Human use of Earth’s natural resources is making the air, oceans, freshwaters, and soils more acidic, according to a U.S. Geological Survey — University of Virginia study available online in the journal, Applied Geochemistry. This comprehensive review, the first on this topic to date, found the mining and burning of coal, the mining and smelting of metal ores, and the use of nitrogen fertilizer are the major causes of chemical oxidation processes that end generate acid in the Earth-surface environment. These widespread activities have increased carbon dioxide in the atmosphere, increasing the relative acidity of oceans; produced acid rain that has increased the acidity of freshwater bodies and soils; produced drainage from mines that has increased the acidity of freshwater streams and groundwater; and added nitrogen to crop lands that has increased the acidity of soils.
Although there are many mechanisms of global acidification, the focus in this new study is on the major ones, including emissions from combustion of fossil fuels and smelting of ores, mining of coal and metal ores, and application of nitrogen fertilizer to soils.
These widespread activities have resulted in:
(1) Increased CO2 concentration in the atmosphere that acidifies the oceans;
(2) Acidic atmospheric deposition that acidifies soils and bodies of freshwater;
(3) Acid mine drainage that acidifies bodies of freshwater and groundwaters;
(4) Nitrification that acidifies soils.
There are natural geochemical reactions of mineral weathering and ion exchange work to buffer acidification, the slow reaction rates or the limited abundance of reactant phases are not enough. Relatively recent modifications of resource extraction and usage in some regions of the world have begun to ameliorate local acidification, but expanding use of resources in other regions is causing environmental acidification in previously unnoticed places. In other words, some countries try to reduce these effects while others are more eager to expand and develop.
"We believe that this study is the first attempt to assess all of the major human activities that are making Earth more acidic," said USGS scientist Karen Rice, who led the study. "We hope others will use this as a starting point for making scientific and management progress to preserve the atmosphere, waters, and soils that support human life."
To examine the global impact of acidification, the researchers developed a series of world maps to show current coal use, nutrient consumption, and copper production and smelting by country. By combining this information with the anticipated population growth through 2050 and the impact of changing technology, regulations and other factors, the researchers address shifting trends in acidification.
"Looking at these maps can help identify where the current hotspots are for producing acidity, The population increase map can help guide policymakers on possible future trends and areas to watch for the development of new hotspots." said Rice.
For example, the populations of some countries in Africa are projected to increase in the near future. To support the growing populations, these countries likely will be forced to apply more nitrogen fertilizer to their crops than they currently use, increasing the acidification of soils and freshwater resources in a region that had not previously been affected.
To look at the impact of the acid producing activities, the researchers characterized the scale of environmental damage from major activities and their components as local, regional, global, or some combination of the three. Generating power by burning coal, for instance, can have local, regional and global impacts. Locally, it can cause acid mine drainage where the coal is mined; regionally, burning it can cause acid rain; globally, the increased carbon dioxide in the atmosphere increases the acidity of the ocean.
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