Module 4 - human impacts

Question 1

What is salinity and salinisation?

Answer 1

-Salinity is the concentrations of salts in water or soils.
-Salinisation is the process by which water-soluble salts accumulate in the soil.

Question 2

What is the water table

Answer 2

The water table is an underground boundary between the soil surface and the area where groundwater saturates spaces between sediments and cracks in rock

Question 3

what is dryland salinity

Answer 3

-Salinity degrades land by an increase in soil salt concentration in the environment, watercourse or soil in unirrigated landscapes, being in excess of normal soil salt concentrations in dryland regions.
-In semi-arid regions of the country, the water table underground is kept in balance by native trees and vegetation.
- The deep-rooted perennial (year round) trees absorb most water that enters soil and returns to the atmosphere via evapotranspiration (from leaves and soil)
Therefore the water added to soils by rainfall, called recharge, is roughly the same as the water used by the
deep-rooted trees. This is called the water table discharge.
- This keeps a stable balance between new water, such as through rainfall, and removal of water; the sub-terrestrial (water table) water levels are kept well below the surface.

Question 4

what is land clearing salinisation

Answer 4

Land clearing to make room for shallow rooted crops which only grew part of the year
- Absorbed only a fraction of rainfall compared to that of native deep-rooted vegetation.
- Reducing transpiration and increasing runoff and infiltration
- This raises the volume of the water table which brings dissolved connate salts with it.

Question 5

What is irrigation

Answer 5

-Irrigation is the artificial process of applying controlled amounts of water to land to assist in the production of crops
-Irrigation (artificial addition of water to land or soil)
- Inefficient use of this irrigation(e.g. excessive) contributes to salinity
- Because irrigated land is typically also land cleared (crops for agriculture), this leads to an even greater volume of water
infiltration causing a rise in the water table (containing dissolved connate salts).