Water

Types and causes of urban stormwater pollution


Stormwater pollutants originate from many different sources, ranging from fuel and oil from our roads, to litter dropped on our streets and sediment from building sites. There are three main types of stormwater pollution:

  • litter — for example, cigarette butts, cans, food wrappers, plastic bags or paper
  • ‘natural’ pollution — for example, leaves, garden clippings or animal faeces
  • chemical pollution — for example, fertilisers, oil or detergents.

Common pollutants found in urban stormwater, their likely sources and the effect of the pollutant on our waterways

Pollutant Effect Urban source

Sediment

Reduces the amount of light in the water available for plant growth, decreasing the supply of food for other organisms.

Can clog and damage sensitive tissues such as the gills of fish.

Can suffocate organisms that live on or in the bed of lakes and streams by forming thick deposits when the suspended material settles out.

  • Land surface erosion
  • Pavement and vehicle wear
  • Building and construction sites
  • Spillage, illegal discharge
  • Organic matter (for example, leaf litter, grass)
  • Car washing
  • Weathering of buildings/structures
  • Atmospheric deposition

Nutrients

An increase of nutrients in water stimulates growth of aquatic plants. This causes excessive growth of aquatic weeds and algae that may choke lakes and streams and lead to dramatic daily fluctuations in dissolved oxygen levels.

  • Organic matter
  • Fertiliser
  • Sewer overflows, septic tank leaks
  • Animal faeces
  • Detergents (car washing)
  • Atmospheric deposition
  • Spillage, illegal discharge

Oxygen-demanding substances

Oxygen is used up more quickly than it can diffuse into the water from the atmosphere. The resulting drop in oxygen levels may then kill fish and other aquatic organisms.

If all oxygen in the water is used up, can cause unpleasant odours.

  • Organic matter decay
  • Atmospheric deposition
  • Sewer overflows, septic tank leaks
  • Animal faeces
  • Spillage, illegal discharges

pH (acidity)

Increased acidity damages plants and animals

  • Atmospheric deposition
  • Spillage, illegal discharge
  • Organic matter decay
  • Erosion of roofing material

Micro-organisms

Contain very high numbers of bacteria and viruses. Some of these organisms can cause illnesses, including hepatitis and gastroenteritis.

  • Animal faeces
  • Sewer overflows, septic tank leaks
  • Organic matter decay

Toxic organics

Can poison living organisms or damage their life processes.

  • Pesticides
  • Herbicides
  • Spillage, illegal discharge
  • Sewer overflows, septic tank leaks

Heavy metals

Poison living organisms or damage their life processes in some other way.

Persist in the environment for a long time.

  • Atmospheric deposition
  • Vehicle wear
  • Sewer overflows, septic tank leaks
  • Weathering of buildings, structures
  • Spillage, illegal discharges

Gross pollutants (litter and debris)

Unsightly.

Animals can eat and choke on this material.

  • Pedestrians and vehicles
  • Waste collection systems
  • Leaf-fall from trees
  • Lawn clippings
  • Spills and accidents

Oils, detergents and shampoos (surfactants)

Highly toxic to fish and other aquatic life.

  • Asphalt pavements
  • Spillage, illegal discharges
  • Leaks from vehicles
  • Car washing
  • Organic matter

Increased water temperature

High temperatures are lethal to fish and other aquatic organisms.

Increased water temperatures stimulate the growth of nuisance plants and algae.

This and other effects can lead to decreased levels of dissolved oxygen, which can threaten other aquatic life.

  • Run-off from impervious surfaces
  • Removal of riparian vegetation

 

Table modified from Table 1.1 in Urban stormwater best practice environmental management guidelines (published by CSIRO). 

Page last updated on 6 Jul 2012