Thursday, December 10, 2015

New Map of Earth's Groundwater Supply

[Live Science] A new map of Earth's groundwater supply shows where on the planet water is locked up and "hidden" underground.  
The map — the first of its kind — provides a visual representation of Earth's groundwater resources and estimates that the planet's total groundwater supply stands at approximately 5.5 million cubic miles (about 23 million cubic kilometers).
Groundwater is the source of the world's second-largest collection of freshwater, according to the National Ground Water Association. (The planet's primary source of fresh water comes from glaciers and ice caps.) Groundwater is collected from rainfall that seeps underground into aquifers and reservoirs beneath the land surface, according to the U.S. Environmental Protection Agency (EPA). [Earth in the Balance: 7 Crucial Tipping Points]
Groundwater is important for energy and food security, human health and healthy ecosystems, but it's also a resource that is at risk from overuse and human pollution, researchers said in a new study published online Nov. 16 in the journal Nature Geoscience.
The scientists obtained measurements of tritium, a radioactive version of the hydrogen molecule, and water flow models that used properties of water and its interaction with different types of rock to estimate how much groundwater the world possesses, where it is distributed and the age of the water in these underground reservoirs.
The researchers calculated that of the 5.5 million cubic miles of total groundwater in the uppermost 1.2 miles (2 km) of the continental crust, only between 24,000 to 129,500 cubic miles (100,000 to 540,000 cubic km) is young (modern) groundwater, which is less than 100 years old.
But, why is it important to know the age of groundwater? It turns out that young and old groundwater are fundamentally different in how they interact with the rest of the water and climate cycle, according to the study. Read More