Reservoirs Affect the Movement of Carbon in Large Rivers of the Central and Western United States plus 1 more |
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Reservoirs Affect the Movement of Carbon in Large Rivers of the Central and Western United States Posted: 16 Jun 2014 09:47 AM PDT
Summary: A recent study conducted by scientists from the U.S. Geological Survey and published in the Journal of Geophysical Research – Biogeosciences found that a combination of climate and human activities (diversion and reservoirs) controls the movement of carbon in two large western river basins, the Colorado and the Missouri Rivers
Contact Information: Heidi Koontz ( Phone: 303-202-4763 ); A recent study conducted by scientists from the U.S. Geological Survey and published in the Journal of Geophysical Research – Biogeosciences found that a combination of climate and human activities (diversion and reservoirs) controls the movement of carbon in two large western river basins, the Colorado and the Missouri Rivers. Rivers move large amounts of carbon downstream to the oceans. Developing a better understanding of the factors that control the transport of carbon in rivers is an important component of global carbon cycling research. The study is a product of the USGS John Wesley Powell Center for Analysis and Synthesis and the USGS Land Carbon program. Different downstream patterns were found between the two river systems. The amount of carbon steadily increased down the Missouri River from headwaters to its confluence with the Mississippi River, but decreased in the lower Colorado River. The differences were attributed to less precipitation, greater evaporation, and the diversion of water for human activities on the Colorado River. For upstream/headwater sites on both rivers, carbon fluxes varied along with seasonal precipitation and temperature changes. There was also greater variability in the amount of carbon at upstream sites, likely because of seasonal inputs of organic material to the rivers. Reservoirs disrupted the connection between the watershed and the river, causing carbon amounts downstream of dams to be less variable in time and less responsive to seasonal temperature and precipitation changes. The study presents estimates of changes in the amount of carbon moving down the Colorado and Missouri Rivers and provides new insights into aquatic carbon cycling in arid and semi-arid regions of the central and western U.S, where freshwater carbon cycling studies have been less common. This work is part of an ongoing effort to directly address the importance of freshwater ecosystems in the context of the broader carbon cycle. In the future, changing hydrology and warming temperatures will increase the importance of reservoirs in carbon cycling, and may lead to an increase in Greenhouse Gas Emissions that contribute to global warming, but may also increase the amount of carbon buried in sediments. |
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Austin Coal-Tar Sealant Ban Leads to Decline in PAHs Posted: 16 Jun 2014 08:00 AM PDT
Summary: The 2006 prohibition on the use of coal-tar-based pavement sealants in Austin, Texas, has resulted in a substantial reduction in polycyclic aromatic hydrocarbons (PAHs), according to a new study by the U.S. Geological Survey
Contact Information: Peter Van Metre ( Phone: 512-927-3506 ); Jennifer LaVista ( Phone: 303-202-4764 ); The 2006 prohibition on the use of coal-tar-based pavement sealants in Austin, Texas, has resulted in a substantial reduction in polycyclic aromatic hydrocarbons (PAHs), according to a new study by the U.S. Geological Survey. Pavement sealant is a black, shiny substance sprayed or painted on the asphalt pavement of parking lots, driveways and playgrounds to increase the longevity of the underlying asphalt pavement and enhance its appearance. Pavement sealants that contain coal tar have extremely high levels of PAHs compared to asphalt-based pavement sealants and other urban PAH sources such as vehicle emissions, used motor oil and tire particles. PAHs are an environmental health concern because several are probable human carcinogens and they are toxic to fish and other aquatic life. In 2006, Austin became the first jurisdiction in the United States to ban the use of coal-tar sealants. USGS scientists evaluated the effect of the ban on PAH concentrations in lake sediments by analyzing trends in PAHs in sediment cores and surficial bottom sediments collected in 1998, 2000, 2001, 2012 and 2014 from Lady Bird Lake, a reservoir on the Colorado River in central Austin. Average PAH concentrations in the lower part of the lake have declined 58 percent since the ban, reversing a 40-year upward trend. The full study, reported in the scientific journal Environmental Science and Technology, is available online. “Identifying contaminant trends in water and sediment is key to evaluating the effect of environmental regulations, and provides vital information for resource managers and the public,” said lead USGS scientist Dr. Peter Van Metre. Results of the USGS study support the conclusions of previous studies that coal-tar sealants are a major source of PAHs to Lady Bird Lake and to other lakes in commercial and residential settings. A sediment core collected by the USGS from Lady Bird Lake in 1998 was part of a study of 40 lakes from across the United States that used chemical fingerprinting to determine that coal-tar sealants were, on average, the largest contributor of PAH to the lakes studied. Chemical fingerprinting of sediment collected for the new study indicates that coal-tar-based sealant continues to be the largest source of PAHs to Lady Bird Lake sediment, implying that PAH concentrations should continue to decrease as existing coal-tar-sealant stocks are depleted. To learn more, visit the USGS website on PAHs and sealcoat. |
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