Land-based activities, estuaries, coastal zone and marine environment are all intrinsically linked to each other. Figure1 develops a conceptual framework of the biophysical relationships relevant to oceans management and depicts the general geographical and institutional settings. Arrows represent impact relationships and indicate their directions. It should be borne in mind that Figure1, in the interests of clarity, simplifies a highly complex system and abstracts the relationships. Complex biological systems such as oceans may not show immediate and linear responses to use and management activities but are characterised by threshold behaviour as well as time lags and spatial distance between cause and effect.
Many impacts are indirect and some are cumulative.
Heavy metals are released in industrial production processes and bacteria and other biological carriers come from human and animal waste. The population increase along Australia's shorelines and corresponding industrial development have seen a rapid increase of sewage outflow into rivers, estuaries and oceans. In recent times, several incidents of people falling sick after the consumption of contaminated oysters have shown the direct impact of sewage and waste treatment and outflow on aquaculture and food safety. This reality is in conflict with the principles of waste minimisation and environmental protection. Land use and storm water systems influence the nutrient load of rivers as well as turbidity and sedimentation.