The disappearance of the Aral Sea, located between Kazakhstan and Uzbekistan, is widely known as one of the greatest ecological disasters caused by human hands. Starting in the 1960s, the diversion of the rivers that fed it to boost intensive Soviet cotton cultivation transformed the fourth largest lake in the world into an immense saline desert. However, the consequences go far beyond biodiversity loss or local geographic changes.
The climate impact. A study with a Spanish firm has put figures on a problem that goes far beyond desiccation, since the reality is that the dry bed of the Aral is a gigantic source of greenhouse gas emissions. And to put it in context, it has been seen that since the beginning of its desiccation has released about 748 million tons of CO₂a figure equivalent to the combined emissions of one year of Spain, France and Belgium.
The biological mechanism. Historically, arid areas transformed into crops through irrigation, as occurred in Central Asia, have been counted as carbon sinks. However, when crossing the cycle of these irrigations with the emissions of the lake that they dried to exist, the global balance is completely reversed in favor of the emission of greenhouse gases.
Something that we have repeated a lot is that lakes and wetlands act as natural sinks by retaining the atmospheric carbon that vegetation absorbs during photosynthesis, which ends up deposited and immobilized in the bottom sediments dragged by river networks. And now we are remembering this same mechanism.
The problem. The water column acts as a physical plug that isolates sediments from atmospheric oxygen, and when the water disappears, that plug disappears. This causes oxygen to quickly penetrate the sediment layers and trigger an immediate biological response: communities of lethargic microorganisms “wake up” and begin to degrade the organic matter that had accumulated for centuries. It is during this aerobic microbial degradation process that the massive release of carbon dioxide into the atmosphere that has been accumulating for many years occurs.
The Spanish team’s measurements corroborate this process, since, by analyzing sediments in a spatial gradient to the center of the wetland, the researchers verified that the most recently dried beds still retain a large amount of organic carbon compared to those that were exposed in the 1960s.
The solution. One of the most emphatic conclusions of the work is that the current mitigation strategies in the area are not working. Efforts to plant vegetation on the old dry bed have practically zero CO₂ absorption capacity in this type of arid ecosystems and are not providing any real solution.
For all this, the only way to stop microbial degradation and stop CO₂ emissions is to restore physical insulation, that is, cover the area again with water.
The data. Researchers estimate that some 605 million tons of CO₂ still remain to be released if no action is taken, and preventing this massive leak requires a monumental, but technically feasible, intervention. The problem that has been seen right now is that the area’s obsolete irrigation network wastes up to 90% of the water it transports.
That is why modernizing the entire infrastructure, which would require 8.5 billion euros, would allow us to recover around 50% of the original surface of the lake from 1960. And the result would benefit the entire planet.
The financing. For pay for a water engineering project of this magnitude, the authors of the research propose using the avoided emissions themselves as a bargaining chip. And if it is possible to flood the wetland again and stop the emission of those 605 million tons of CO₂, that amount could be transformed into marketable carbon credits. Calculations estimate that the project would generate some 323 million tons equivalent in credits, whose value in the international market would range between 3,100 and 15,800 million euros.
Images | Khusen Rustamov
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