System Disturbances

To improve the resilience of a system, potential perturbations must be identified along with their foreseen effects. Managers will not be able to identify all the disturbances that a system can undergo or the effects that could result. Surprise events are inevitable and could be beyond the scale of influence of managers.

Tables 2, 3 and 4 show some of the environmental, social and economic disturbances that can and do affect the Port Phillip Bay system. The kind and duration of the shock is listed as to give an idea of how the system may be affected.

Below: Table 2: Environmental disturbances, type, frequency and possible effects







Annual/Decadal, Can Last a Single or Several Years

Reduced Runoff results in Bay and River Nutrient Input Reduction

Tourism and Water Based Recreational Activities Suffer

Social Impacts – Personal Water Restrictions and Creates Unrest

Potential Loss of Tax Revenue as Business and Industry Suffer

Need for Greater Government Spending to Deal With Crisis

Forest Fire Potential Increase Coupled With Wildfire Disease

Water Quality Effects, No Water Cycling and Freshwater Input

Potential Media, Social, Political, Environmental and Economic Conflicts

Increased Water Production and Transport Costs

Increased Rainfall in Wet Years



Increased Agricultural Production and Runoff Leading to Increased Nutrient Inputs

Water Dominated Businesses, Industry and Recreation Flourishes

Increased Potential for Flash flooding



Rare but sustained

Reduction in Secchi Depth and Photosynthetic Activity at Lower Depths

Oxygen profile changes

Algal bloom stimulation leading to eutrophication

Destruction of Sea grass and kelp bed habitats

Toxicant release effects pH balance and enters the food chain

Reduction in water body aesthetics effects tourism and land values

Sight reliant food locating species effected

Temperature Increases


Gradual Increase

Thermal expansion of water creates erosional problems on coasts

Bay temperature profile changes effects metabolic rates and decreases pH

Increasing demand for water and Health Impacts

Increased drought potential and evaporation rates

Sea Level Rise


Gradual but small increase

Threatens current beaches and thus tourist and recreational activity

Increased cliff failure and erosional events

Flooding potential increased

Loss of property value

Spills and Dumping



Poisoning of food chain

Increased eutrophication and loss of aesthetic value

Health impacts from physical contact and marine food consumption

Below: Table 3: Social disturbances, type, frequency and possible effects





Population Dynamics


Very Slow but Constant

Increased demand for goods and services when population growing

Pressures on environment such as agriculture and water supplies

Increasing use of and demand for local businesses and government services

Increased urbanisation and fertiliser use

Increasing Traffic creates pollution and health problems

Terrorist Event or Global Pandemic


Unpredictable and Effects could be sustained

Keeps tourists and capital investment away from areas

Can affect local attitudes

Local health of population could be effected

Potential infrastructure and business market destruction

Institutional Changes

Pulse and Press

Greatly depends of type of change

Policy and jurisdictional changes can result in management practise changes

Potential social, economic and environmental changes

Budget changes can have positive or negative effect

Could potentially have effects at all scales

Below: Table 4: Economic disturbances, type, frequency and possible effects





Financial Instability

Pulse and Press

Unpredictable, can last years or even decades

Reduced demand for goods and services

Reduced demand for shipping and imported goods

Reduction in disposable income effects recreation and tourism

Higher energy and production costs

Exchange rates and land values effected

Government revenue reduced impacts on departmental budgets

Exchange Rate Dynamics


Constantly Fluctuating

Currency devaluation promotes tourism and exports

Currency appreciation promotes imports and puts tourists off

Effects demands for goods and thus shipping and transport

Environmental Budget Cuts


Depends on Government changes and  priority shifts

Effects management practises

Can produced ineffective environmental assessments

Research and development affected

Could amplify any current impacts if interventions are scaled back

Some disturbances are known to reoccur. El Nino, exchange rate fluctuations and institutional based changes will occur time after time. The issues lie in that the details cannot be predicted as easily. The timing of an El Nino event cannot be predicted (Chen et al., 2004) and the amount the Australian dollar will fluctuate on any given day is unknown. What I critical is the idea that surprise events will occur that result in surprise effects. The following tables highlight some of the disturbances that could affect Port Phillip Bay.

The disturbances listed here are not exhaustive and a merely a guide for managers on the range and types that Port Phillip Bay could be subjected to.

Previous: Historic Indicators

Next: Stable States and Thresholds


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