Episode 129: Glaciers, Ice, and Groundwater

Water Cycle

The water cycle, or hydrological cycle, describes the continuous movement of water on, above, and below the Earth's surface. James Fodor explains that the largest reservoir of water is the ocean, containing about 97% of Earth's water, while glaciers hold most of the freshwater. Groundwater, which makes up about 1-2% of Earth's water, is another significant reservoir 1. Precipitation, including rain and snow, plays a crucial role in connecting these reservoirs, with about 80% occurring over the ocean and 20% over land 1. Surface runoff and infiltration are key processes that move water from the surface into the ground, contributing to groundwater 2.

The continual recycling of the water content of Earth, which overall doesn't change very much, just kind of moves around.

--- James Fodor

Transpiration, a biological process where water vapor is released from plant pores, combines with evaporation to form evapotranspiration, returning water to the atmosphere 2.

   

Aquifers

Groundwater is water found beneath the Earth's surface in rock or soil pore spaces. James Fodor explains that groundwater is divided into the saturated zone, where all pore spaces are filled with water, and the unsaturated zone, where only some pore spaces contain water 3. The boundary between these zones is the water table, which marks the start of the saturated zone. Aquifers are underground layers of water-bearing permeable rock or sediment, from which groundwater can be extracted using wells 3.

Groundwater from aquifers can be extracted using a well. So that's what wells are for, right?

--- James Fodor

The pressure in the saturated zone is greater than atmospheric pressure, while in the unsaturated zone, it is less 3.

   

Recharge

Groundwater recharge involves the process of water infiltrating from the surface into the ground, eventually reaching greater depths through percolation. James Fodor describes how groundwater can be used by humans, extracted by plant roots, or eventually flow out to the ocean 4. This movement is driven by gravity and the energy of the sun, which evaporates water and returns it to the atmosphere, continuing the cycle 4.

The energy of the sun evaporates it and returns it to the clouds, where it can then move around and precipitate on the land.

--- James Fodor

Groundwater recharge is essential for maintaining the balance of the hydrological cycle and ensuring a sustainable supply of groundwater 4.

   

Challenges

Groundwater faces several challenges, including depletion, pollution, and seawater intrusion. James Fodor warns that over-extraction of groundwater can lower the water table, causing subsidence and even sinkholes 5. Pollution from improper waste disposal can contaminate groundwater, making it difficult to clean up. Seawater intrusion occurs when excessive groundwater extraction reduces pressure, allowing seawater to infiltrate aquifers 5.

If you dig too greedily and too deep, you can pump out too much water from the aquifer, which can result in the water table lowering.

--- James Fodor

Groundwater depletion is a significant problem, especially in areas with high withdrawal rates and low recharge 5.