This page describes some of the main pressures on the marine water quality in Western Port. They are barriers to achieving this strategy’s targets so planning and action will need to find ways to minimise their effects.
The condition assessment shows that Western Port’s water quality is generally good. However, the nature of Western Port’s physical environment makes the quality of its marine waters particularly vulnerable to adjacent agriculture, residential, industrial and port development.
The main sources of pollutants from catchments, are freshwater inflows, coastal erosion and coastal infrastructure. Climate change is a long-term and significant risk to Western Port’s marine waters.
Much of the information about pressures has been sourced from ‘Understanding the Western Port Environment: A summary of current knowledge and priorities for future research', published by Melbourne Water in 2011.
Some 50 million cubic metres of earth are estimated to have been transported to Western Port by eroding tributary streams between the 1920s and 1970s. Although incoming sediment loads have been significantly reduced, existing deposits are daily re-suspended by tides and wave action.
In addition to the sediments already deposited, an estimated 62,000 tonnes of fine sediments are still deposited in Western Port each year from its rural catchments. The main catchment sources of suspended sediments are the Lang Lang and Bunyip Rivers.
Turbidity from high marine sediment loads are believed to be the major cause of the loss of 70% of Western Port’s seagrass during 1970s and 80s. Sediment is also filling the deep tidal channels that are important to the bay’s habitat diversity.
Suspended sediments change the light and water conditions for algae, seagrasses and seafloor-dwelling organisms. When they settle from the water column they can smother photosynthetic surfaces of algae and clog the feeding structures of animals.
Western Port is generally considered to have low nutrient inputs relative to other Bays including Port Phillip Bay. There is no direct sewage discharge, and the catchment inputs are comparatively small. The most significant catchment-sourced nutrient inputs are from Watsons and Corinella Creeks.
Nearly 20km of Western Port's northern and north-eastern coastal clay banks suffer from severe erosion. This is believed to be contributing about 30% of the 62,000 tonnes of suspended sediments still entering Western Port each year.
Infrastructure development at many scales, from constructed rock walls to port development, affect marine water quality by interrupting natural coastal erosion and rebuilding, reducing animal and plant diversity, disturbing acid sulphate soils and introducing chemical and toxicant pollution risks.
The Port of Hastings development is one of Victoria’s major infrastructure projects and is expected to be staged over the next 10-15 years. The current port and future development site comprises 8 km of shoreline and approximately 3500Ha of adjacent land north of the Hastings town area. Environmental protection is a critical element of the development plan and the development is subject to assessments required by the Victorian and Australian Governments.
Climate change is expected to reduce long-term river flows but increase the frequency and intensity of floods. These could increase the volumes of pollutants and sediments in Western Port.
Coastal Ramsar wetlands and agricultural land on Western Port’s low-lying northern coast are vulnerable to sea-level rise. Global sea levels are projected to rise between 0.18 to 0.59 m by 2095, with a possible additional contribution from ice sheet melts of 0.1 to 0.2 m. Larger contributions to global sea level rise from more rapid melting of polar ice sheets are possible.
Marine environments will be affected by increased water temperatures and acidification. Warmer waters are already creating changes to the distribution of marine plants and animals. Acidification increases the energy marine crustaceans and planktons need to create their calcium carbonate shells. The loss of these animals could have catastrophic effects on marine food chains and ecological systems.
The marine water in Western Port has been assessed (Method & Condition). Lead organisations are committed to achieving the targets (targets) and arrangements are in place to monitor and report on progress and success.
Targets and leadership arrangements are determined in consultation with relevant departments, agencies and delegated land managers.