Land and Water Link

September 2002

Maintaining the Health of Adelaide's Coastal Waters

Heavy losses of seagrasses, murky water, erosion and pollution from stormwater, municipal wastewater and industrial discharges are among the warning signs for Adelaide's coastal waters, according to preliminary findings of the Adelaide Coastal Waters Study managed by CSIRO Land and Water. To maintain the city's coastal waters in healthy condition is likely to require careful management in future, says the Director of the Adelaide Coastal Waters Study, CSIRO Land and Water's Dr David Fox. The study, which covers an area from Port Gawler to Sellicks Beach and 20 kilometres out to sea, aims to fill large gaps in understanding of how the coastal environment functions, as a guide for its future sustainable management. Rising public and government concerns over signs of coastal degradation have emerged gradually during the past half-century. In particular, concern has focused on the impact on coastal waters of polluted nutrient-rich wastewater from municipal sewage treatment plants and stormwater off the city's streets, and the lack of urban water recycling. The effectiveness of recent investments in stormwater infrastructure is yet to be established. Pollution studies show moderate to high turbidity (murkiness) and contamination by PCBs, lead, zinc and copper, as well as high ammonia and chlorophyll concentrations. Elevated nutrient conditions are conducive to the formation of toxic algal blooms. 'We know that a total of 4000 hectares of seagrass has been lost from the area between Aldinga and Largs Bay in the past 50 years. This peaked in the late 1970s when up to half the seagrass beds off Glenelg and West Beach were destroyed. Partly as a result of this, there is now far more sediment in coastal waters, with up to 100,000 tonnes more sand being dumped on the beaches each year', Dr Fox explains. 'This process has also changed the sea floor profile in parts of the coastal zone, which in some cases magnifies coastal erosion. The seagrass losses also bring a dramatic 40-fold decline in the range of species that inhabit the area, when it changes to a bare sandy bottom.' 'Effluent discharges and increasing sediment threaten both the abundance and diversity of creatures living on coastal reefs. Cabbage weed is starting to smother mangrove seedlings in some areas, and in others, the exposure of a clayey bottom has increased the risk of alien marine pests moving in.' Dr Fox says that the Mediterranean fan worm, Sabella spallanzani, may have already colonised up to 3500 hectares in Gulf St Vincent, and there is a constant risk of invasion by exotic seagrasses. The Adelaide Coastal Waters Study is now moving to Stage 2, which will entail two-and-a-half years of close investigation into how the coastal environment functions and copes with the impact that human activities have on it. Its key tasks include:

• quantifying the amount and sources of pollution from the land entering Adelaide's coastal waters
• working out the effect this has on seagrasses and other marine life
• mapping and trying to understand historical changes in seagrass patterns
• working out where the sediment comes from, and where it ends up
• understanding the patterns of water circulation along the Adelaide and Gulf St Vincent coastline
• devising a long-term monitoring program to keep watch on the health of the city's coastal waters.

The overall objective of the study is to develop understanding and tools to enable sustainable management of Adelaide's coastal waters by identifying causes of ecosystem modifications and the actions required to halt and reverse degradation. The study will focus on seagrass loss, seabed instability and water quality degradation. The $4 million project involves scientists from various research institutions including CSIRO. The project is funded by SA Water, the SA Environment Protection Authority, Transport SA, the SA Coast Protection Board, three metropolitan Catchment Water Management Boards (Patawalonga, Torrrens and Onkaparinga), Mobil Adelaide Refinery and TXU Torrens Island, with additional support from the SA Conservation Council, the Local Government Association and the South Australian Fishing Industry Council. The study aims to provide options for management actions in Adelaide's Coastal Waters and a program for assessing their effectiveness including a monitoring program. Further information

Contact

Mr David Ellis
Project Coordinator
Ph: 08 8303 8420