of $49.3 million, is undertaking 410 km of drainage works, wetlands management and restoration, and improved management of remnant vegetation and wetland habitat. As at 30 September 2005, approximately 200 kilometres of open cut drains have been completed. Morella Basin is used to retain drainage water prior to periodic releases (4000–10,000 ML per annum) into Salt Creek and the Coorong. Flow and circulation in the Lower Lakes and Coorong Not only have water flows in the GW & CD LAP area catchments been modified extensively, in the last 100 years human intervention has also greatly modified the flow and water circulation in the Lower Lakes and Coorong. Historically, this estuarine environment had wide fluctuations in salinity and water levels (Walker 2002, Gell & Haynes 2005). Since the 1940s, several barrages have been constructed to maintain more freshwater conditions in the lakes and lower reaches of the river. The Murray mouth closed over in 1981 and was reopened by dredging, a condition that was maintained for some time by river flows. The subsequent decline in peak (spring) flow levels has seen the mouth has become greatly restricted in recent years (Walker 2002). Only regular dredging of the Murray Mouth now maintains a channel through the sand bars to the open ocean. The Coorong is also now a much more ‘closed system’ than in the past with the southern lagoon being hyper-saline for much more extended periods of time (DWLBC 2005) than in pre-European settlement times (Gell & Haynes 2005). Human interventions have reduced tidal flushing rates (through the Murray mouth, see above) and regular freshwater inputs from the South East region into the southern lagoon of the Coorong (Gell & Haynes 2005). Sedimentation rates have also markedly increased in the Coorong (Gell & Haynes 2005). It is clear that improved flow regimes are essential for improving water quality and ecosystem health in the Lower Lakes and Coorong. A Lower Lakes, Coorong and Murray Mouth Asset Environmental Management Plan (MDBC 2005) has been drafted which looks at how flows could be managed better in the area. As it is already addressed by these other initiatives, this current report does not specifically look at flow management. Water quality Various agencies and volunteer groups (eg DWLBC, DEH, EPA, Waterwatch) carry out a large amount of monitoring in the Lower Lakes and Coorong. DWLBC is preparing a summary of the monitoring in this area which will provide a valuable resource to ensure monitoring programs are coordinated, and promote collaborations and information sharing. 192 River Murray and Lower Lakes catchment risk assessment for water quality: Results and management options Figure 7.1 and Coorong District LAP areas Goolwa to Wellington 193 River Murray and Lower Lakes catchment risk assessment for water quality: Results and management options The water quality of Lakes Alexandrina and Albert has been noted in the past as being poor (EPA 1998a, b) as a result of: • high turbidity in Lake Alexandrina (influenced by wind action readily suspending sediment in the shallow water depth) • moderate nitrogen and phosphorus concentrations • concentrations of heavy metals exceeding national guidelines for the protection of aquatic ecosystems at some sites • salinity exceeding the guidelines for good quality drinking water at some sites • pollutant inputs from rivers (eg Angas, Bremer, Murray). Although detailed load information was not obtained, it was assumed that pollutant loads from the River Murray itself were the biggest influence on water quality in the Lower Lakes. The River Murray was not specifically assessed as a hazard in this chapter; its risks have been assessed separately in previous chapters of this report. Other creeks and rivers were assessed as point source hazards as a detailed catchment risk assessment was outside the scope of this stage of the study. The first recorded incidence in Australia of animal poisoning from a blue-green algal bloom was in Lake Alexandrina, in the late 1800s. Cattle, horses, pigs, sheep and dogs died after drinking water covered by a scum of the blue-green alga Nodularia spumigena. Algal blooms in the lake since then(Codd et al 1994) include a recent Nodularia sp outbreak. Salinity reduces the Coorong’s water quality: reduced tidal flushing and freshwater inputs (Gell & Haynes 2005) lead to prolonged hyper-saline conditions in the southern lagoon (DWLBC 2005) where salinity levels are often elevated above the tolerance of many aquatic species. The southern lagoon is now almost devoid of macrofauna (Dittman et al 2006). The USE Dryland Salinity and Flood Management Program releases are having a freshening effect on salinity of the Coorong near the mouth of Salt Creek (DWLBC 2005). 7.2 Environmental value zones Spatial zones assigned for each environmental value allowed hazards to be identified and assessed for risk in manageable amounts. Aquatic ecosystem zones Risks to aquatic ecosystem health were assessed for the entire Lower Lakes and Coorong area. Raw water supply zones There are no large public raw water supply off-takes in the Lower Lakes and Coorong area so risks to this environmental value were not assessed in