RESTON, VA, June 16, 2014 -- According to a new study by the U.S. Geological Survey (USGS), a variety of human activities has contributed to elevated concentrations of dissolved solids, a measure of the salt content in water, in many streams across the nation.
The study determined that in about 13 percent of U.S. streams, concentrations of dissolved solids likely exceed 500 mg/L, which is the Environmental Protection Agency's (EPA) secondary, non-enforceable drinking water standard. Many of these streams are found in a north-south oriented band stretching from west Texas to North Dakota.
Accordingly, widespread occurrences of moderate concentrations are found in streams extending in an arc from eastern Texas to northern Minnesota to eastern Ohio, and low concentrations are found in many states along the Atlantic coast and in the Pacific Northwest.
The total amount of dissolved solids delivered to all streams is about 270 million metric tons annually, of which about 71 percent comes from weathering of rocks and soil, 14 percent from application of road de-icers, 10 percent from activities on agricultural lands, and 5 percent from activities on urban lands.
"For years we have known that activities, such as road de-icing, irrigation and other activities in urban and agricultural lands, increase the dissolved solids concentrations above natural levels caused by rock weathering," said William Werkheiser, USGS associate director for water, "and now we have improved science-based information on the primary sources of dissolved-solids in the nation's streams."
All water naturally contains dissolved solids as a result of weathering processes in rocks and soils. Some amount of dissolved solids is necessary for agricultural, domestic and industrial water uses and for plant and animal growth, and many of the major ions are essential to life and provide vital nutritional functions. Elevated concentrations, however, can cause environmental and economic damages.
As such, an online, interactive decision support system provides easy access to the national-scale model describing how streams receive and transport dissolved solids from human sources and weathering of geologic materials. The decision support system can be used to evaluate combinations of reduction scenarios that target one or multiple sources and see the change in the amount of dissolved solids transported downstream waters.
The dissolved-solids model was developed by the USGS National Water-Quality Assessment Program, which provides information about water-quality conditions and how natural features and human activities affect those conditions. Information on modeling applications, data and documentation can be accessed online.
"This study applied statistical modeling to understand the sources and transport processes leading to dissolved-solids concentrations observed in field measurements at over 2,500 water-quality monitoring sites across the nation," said David Anning, USGS lead scientist for the study. "This new information was then used to estimate contributions from different dissolved-solids sources and the resulting concentrations in unmonitored streams, thereby providing a complete assessment of the nation's streams."
See also:
"U.S. stream quality degraded by flow modifications, contaminants, says report"
"USGS report examines status of groundwater quality"
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