Parental Smoking Cessation to Protect Young Children:A Systematic Review and Meta-analysis

RECHARGING THE WELL: How long can one pump water from an aquifer before it runs dry? The question seems a bit like a high school math problem, but the answers are not known and the implications are enormous. Aquifers are wet underground layers of rock or sediments from which water can be extracted by a well. For years, scientists have not had a good way to measure how fast aquifers are recharged by surface water. Commonly used dating tools, such as carbon 14, have been useful in archeology but not so much in understanding the flow of underground water. Now scientists have reported a breakthrough in dating technology using krypton 81. As reported in The New York Times (Science: November 21, 2011), krypton 81 is an isotope present in air. Once trapped underground in water that no longer has contact with air, krypton 81 begins to decay by a factor of two every 230,000 years. Capturing krypton 81 is extremely challenging as there is only one molecule of krypton 81 for every quintillion (10) water molecules. Using sophisticated technology, scientists were able to capture and measure krypton 81 in water samples obtained from deep in the Nubian Aquifer. The results suggest that the Nubian Aquifer has been collecting water for millions of years. The bad news is that the aquifer probably only recharges a little each year; thus, under normal circumstances the water level may only rise a few millimeters a year. While the aquifer still contains a massive amount of water, it is shared by four countries: Egypt, Libya, Chad, and Sudan. Rapid or heavy pumping could lead to both local and international conflicts. Already, some lakes and oases supplied by the aquifer are now dry. While water management is often a political rather than scientific issue, better understanding of the hydrology may make it easier to develop and adhere to water management plans.