Adelaide Coastal Waters Study

More than 60 scientists from research organisations across Australia have brought their expertise to a $3 million, six year research program investigating the mysterious decline of Adelaide’s coastal seagrasses. The CSIRO-managed Adelaide Coastal Waters Study pieced together the complex story behind the loss of more than 5000 hectares of shallow sub-tidal seagrass in the Gulf St Vincent, adjacent to Adelaide’s shoreline.

The study was initiated by the South Australian Environmental Protection Agency to address growing concern about the effects of coastal and catchment development on the marine environment near Adelaide, particularly on coastal seagrasses. These concerns were justified, as results found that many years of near-continuous inputs of nutrient-rich, turbid, and coloured water and wastewater have resulted in significant changes to and degradation of this unique environment.

“Encouragingly, the water quality improvement plans which have been in place over the past 10 years, coupled with reduced volumes of storm and wastewater discharged to the sea have made a positive difference. However, it may take between 20 and 100 years for seagrasses to regrow and large scale recovery of seagrass meadows requires continued, lasting reductions in coastal inputs and a replanting effort,” says study director, Professor David Fox.

These photos, taken in November 2005 following a heavy spring rain event, show the aesthetic impacts of stormwater discharges with high levels of Coloured Dissolved Organic Matter (CDOM). Photo: © Simon Bryars, SARDI Aquatic Sciences

Adelaide’s coastal marine environment is unique because of the interactions between seagrasses, beach and near-shore morphology, seafloor organisms, nutrients and toxicants, and water quality. Yet understanding of these interactions and processes was inadequate to answer the question of why seagrasses were disappearing and, more importantly, what could be done to halt and reverse the problem.

The aim of the Adelaide Coastal Waters Study was to address knowledge gaps and develop an integrated understanding of the coastal ecosystem thereby providing the basis for more informed decision-making. It will assist in the development of a comprehensive management strategy, focussed on ecological priorities which take into account practical, economic, and social objectives. This strategy also underpins the research objectives of the Water for a Healthy Country Flagship program.

To ensure that an integrated view was achieved the research program was designed in consultation with key stakeholders, with research activities undertaken by a collaborative team of local and interstate research providers including CSIRO, Flinders University, South Australian Research and Development Institute (SARDI) Aquatic Sciences, Adelaide University, University of Western Australia and several private consultants.

“The study focussed on the loss of seagrasses (mainly Amphibolis and Posidonia seagrass), seabed instability, and water quality degradation,” says Professor Fox. “Seagrass meadows are primary producers at the bottom of the food chain and they provide natural habitat for many species of fish, crustaceans, and other marine animals. Taking the seagrasses out of the system causes a ‘domino effect’, where the seafloor becomes less stable and hence promotes a further loss of seagrass”.

The main issues investigated by the study included:

• the fate and impact of nutrients (nitrogen and phosphorus), and other contaminants implicated in seagrass loss,
• stormwater and wastewater inputs,
• seagrass ecology to identify what causes seagrass decline, the prospect of seagrass regrowth and the implications of seagrass recovery,
• how physical processes (such as wind, tides, currents and temperature) operate on a local and gulf-wide scale, and
• sediment sources and the role of sediment in seagrass loss.

The Adelaide Coastal Waters Study Final Report outlines 14 recommendations which aim to guide future management actions to enable this regrowth and recovery. These recommendations include:

• reduce the volumes of wastewater, stormwater and industrial inputs into Adelaide’s coastal environment
• reduce the amount of nitrogen discharged into the marine environment to 600 tonnes, which is a 75 per cent reduction from the 2003 value of 2400 tonnes
• a 50% reduction from 2003 levels of particulate matter loads discharged to the marine environment
• improve the optical qualities of coastal waters by reducing the amount of coloured, dissolved organic matter discharged by rivers, creeks and stormwater drains
• loads from sources such as the Port River, wastewater treatment plants and drains should continue to be reduced and toxicant loads and concentrations should be routinely monitored every 3 to 5 years
• implement an environmental monitoring program to detect changes in the coastal marine environment
• develop a single database of information and establish a research/monitoring coordination body to prioritise future research
• implement monitoring and mapping programs to assess seagrass health
• conduct further research to determine the extent of the influence of nitrogen from wastewater treatment plants and industrial outfalls and other potential sources
• complete an audit of key environmental assets, risks to those assets and develop a plan to mitigate the risks

To read more about the Adelaide Coastal Waters Study or download the Final Report please go to http://www.csiro.au/solutions/AdelaideCoastalWaters.html

Contact:
Professor David Fox, University of Melbourne
Email: david.fox@unimelb.edu.au