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Water Quality

The role of ecosystems in the purification of water (e.g. pollution control, detoxification and waste assimilation).


Millennium Ecosystem Assessment Service Category

Regulating Services


What is water quality and how is it derived?

Good groundcover across the whole catchment is key to good water quality.

Rocky substrates enhance 'stream roughness' providing surface resistance minimising erosion by slowing water down.

Exposed ground upstream contributes to poor water quality downstream.

This service describes the output of filtration, the decomposition of organic wastes and pollutants in water, and the assimilation and detoxification of compounds through soil and subsoil processes. In recent years, the terms ‘waterway or river health’ and ‘water quality’ have almost become synonymous. The terms have been used in an increasingly broad way to cover many of the beneficial environmental and aesthetic ‘values’, ‘attributes’ or ‘qualities’ of water. As such, the description of water quality as a service provided by the environment to human beings, is most often linked to the ecological, societal and aesthetic values that we attach to water.

Table 1 below presents the magnitude different ecosystem functions (relative to other ecosystem functions) contribute to the purification of water that provides good water quality. Good water quality is provided mainly by the functions of our ecosystems to regulate water and nutrients, treat and assimilate wastes and facilitate biological control. Land cover, riparian vegetation, topography, soil types and hydrological conditions affect the spatial and temporal distribution of water on the land, aquifers, waterways and atmosphere which affects the transportation, storage and recycling of excess organic and inorganic wastes through distribution, assimilation and chemical recomposition. For example, wetlands remove harmful pollutants from water by trapping metals and organic materials; soil microbes degrade organic waste, rendering it less harmful.

Soil, regolith and vegetation act as buffers to the effects of wind and water (e.g. erosion) through water retention and energy storage. Adequate vegetation cover, root biomass and soil biota minimises soil loss and runoff into our waterways. Stream vegetation and rocky substrates enhance 'stream roughness' which provides more surface resistance to 'slow the water down'. This minimises erosion and runoff of sediment and associated nutrients into our waterways. 

The provision of shade and shelter prevents nuisance plant and algal blooms in our streams. In small streams, particularly upland streams, healthy riparian vegetation shades most of the channel and limits the amount of growth by limiting the amount of light that reaches the stream, particularly when excess nutrients are available. Excessive plant growth can result in a major decline in water quality as algae and large aquatic plants smother natural habitats, choke stream channels and increase the likelihood of floods. In addition, the growth and subsequent decay of these plants can severely deplete the water column of oxygen.

Water quality is further enhanced by the interactions within biotic communities that act as restraining forces to control population of potential pests and disease vectors. From a climate regulation perspective, land cover and biologically mediated processes regulate atmospheric processes and weather patterns which in turn create the microclimate required for different plants and animals that affect water quality to function effectively. While other functions including gas regulation, soil formation, supporting habitats, provision of raw materials, food and pharmaceutical production, pollination and provision of genetic resources may not have a significant implication in the provision of good water quality, these functions may indirectly affect the provision of this service.


Table 1:The relative magnitude (to other ecosystem functions) each ecosystem function contributes to Water Quality.

Ecosystem Function Category Ecosystem Function 0
Regulating Functions
Gas Regulation

Climate Regulation

Disturbance Regulation

Water Regulation

Soil Retention

Nutrient Regulation

Waste Treatment and Assimilation


Biological Control

Barrier Effect of Vegetation

Supporting Functions
Supporting Habitats

Soil Formation

Provisioning Functions

Raw Materials

Water Supply

Genetic Resources

Provision of Shade and Shelter

Pharmacological Resources

Cultural Functions
Landscape Opportunity



Dams and water treatment plants rely on the maintenance of ecosystem functions to reduce costs.

Overland and underground flows of water travel across our catchments into receiving ecosystems (e.g. rivers, coastal and marine ecosystems) or water storage areas (e.g. soils, lakes, dams and wetlands). Advanced membrane technology and new treatment processes means water of poor quality entering dams, the main storage areas for water for human consumptive purposes, can now be treated to be fit for different uses (e.g. drinking, agriculture, industrial applications). However the cost and energy requirements must be balanced against the tried and proven benefits of avoiding degradation of source water in the first instance (e.g. by maintaining ecosystem function). 

Major infrastructure in the form of dams and water treatment plants all rely on the ongoing maintenance of ecosystem functions. From a potable water supply perspective these functions are of vital importance as they are closely related to treatment effort, cost and risk to final consumers. The diminshment of these ecosystem functions would greatly increase the final cost of water quality. An excellent example of how improved catchment management (e.g. by restoring or improving ecosystem function) can reduce the costs and risks associated with water treament is the Catskills Project in New York.


