Salinity problems in some dryland areas are primarily caused by the removal of native vegetation and its replacement with agricultural crops and farming practices.
This fundamental land use change significantly disrupts the natural water balance of the environment, leading to conditions where salts present in the soil and groundwater are brought closer to the surface.
Understanding the Cause
The core reason for dryland salinity, as highlighted by research, is the alteration of the natural hydrological cycle.
The Role of Native Vegetation
- Native plants, especially trees and deep-rooted perennials, are highly effective at using available rainwater.
- Their extensive root systems absorb water from deeper soil profiles.
- This efficient water usage helps keep the groundwater table at a lower level.
How Agriculture Changes the Balance
- When native vegetation is cleared and replaced with annual crops or pastures, less water is used by the plants.
- Agricultural crops often have shallower root systems and are not present year-round, leading to less water uptake overall.
- Excess water then infiltrates deeper into the soil, recharging the groundwater table.
The Impact on Groundwater
The provided reference specifically states: "The removal of native vegetation and its replacement with agricultural crops and farming practices has resulted in significant change to the water balance in many areas."
This change means more water reaches the groundwater. When the groundwater table rises, it brings dissolved salts upwards towards the root zone and the surface.
- Rising Groundwater: The increased recharge from agricultural land pushes the water table higher.
- Salt Accumulation: As the water evaporates from the surface, the salts are left behind, accumulating in the topsoil and root zone.
- Salinisation: This process, where salt concentrations increase, is known as salinisation.
The reference further notes: "If groundwater levels remain static, or rising, then salinisation will persist and may expand." This emphasizes the direct link between elevated groundwater levels resulting from land use change and ongoing salinity issues.
Consequences of Salinity
Increased salinity in dryland areas has several detrimental effects:
- Reduced Crop Yields: Most agricultural crops are sensitive to high salt levels in the soil, leading to stunted growth and reduced productivity.
- Loss of Arable Land: Severe salinisation can render land unsuitable for farming.
- Damage to Infrastructure: Salts can damage roads, buildings, and pipes.
- Environmental Degradation: Native vegetation, streams, and wetlands can be harmed by increased salt concentrations.
In summary, the shift from deep-rooted native vegetation to agricultural systems alters the water balance, causing groundwater tables to rise and mobilizing salts, ultimately leading to dryland salinity problems.
