Diffuse source water pollution is less commonly recognised than point source water pollution because it arises in a catchment from many different sources that do not have an obvious discharge point. Diffuse pollution is caused when pollutants from a range of dispersed urban and rural land use activities contaminate our waterways and groundwater as a result of rainfall, soil infiltration and surface runoff. The source of this pollution is the widespread input of diverse types of contaminants.
Typical examples of diffuse pollutants include:
- nutrients, e.g. from overuse of fertilisers in agriculture and forestry
- sediments, e.g. from soil erosion
- pathogens, e.g. bacteria from leaking septic tanks
- toxicants, e.g. pesticides from a wide range of land uses
- salts, e.g. from dryland salinity
- acids, e.g. from acid sulfate soils in drained wetlands
- contaminants from roads and paved areas
- atmospheric deposition, e.g. contaminants arising from industry
-
gross pollutants, e.g. litter.
Diffuse distribution of chemical substances is ubiquitously occurring including urban spaces as well as rural regions. Industrial development has brought prosperity to millions of people but has also left a legacy of environmental damage that continues to impact natural resources and ultimately the human wellbeing. A wide range of man-made chemicals designed for use in industry, agriculture, pest control, consumer goods and emissions from the combustion of fossil fuels are the main sources for diffuse pollution of soils.
Within the water cycle, soils act as the key zone for storage, filtration and transport of water and associated pollutants. If the accumulation of pollutants exceeds the buffer capacity, then soils or sediments can become a source of diffuse pollution releasing pollutants to adjacent compartments such as groundwater and surface waters.
Diffuse inputs to soil and groundwater can be of various nature. Typical inputs resulting in soil contamination are:
- Agricultural practices; i.e. direct input of nutrients (fertilisers) and pesticides, application of sewage sludge and manure.
- Atmospheric deposition of exhaust gases and particles from vehicles and industry.
- Sedimentation of diffuse particles from waste water discharges in surface waters
Major impacts of diffuse inputs to soil and groundwater are:
- Decrease of soil quality,
- Decrease of groundwater quality due to leaching processes of nutrients, organic matter, and pesticides and other pollutants
- Eutrophication of surface waters due to sedimentation processes.