Are there any barriers to people receiving this ecosystem service and its benefits?

Due to the relatively affluent nature of the SEQ region, residents and visitors are lucky enough not to experience many of the issues experienced by other regions across Australia or in other countries (e.g. unsanitary drinking supplies). Water for consumptive purposes is treated through massive industrial treatment plants that is paid for by consumers and subsidised by governments. The greatest barrier to people receiving this service in SEQ is cultural attitudes and practices. There is a dissassociation by many people of the role landscapes plan in the treatment of water and the cost of water as it comes from the tap. Natural disasters and extreme events can also impact on this ecosystem service.

This ecosystem service provides many benefits that contribute both directly and indirectly to the well-being of the SEQ community. The Constituents of Well-being this ecosystem service contributes to are presented in Table 2 below. Further information on these constituents and how ecosystem services contribute to them can be obtained by clicking on the links in the table. 

Table 2:The relative magnitude (to other ecosystem services) Food contributes to each constituent of well-being.

Well-being Category Constituent of Well-being 0
Physical Health            
Mental Health            
Secure and Continuous Supply of Services            
Security of Person            
Security of Health            
Secure Access to Services            
Security of Property            
Good Social Relations
Family Cohesion            
Community and Social Cohesion            
Freedom of Choice and Action
Social and Economic Freedom            
Self Actualisation            




Riparian vegetation filters nutrients and retains streambanks.

Community programs are integral to water quality monitoring.

Links to other publications and websites

Healthy Waterways
SEQ Catchments Water Monitoring
SEQ Water - Water Quality Policy
National Water Quality Monitoring

Extensive effort across the region goes into monitoring the quality of water in rivers and dams in SEQ. SEQ Water conducts routine and event monitoring programs, the Healthy Waterways Partnership provides a regional report card and numerous other government departments, local councils and community groups also monitor the health of the resource. Investigations into the health of the lower Brisbane River and Moreton Bay have shown that sediments and nutrients are the main pollutants and drivers of water quality of our waterways. Other studies have shown that the majority of these pollutants enter the waterways during the large storm events which are a regular feature of the sub-tropical climate in SEQ. As such, it is clear that the key to improving waterway health is to minimise runoff during these events by establishing healthy riparian vegetation along the banks of creeks and gullies.

As such, in SEQ, healthy riparian vegetation is the single, most important factor affecting water quality and the health of small streams. It is critical because it: a) stabilises banks and reduces channel erosion; b) reduces sediment running into Moreton Bay; c) slows water flow to small tributaries and reduces erosive power; d) it traps sediment, nutrients and other contaminants; e) shades streams so that in-stream productivity (i.e. plant growth) is maintained at natural rates; f) moderates stream temperature and keeps oxygen levels high; g) provides food and habitat for aquatic animals in the form of leaf litter, logs and branches; and h) provides terrestrial habitat for the adult stages of aquatic insects and semi-aquatic organisms such as frogs and turtles. Based on this, the provision of good water quality and healthy waterways can be monitored by measuring the condition of riparian buffers and the health of waterways. The indicators used by the SEQ Ecosystem Health Monitoring Program can assess if this service is provided effectively.


How is this ecosystem service currently managed in SEQ?

The Department of Environment and Heritage Protection administers the Environmental Protection (Water) Policy 2009 which seeks to achieve the objective identified by the Environmental Protection Act 1994 — to protect Queensland's waters by an integrated management program while allowing for development that is ecologically sustainable. The department monitors ecosystem health in rivers, estuaries and coastal areas throughout the eastern coast of Queensland. In addition, the department regulates industries through licensing waste outputs into waterways.

The Department of Energy and Water Supply oversees bulk water supply, distribution and retail arrangements in SEQ. The department administers the Water Supply (Safety and Reliability) Act 2008, its provisions regulate drinking water quality to protect public health. Registered water providers are required to develop a drinking water quality management plan the purpose of which is to implement a risk-management approach to manage the quality of drinking water. In a plan, the provider:

- gives details of the infrastructure of the registered service
- assesses the hazards and hazardous events that may affect drinking water quality
- undertakes a risk assessment and documents the process for managing these risks
- outlines day-to-day operational requirements for managing the system, including how mandatory criteria will be monitored, how operational and verification monitoring will be conducted and reporting arrangements to ensure safe water.