Lsotopic dating techniques may be used to help monitor surface water pollution

Recently, the Chinese Academy of Sciences Institute of Geographic Sciences and Resources, deputy researcher Han Dongmei team through the system to collect the nationwide massive survey data, China's groundwater nitrate pollution, water organic pollution conducted a comprehensive analysis and evaluation.

The results show that the nitrate pollution in the groundwater of the coastal area, especially the coastal karst area is much higher than that in the inland areas. Nitrogen isotope contamination traces indicate that, in addition to agricultural fertilization, soil nitrogen and domestic wastewater discharge is also an important factor affecting the distribution of nitrate in groundwater.

Contains a lot of nitrate water, in the human body can be reduced to nitrite poisoning, or produce carcinogenic, teratogenic, mutagenic substances. "Groundwater radioactive carbon testing can be used as a tool to monitor the over-exploitation of subsurface aquifers to prevent the aquifers from being polluted or over-exploited." Han Dongmei said.

Isotope as an important means of water cycle and water system research, with the test technology and simulation methods continue to develop, its scope of application is growing. Recently, the 2017 isotope hydrological and eco-environmental applications seminar, experts on the different applications of isotopes have expressed their views, concern or groundwater pollution problems, "the face of groundwater pollution, especially the composite pollution source identification, isotope technology more and more important". Department of Environmental Protection Planning Institute of groundwater and drinking water source protection room director Liu Weijiang said.

Groundwater radioactive carbon dating

Different isotopes have different applications. Stable isotopes play a role in the field of precipitation-surface water-groundwater interactions, environmental solute transport, and biogeochemical cycles. Radioactive isotopes play an important role in the dating of water bodies such as ice cores, groundwater, and ocean currents effect.

Groundwater radioactive carbon dating can indicate that groundwater stops direct contact with other substances such as air, for example, it can indicate when water flows into the ground. Surface water and rainfall from the air to absorb a small amount of carbon dioxide into the ground. After leaving the atmosphere, the water begins to touch the soil gas, where the respiration of the plant roots produces much higher carbon dioxide. Qin Dajun, an associate researcher at the Institute of Geology and Geophysics, Chinese Academy of Sciences, points out that radioactive carbon in these sources is known as the "modern" level and can be used as a reference in age calculations.

By extracting carbonates from water for radioactive carbon dating, the measurements can provide information about groundwater sedimentation and water flow and frequency. If the aquifer contains fossil carbon, such as peat or lignite, then radioactive carbon dating may appear ambiguous results, and these aquifers are not suitable for the use of radioactive carbon dating this method to continue to study.

"Water from the surface can provide useful visual 'age', but there is an unavoidable problem, that is, carbon dilution correction." Qin Dajun explained that because in water, carbon dioxide under pressure is easy to form a bubble And the isotopic effect. In this case, we can not calculate a "best expected age".

Reveal aquifer pollution

With the increase in population density, people's demand for aquifers will also increase exponentially. However, over-exploitation will eventually lead to inadequate water supply, especially in areas far from the aquifer recharge area, with greater impact.

Due to population aggregation, housing and industrial development are as far as possible to the highest industrial output direction. However, if the development area invades the supply area, a new well that meets the urgent need is likely to cause a water supply shortage when the pumping exceeds the supply.

BETA (a monitoring company) official website, radioactive carbon dating and groundwater column gives a solution, by regularly monitoring a region of the water system of water radioactive carbon age, scientists can obtain experimental evidence, so that developers realize that excessive Development, to avoid out of control. Once the house or industry has been built, it would be very difficult to limit its water supply. The radioactive carbon dating of water can provide a mechanism for monitoring, understanding and controlling the exploitation of aquifers.

Carbon elements to express the amount of groundwater recharge, tritium elements can reveal the groundwater pollution. The World Health Organization's official website of the "drinking water quality guidelines" said that in nature there may be a very small amount of tritium. However, tritium is detected in water sources, which means potential industrial pollution.

According to a recent paper published in the "Nature - Earth Science", groundwater extraction, providing 40% of global agricultural irrigation and billions of people drinking. Global groundwater reserves are more than 100 times the total amount of water on all the lakes on Earth.

Researchers have detected more than 6,000 wells in the world, including groundwater that is not more than a kilometer deep in the formation. They detected trace amounts of tritium in more than half of the wells. This means that, although the ancient groundwater buried in the ground, it is not as people previously thought that from the human society pollution.

The paper also describes another bad news, deep in the formation, has been stored more than 12,000 years of paleo-groundwater, may also be a human society pollution.

Provide the basis for reverse inference

Tritium is a radioactive isotope of hydrogen, also known as artificial nuclide, which is a fission product of nuclear power reactors and nuclear weapons tests. According to reports, after the 1950s, many countries in the world of thermonuclear tests, such as nuclear bomb test, the release of a large number of tritium, resulting in natural precipitation tritium content increased by 5 times, or even 500 times. "Because of such a significant change, tritium is the ideal tracer to study the groundwater cycle," Qin said.

The half-life of tritium is only about 12 years, so the "age" of up to 1.2 million years of paleoclimatic water, theoretically, even if it contains tritium, its content should be very low and can not be detected. Therefore, once the detection of tritium in the ancient groundwater, these tritium may be from the ground in recent years, precipitation. Is the ground precipitation, the artificial release of tritium from the ground to the ancient groundwater. There is tritium, there will be other pollutants. And because of the deep formation, these pollutants may be in the ancient groundwater for a long time, may reach thousands of years.