What is Salinity: Types, Causes and Measure | Civil Engineering Optional Notes for UPSC PDF Download

What is Salinity?

Salinity measures the concentration of dissolved salts in soil or water, typically expressed in parts per million (ppm) or as a percentage of the solution's total weight. In water, salinity is determined by measuring the electrical conductivity (EC) of the solution; higher conductivity indicates higher salinity. High salinity levels can negatively affect crop growth and drinking water quality.

• Scientifically, salinity influences water density, temperature, and other physical properties. For example, water with higher salinity is denser, impacting ocean currents and water movement in lakes and rivers. It also affects the freezing and boiling points of water, which can influence weather patterns and freshwater availability.
• Biologically, salinity impacts which organisms can survive in a given body of water. Some organisms, such as certain fish and algae, thrive in high salinity environments, while others, like freshwater fish and plants, require lower salinity levels. Changes in salinity can lead to the displacement or extinction of species, with broader ecological implications.

Water and Soil Salinity

Soil Salinity

Types of Salinity

There are two types of salinity: primary and secondary.

• Primary salinity: Occurs naturally in soil or water, commonly found in arid and semi-arid regions where high temperatures and low rainfall cause salt accumulation.
• Secondary salinity: Results from human activities like irrigation, mining, and industrial processes adding salts to soil or water.

How to Measure Salinity?

Measuring salinity is essential for determining the suitability of water or soil for agricultural purposes. Common methods include:

• Electrical conductivity (EC) measurement: Uses a handheld EC meter to measure the solution's conductivity, which correlates with salinity.
• Total dissolved solids (TDS) measurement: Measures the total amount of dissolved ions in a sample, expressed in ppm or mg/L, using a TDS meter.
• Chloride ion concentration measurement: Uses a chloride ion-selective electrode to measure chloride ions, common in saline soils and water.
• Sodium adsorption ratio (SAR) measurement: Calculates the suitability of water for irrigation based on sodium, calcium, and magnesium ion concentrations.
• Soil sampling and laboratory analysis: Involves collecting soil samples and sending them to a lab for salinity analysis, often using the saturated paste extract method.

Causes of Salinity

Salinity arises from natural and human factors.

Causes of Soil Salinity

• Irrigation: Evaporation of irrigation water leaves salts behind, leading to soil salinization, especially in arid regions.
• Poor Drainage: Accumulated water dissolves and transports salts deeper into the soil, causing salinization over time.
• Natural Causes: Weathering of rocks, volcanic eruptions, and salt deposits can cause localized soil salinity.

Causes of Water Salinity

• Natural Causes: Weathering of rocks, evaporation, and seawater intrusion can increase water salinity.
• Human Activities: Agriculture, mining, and urbanization contribute to water salinity through irrigation, fertilizer use, wastewater discharge, and stormwater runoff.

Prevention and Mitigation of Soil and Water Salinity

Addressing salinity requires a combination of natural and human interventions:

• Improving Irrigation Practices: Techniques like drip irrigation can reduce evaporation and leaching.
• Enhancing Drainage: Installing drainage pipes or constructing canals can help excess water drain away from soil.
• Planting Salt-Tolerant Crops: Using crops that tolerate high salinity can reduce irrigation and fertilizer needs.
• Reducing Water Pollution: Implementing best management practices in agriculture and mining, and reducing industrial wastewater discharge can prevent water salinity.

Conclusion

Soil and water salinity are complex issues requiring multifaceted prevention and mitigation approaches. Understanding salinity causes helps develop effective strategies, such as improving irrigation practices, enhancing drainage, planting salt-tolerant crops, and reducing water pollution. These interventions can mitigate the environmental and health impacts of salinity.