Lakes, Wetlands, and Glaciers: Types, Formation, and Human Impacts

Posted on Aug 15, 2024 in Geology

Large Bodies of Water: Lakes

Lakes are large bodies of water located on the surface of continents, characterized by varying degrees of salinity. Several factors influence a lake’s salinity:

  • Intense evaporation
  • Salt concentration of incoming water sources
  • Drainage from the watershed area
  • Presence of a seaward outlet

For instance, a lake experiencing high evaporation and receiving water with high salt content, or situated in a watershed with significant salt deposits, will likely have high salinity. Conversely, a lake with a seaward outlet and moderate evaporation will generally exhibit lower salinity.

Types of Lakes

Lakes are classified into various types based on their formation:

  • Glacial Lakes: Formed in depressions carved by glaciers or in valleys dammed by glacial moraines.
  • Volcanic Lakes: Found in craters of extinct volcanoes or calderas formed by volcanic explosions or collapses.
  • Karst Lakes: Occupy sinkholes created by the collapse of underground cavities in karst landscapes.
  • Tectonic Lakes: Originate in areas where the Earth’s crust has fractured and subsided, often found in rift valleys.

Lake Stratification and Mixing

The water column in a lake undergoes mixing processes that vary depending on the climate zone:

  • Warmer Regions: Strong stratification occurs during summer with a distinct thermocline (a layer of rapid temperature change). Autumn brings reduced sunlight and wind-induced turbulence, leading to incomplete mixing and a less defined thermocline. These lakes experience one annual mixing event (monomictic).
  • Temperate Regions: An ice layer forms during winter, preventing turbulence and vertical mixing. Spring melting allows surface water to reach 4°C, triggering mixing. Summer stratification develops again with a thermocline, followed by another mixing event in autumn. These lakes mix twice a year (dimictic).

Ponds and Wetlands

Ponds are smaller and shallower than lakes. Brackish lagoons often receive water influenced by saline aquifers. Coastal lagoons are seawater bodies partially isolated from the sea by barriers like reefs or sandbars.

Wetlands encompass marshes and plains where the water table intersects the land surface, creating a shallow, discontinuous water layer. They can also form from the isolation and drying of coastal lagoons, subsequently colonized by vegetation.

Glaciers: Earth’s Frozen Reservoirs

Glaciers, integral components of the cryosphere, store over two-thirds of Earth’s freshwater. The majority of glacial ice resides in ice caps covering Antarctica and Greenland, reaching thicknesses exceeding 4,000 meters. Alpine glaciers, found atop high mountains, have thinner ice cover.

Glacial Ice Formation

Glacial ice originates from compacted snow. The weight of accumulating layers, along with melting and recrystallization, transforms snow into denser forms:

  • Snow
  • Neve (Firn): Granular, compacted snow
  • White Ice: Further compacted with less air
  • Blue Ice: Extremely dense with minimal air, giving it a bluish hue and high clarity

Arctic and Antarctic Ice Sheets

The Arctic Ocean remains largely frozen year-round, forming a natural ice bridge connecting Asia, North America, and Greenland. This sea ice, primarily frozen seawater, expels salt during freezing, leading to lower salinity within the ice compared to the surrounding ocean. Global warming is causing a decline in sea ice extent.

Antarctica also features an extensive ice sheet, almost continental in size. This ice mass is also experiencing a shrinking trend due to global warming.

Human Impacts on the Hydrosphere

Human activities, particularly pollution and overexploitation, significantly impact the hydrosphere.

Pollution

Pollution alters the physical and chemical properties of water bodies, harming ecosystems and diminishing water resources.

Chemical Contaminants

  • Organic matter (untreated sewage, fertilizers, etc.) leads to eutrophication, depleting oxygen and harming aquatic life.
  • Heavy metals (lead, mercury) from industrial sources accumulate in the food chain, posing risks to organisms.

Physical Pollutants

  • Heat discharge from industries reduces dissolved oxygen levels.
  • Sonar from ships disrupts echolocation in marine animals.
  • Suspended solids increase turbidity, hindering photosynthesis in aquatic plants.

Biological Contaminants

  • Protozoa, viruses, and bacteria from untreated sewage pose health risks.

Overexploitation

Overexploitation occurs when water extraction exceeds the replenishment rate, leading to:

  • Reduced river flow, potentially falling below ecological requirements.
  • Shrinking or disappearance of lakes, ponds, and wetlands.
  • Loss of springs and seasonal watercourses.
  • Aquifer depletion and salinization.

These alterations degrade aquatic ecosystems and impact dependent species.

Water Pollution Indicators

Various indicators help assess water quality:

Chemical Indicators

  • BOD (Biochemical Oxygen Demand): Measures oxygen needed for microbial decomposition of organic matter.
  • COD (Chemical Oxygen Demand): Estimates oxygen required for chemical oxidation of organic matter.
  • Dissolved Oxygen: Measures oxygen concentration in water.
  • TOC (Total Organic Carbon): Measures carbon in organic compounds.
  • Nitrite and Nitrate Concentration: Indicate organic pollution and fertilizer runoff.
  • pH: Measures acidity or alkalinity.

Physical Indicators

  • Transparency: Turbidity indicates suspended solids.
  • Temperature: Increased temperature reduces oxygen solubility.
  • Color: Indicates dissolved substances.
  • Electrical Conductivity: Reflects dissolved salt content.

Biological Indicators

  • Presence of sensitive species: (e.g., certain insect larvae, trout) indicates good water quality.
  • Presence of tolerant species: (e.g., Tubifex worms) suggests pollution tolerance.
  • Algal blooms: Indicate nutrient enrichment (eutrophication).

Types of Water Pollution Sources

  • Point Source Pollution: Originates from a specific location (e.g., industrial discharge).
  • Diffuse Pollution: Occurs over a wide area (e.g., agricultural runoff).

Water Pollution Impacts and Remediation

Surface water pollution is generally easier to detect and remediate than groundwater pollution. Natural self-purification processes in rivers aid recovery.

Remediation Strategies

  • Aquifer Overexploitation: Artificial recharge through injection wells or infiltration basins.
  • Surface Water Overexploitation: Regulate water use, reduce demand, and restore natural flow regimes.
  • Pollution Impacts: Wastewater treatment, oil spill cleanup (containment, skimming, bioremediation), pH adjustment, aeration.

Conclusion

Protecting the hydrosphere requires a multifaceted approach, including reducing pollution, managing water resources sustainably, and addressing the impacts of climate change. Understanding the interconnectedness of Earth’s water systems is crucial for ensuring the health of aquatic ecosystems and the availability of clean water for future generations.