The Hydrologic Cycle and Water Pollution: A Comprehensive Guide

Posted on May 5, 2024 in Geology

T4. The Hydrologic Cycle

Water on Earth exists in a constant volume, but it’s always moving and changing its physical state. This process, known as the hydrologic cycle, connects the hydrosphere with the atmosphere, geosphere, and biosphere.

Internal Cycle

Driven by heat and density differences within the Earth, this cycle involves “juvenile water” of magmatic origin. It emerges through volcanic eruptions, deep-sea vents, or mixes with existing water from the external cycle.

External Cycle

Powered by solar energy and gravity, this cycle involves evaporation, evapotranspiration, precipitation, runoff, and infiltration. It occurs both in the atmosphere and on the Earth’s surface.

Evaporation and evapotranspiration from water bodies and living organisms form clouds, which release water as precipitation (rain, snow, or hail). This water either becomes surface runoff, infiltrates the ground to form aquifers, or is cycled through living organisms.

Effects of the Hydrologic Cycle

The hydrologic cycle regulates the Earth’s surface temperature, transfers energy, causes erosion, transports sediments, and periodically discharges water over continents.

T.5: Water Use and Pollution

Water Consumers

These users consume water and either don’t return it to its source or degrade its quality. Examples include:

• Urban activities: Meeting the needs of municipalities and households.
• Agriculture and livestock: Consumes significant water, with efforts underway to improve efficiency through methods like drip irrigation.
• Industrial uses: Varied applications such as solvents, cleaning, and manufacturing processes.

Non-Consumptive Water Uses

These uses don’t remove water from the environment. Examples include:

• Recreational use: Fishing, boating, swimming, etc.
• Habitat for living organisms: Maintaining healthy ecosystems.
• Hydroelectric power generation: Utilizing water flow to produce energy.
• Transportation: Using waterways for transport, though this is limited due to environmental concerns.

Water Pollution

Water pollution occurs when its physical, chemical, or biological properties are altered, making it unsuitable for use. Sources of pollution include:

• Anthropogenic pollution: From agriculture, livestock, industry, and urban activities.
• Natural contamination: Caused by living organisms, volcanoes, or lightning.

Types of Contamination

• Physical contamination: Suspended particles that reduce light penetration and harm aquatic life.
• Chemical contamination: Organic and inorganic substances like nutrients, heavy metals, and radioactive elements.
• Biological contamination: Pathogens and microorganisms that can cause disease.

Water Quality Parameters

Several parameters determine water quality:

Physical Parameters

• Organoleptic characteristics: Smell, color, and taste provide immediate information about water quality.
• Temperature: Ideal for consumption between 8 and 15°C.
• Turbidity: Measures suspended solids, which can be settleable or non-settleable.
• Conductivity: Indicates the presence of ions in the water, with high levels suggesting hard water.

Chemical Parameters

• Biochemical Oxygen Demand (BOD): Measures the amount of oxygen consumed by microorganisms to decompose organic matter.
• Chemical Oxygen Demand (COD): Measures the total amount of oxidizable matter in the water.
• Total Organic Carbon (TOC): Measures the total amount of organic compounds present.
• Dissolved Oxygen (DO): Crucial for aquatic life and self-purification processes.

Water Treatment and Purification

Drinking Water Treatment

Typically involves three stages:

• Decantation: Removing suspended particles using sedimentation and flocculants.
• Filtration: Passing water through sand or other media to remove remaining impurities.
• Disinfection: Using chlorine, hypochlorite, ozone, or ultraviolet radiation to kill pathogens.

Wastewater Treatment

Wastewater treatment plants reduce pollution levels to facilitate natural purification, enable water reuse, and protect public health. Different treatment systems exist, including low-cost and conventional methods.

T.6: The Wilson Cycle

The Wilson Cycle describes the cyclical process of supercontinent formation and breakup. The stages include:

1. Continental Rift Formation: Mantle plumes cause the lithosphere to stretch and fracture, creating a rift valley.
2. Ocean Formation and Continental Separation: The rift widens, forming a narrow ocean that eventually becomes an Atlantic-type ocean.
3. Subduction: The older, denser oceanic lithosphere subducts beneath the lighter continental lithosphere, forming trenches and volcanic arcs.
4. Orogen Formation: Collision of oceanic and continental plates or two continental plates creates mountain ranges.
5. Continental Collision: The subduction process consumes the oceanic plate, leading to the collision of two continents and the formation of a supercontinent.

The Wilson Cycle is a continuous process, with the early stages being extensional and the later stages being compressional. It explains the formation and breakup of supercontinents like Pangea.