Category Water Science & Management

What is arsenic?

Millions of people all over the world are affected by the contamination of groundwater with arsenic. Most of them live in South Asian countries such as Bangladesh, Cambodia, India, Nepal and Vietnam.

 A study in 2017 revealed that over 60 million Pakistanis who live in the Indus River Valley are at risk from arsenic poisoning their drinking water.

Arsenic is a chemical element that has no odour or taste, making it difficult for a lay person to detect. Trace quantities of arsenic are essential in the human diet, but is dangerous in large amounts. Long-term exposure can lead to skin lesions, cancer, developmental defects, heart disease and diabetes.

While 10 mcg per litre is the safe limit recommended by WHO, in the Indus Valley, the concentration exceeded 200 mcg in many places!

Arsenic occurs naturally in the Earth’s crust, but it stays locked in the rocks and sediment. When people draw too much water from underground aquifers, it causes the water tables to drop drastically. The water deep down is often tainted by arsenic.

Picture Credit : Google 

What is fossil water?

Fossil water is the ancient freshwater that got trapped underground in huge reservoirs or aquifers. This water may have been locked in for over thousands of years and remain undisturbed. It can be found across the globe, be it in arid, semi-arid, humid regions, or even regions of permafrost.

Ever heard of fossil water? You may be aware of fossils. So going by the terminology of fossils, does fossil water mean that the water is really old?

Well, fossil water or petrowater or paleowater is the water that is trapped among the rocks underneath for millennia. It is the ancient freshwater that got trapped underground in a huge reservoirs or aquifer (a geological formation comprising an underground layer of porous rocks where water can be stored) in an undisturbed space.

One aquifer in Libya, has been carbon-dated to 40,000 years ago. It has only been a few decades since we started accessing fossil aquifers. In water-deprived areas and dry climates, these have become sources of water.

Presently, billions across the world are dependent on water from fossil aquifers for drinking as well as irrigation purposes.

Location and formation

Fossil water can be found across the globe, be it in arid, semi-arid, humid regions, or even regions of permafrost. An example of fossil water would be the Nubian Sandstone Aquifer System which is the biggest fossil aquifer in the world.

How and when did fossil water form? Fossil water formed during the last glacial ice age. Water got collected from melting ice and prehistoric lakes, as it seeped into the subterranean layers of rocks and sand in old aquifers.

As time went by, these got filled with sediment and thus got isolated, thereby sealing off the water from Earth’s surface. They remained there, unaffected and undisturbed for tens of thousands of years. But we don’t know how much of this water exists.

How sustainable is fossil water

Fossil water is trapped in layers of impermeable rocks and clay. As such they cannot absorb precipitation. So once depleted, they cannot be replenished easily.

Further, some pockets of fossil water are located in deserts and cannot be replenished due to the absence of enough annual precipitation. For instance, consider the Ogallala aquifer. Once it is fully mined, it is said that it would take over 6,000 years to replenish it.

Future of fossil water

The old groundwater is becoming an option in some water-strapped nations. If we continue extracting fossil water mindlessly, then the area’s water table goes down permanently.

As this water is non-renewable, there is always a risk of these aquifers going dry. Meanwhile, if it remains unaffected by human activities, then it can remain in equilibrium.

But can you drink ancient groundwater? Since this water has been around for thousands of years, like anything that has been around for millennia, this water would taste different too. Natural chemicals also get leached into it. They can be salty and contain contaminants such as iron and manganese. They need to be treated to be used for drinking purposes.

Picture Credit : Google 

WHAT IS A WATERSHED?

A river can originate from the end of a melting glacier or snow. It can also start from a lake or a spring. As it flows downstream, the river is joined by many tributaries, which increase its flow to make one large river. The land area that feeds, or drains into, a specific river and its tributaries is the watershed for that river system.

A watershed is an area of land that drains or “sheds” water into a specific waterbody. Every body of water has a watershed. Watersheds drain rainfall and snowmelt into streams and rivers. These smaller bodies of water flow into larger ones, including lakes, bays, and oceans. Gravity helps to guide the path that water takes across the landscape.

Not all rain or snow that falls on a watershed flows out in this way. Some seeps into the ground. It goes into underground reservoirs called aquifers. Other precipitation ends up on hard surfaces such as roads and parking lots, from which it may enter storm drains that feed into streams.

Watersheds can vary in size. A watershed for a tiny mountain creek might be as small as a few square meters. Some watersheds are enormous and usually encompass many smaller ones. The Mississippi River watershed is the biggest watershed in the United States, draining more than three million square kilometers (one million square miles) of land. The Mississippi River watershed stretches from the Appalachian Mountains in the east to the Rocky Mountains in the west. Thirty-one U.S. states and two Canadian provinces fall within the Mississippi River watershed.

Credit: National Geographic Society

Picture Credit : Google