Understanding Water Pollution: Causes, Effects, and Solutions

Posted on Nov 15, 2024 in Geology

Water Pollution

Water pollution occurs when substances or energy forms are discharged into water bodies, altering their natural composition and quality. The severity of pollution depends on the intended use of the water. It’s primarily caused by human activities, directly or indirectly, and harms living organisms, human health, and ecosystems.

Types of Water Pollution

We can distinguish between two main types of water pollution:

  • Diffuse Pollution: Its origin is not clearly defined, affecting large areas without a specific source.
  • Point Source Pollution: Produced by a particular source and affecting a specific area.

Water Pollutants

Water pollutants include chemicals, living organisms, or energy forms present in higher-than-normal concentrations.

Eutrophication

Eutrophication is the increase in primary productivity caused by the introduction of nutrients, primarily phosphorus and nitrogen compounds, from agricultural and domestic sources. The process unfolds as follows:

  1. Nutrient Input: Increased levels of nitrogen (N) and phosphorus (P) enter the water body.
  2. Phytoplankton Growth: Excess nutrients fuel the rapid growth of phytoplankton (algae).
  3. Reduced Light and Photosynthesis: The dense algal blooms cloud the water, reducing light penetration and hindering photosynthesis in submerged plants.
  4. Oxygen Depletion: As the algae die and decompose, they consume large amounts of oxygen, leading to oxygen depletion (hypoxia) in the water.
  5. Death of Aquatic Life: Oxygen depletion can cause the death of fish and other aquatic organisms that rely on dissolved oxygen.
  6. Cyanobacteria Blooms: As nitrogen becomes depleted, phytoplankton die off, and cyanobacteria (blue-green algae) may proliferate, potentially producing toxins.
  7. Sediment Accumulation: Dead algae and other organic matter accumulate on the bottom, further increasing oxygen demand.
  8. Anaerobic Conditions: In severe cases, the bottom waters become anoxic (lacking oxygen), leading to the growth of anaerobic bacteria that produce foul-smelling gases like methane, hydrogen sulfide, and ammonia.

Aquifer Exploitation and Saline Intrusion

Over-extraction of groundwater from aquifers can lead to several problems:

  • Lowering Water Tables: Excessive pumping can significantly lower the water table, reducing the availability of groundwater resources.
  • Saline Intrusion: When groundwater extraction exceeds the recharge rate, seawater can intrude into coastal aquifers. This occurs because seawater is denser than freshwater and can fill the void left by depleted groundwater. Saline intrusion contaminates the aquifer, making the water unsuitable for domestic, agricultural, and ecological uses.

Air Pollution and Acid Rain

Issue and Susceptibility

  • Emission: The amount of pollutants released into the atmosphere by a source over a specific period.
  • Susceptibility: The concentration of pollutants in a given area after they have been transported, mixed, and dispersed, potentially affecting living organisms and materials.

Acid Rain

Acid rain refers to the deposition of acidic compounds, primarily sulfuric acid and nitric acid, from the atmosphere onto the Earth’s surface. It can occur as rain, snow, fog, or dew.

Acid rain formation begins with the release of sulfur dioxide (SO2) and nitrogen oxides (NOx) into the atmosphere through combustion processes. These gases undergo chemical reactions, forming sulfuric acid and nitric acid, which dissolve in atmospheric water droplets and can be transported long distances by wind before falling back to the ground as acid rain.

Effects of Acid Rain

Acid rain has detrimental effects on various ecosystems and materials:

  • Aquatic Ecosystems: Acidification of lakes and rivers can harm fish and other aquatic life.
  • Soil: Increased soil acidity can damage plant roots and affect nutrient availability.
  • Vegetation: Acid rain can damage leaves and reduce plant growth.
  • Materials: Acid rain can corrode buildings, statues, and other structures made of stone, metal, and other materials.

Chemical Reactions in Acid Rain Formation

Simplified chemical reactions involved in acid rain formation:

  • SO2 + H2O → H2SO3 (Sulfurous acid)
  • H2SO3 + 1/2 O2 → H2SO4 (Sulfuric acid)
  • NO2 + OH- → HNO3 (Nitric acid)

Ozone Layer Depletion

The Hole in the Ozone Layer

Studies have shown an increase in the size of the ozone hole, particularly over Antarctica, and its link to rising skin cancer rates and blindness in sheep in the Southern Hemisphere.

Role of NOx

  • NOx is produced naturally during thunderstorms.
  • Human-produced NOx from combustion generally doesn’t reach the stratosphere due to its reactivity in the troposphere.
  • Nitrous oxide (N2O), released from combustion and agricultural soil denitrification, is less reactive and can reach the stratosphere, where it converts to NOx through photolysis.
  • NO + O3 → NO2 + O2
  • NO2 + O → NO + O2
  • O + O2 → O3

Role of Chlorine Compounds

  • Chlorine compounds are released naturally from the ocean and volcanic eruptions, and artificially from sources like chlorofluorocarbons (CFCs).
  • These compounds can reach the stratosphere and break down ozone through a series of reactions.