Human impact on nature Plan: Human impact on nature

Irrigation[edit]
Main article: Environmental impact of irrigation
The environmental impact of irrigation includes the changes in quantity and quality of soil and water as a result of irrigation and the ensuing effects on natural and social conditions at the tail-end and downstream of the irrigation scheme.
The impacts stem from the changed hydrological conditions owing to the installation and operation of the scheme.
An irrigation scheme often draws water from the river and distributes it over the irrigated area. As a hydrological result it is found that:

• 
  the downstream river discharge is reduced
  
• 
  the evaporation in the scheme is increased
  
• 
  the groundwater recharge in the scheme is increased
  
• 
  the level of the water table rises
  
• 
  the drainage flow is increased.
  

These may be called direct effects.
Effects on soil and water quality are indirect and complex, and subsequent impacts on natural, ecological and socio-economic conditions are intricate. In some, but not all instances, water logging and soil salinization can result. However, irrigation can also be used, together with soil drainage, to overcome soil salinization by leaching excess salts from the vicinity of the root zone.^[61][62]
Irrigation can also be done extracting groundwater by (tube)wells. As a hydrological result it is found that the level of the water descends. The effects may be water mining, land/soil subsidence, and, along the coast, saltwater intrusion.
Irrigation projects can have large benefits, but the negative side effects are often overlooked.^[63][64]
Agricultural irrigation technologies such as high powered water pumps, dams, and pipelines are responsible for the large-scale depletion of fresh water resources such as aquifers, lakes, and rivers. As a result of this massive diversion of freshwater, lakes, rivers, and creeks are running dry, severely altering or stressing surrounding ecosystems, and contributing to the extinction of many aquatic species.^[65]