Question

This satellite image shows a portion of the desert in northern Saudi Arabia, a region known for its abundant sunshine, high temperatures, and meager rainfall. The green circles are agricultural fields that are about 1 kilometer \((0.62\) mile \()\) in diameter. Water for irrigation is pumped from deep aquifers and distributed around a center point within each field-a technique known as center pivot irrigation. The deep aquifers contain water that dates to the Ice Age about 20,000 years ago, a time when the climate in this region was wetter and milder. a. Is it likely that agricultural activity in this region is sustainable indefinitely? Explain. b. A significant portion of the water placed on these fields is "lost" (not available to the crops). Suggest a reason for the loss of water. c. Relate what is likely occurring to the water table in the region pictured here to an example of a similar situation in the United States.

Short answer

The region's agricultural activity is not sustainable due to finite water resources. Water is lost mainly through evaporation. Similar depletion occurs in the Ogallala Aquifer in the US.

Step-by-step solution

Understanding Sustainability

Sustainability in agriculture refers to the ability to maintain agricultural practices over a long period. In this scenario, the water used for irrigation is being pumped from ancient aquifers, which are not replenished by modern rainfall. This implies that the water resource is finite and being depleted with use.

Evaluate Agricultural Activity Indefinitely

Since the aquifers contain water from the Ice Age and are not replenished, the continuous use of these water sources for agriculture implies that they will eventually run dry. Therefore, agricultural activity in the region cannot be sustained indefinitely without a reliable source of renewable water.

Water Loss Explanation

Water loss in agricultural fields often occurs through evaporation, especially in regions with high temperatures like northern Saudi Arabia. Additionally, some water can be lost through runoff or seepage beyond the root zone of the plants.

Relating to a Similar Situation in the US

In the United States, a similar situation can be observed in the High Plains Aquifer (Ogallala Aquifer) where groundwater is being depleted faster than it is recharged. This leads to a decrease in the water table, mirroring the scenario in northern Saudi Arabia where aquifer water is used for irrigation.

Key concepts

Center Pivot Irrigation

Center pivot irrigation is a modern agricultural technique used to water crops efficiently across large areas. The system involves a sprinkler device that rotates around a central pivot point. This method forms green, circular-shaped fields as seen from above, especially apparent in regions with limited water resources like the desert in northern Saudi Arabia.

• Functionality: The central pivot acts as the source, pumping water through pipes and spraying it over crops with specially placed sprinklers along the pivot's arms.
• Advantages: It is known for its efficient coverage, requiring less labor and reducing water wastage by targeting specific areas of crops.
• Challenges: Despite its efficiency, some water can still be lost due to evaporation and wind, especially in hot and arid climates where evaporation rates are high.

Center pivot irrigation is crucial in areas where agriculture faces challenging climates. However, it heavily relies on sustainable water sourcing to ensure long-term viability.

Water Table Depletion

Water table depletion is a critical concern in regions that rely on groundwater as the primary source of irrigation. The water table refers to the underground boundary between the soil surface saturated with water and soil that is not. In agricultural practices that use aquifers non-sustainably, the water table can decline significantly over time.

• Impact of Overuse: Pumping water faster than it is naturally replenished leads to a drop in the water table. This restricts the availability of water for future agricultural or human consumption.
• Signs of Depletion: Wells may run dry, and the amount of energy needed to pump water increases as it must be extracted from deeper levels.
• Environmental and Economic Consequences: Continuous depletion can lead to increased costs and reduced agricultural productivity.

Managing pumping rates and exploring alternative irrigation methods can help mitigate the effects of water table depletion.

Aquifers

Aquifers are natural underground reservoirs that store vast amounts of water. They serve as essential sources for irrigation, especially in arid regions where surface water is scarce. The water stored in deep aquifers, like those in northern Saudi Arabia, might be ancient, dating back thousands of years.

• Types of Aquifers: They can be classified as either confined or unconfined, depending on the presence of an impermeable barrier above or around the water-bearing area.
• Non-renewability: Some aquifers are not replenished by current rainfall, often termed as 'fossil' water sources. These are considered finite resources.
• Usage and Depletion: Continuous extraction can lead to aquifer depletion, affecting the water table and further stressing agricultural capabilities.

Efficient and careful management of aquifers is essential for sustaining agricultural activities and supporting broader water needs.