February 2010, Vol. 22, No. 2


Elevated Chloride Levels Found in Urban Waterways

Urban streams and groundwater across the northern United States contain elevated levels of chloride, according to a study by the U.S. Geological Survey (USGS).

Elevated chloride levels can inhibit plant growth, as well as harm reproduction and reduce the diversity of organisms in streams, according to a USGS news release. To protect against this, federal criteria on chloride levels have been set. However, USGS found that more than 40% of urban streams tested exceeded this level.

Sources of chloride include road deicing, septic systems, wastewater treatment facilities, water softening, animal waste, fertilizers, landfill discharge, salt and brine in geologic deposits, and precipitation, the news release says.

The study examined chloride concentrations in parts of 19 northern states and included 1329 wells and 100 streams. Chloride yields were higher in cities than in farmlands and forests. Urban streams carried 31 Mg/km2 (88 ton/mi2) of chloride, compared to forest streams that carried about 2 Mg/km2 (6 ton/mi2) of chloride, according to the study. In urban streams, the highest levels of chloride, reaching 4000 ppm — approximately 20 times higher than the recommended federal criteria — were measured during winter months.

Deicing roads was determined to be the major cause of chloride in urban waters, according to the news release. “These findings are not surprising, but rather remind us of the unintended consequences that salt use for deicing may have on our waters,” said Matthew C. Larsen, USGS associate director for water. “Transportation officials continue to implement innovative alternatives that reduce salt use without compromising safety.”

The amount of chloride in these urban waters increased during the last two decades, which is consistent with an increase in salt use for deicing and expansion of roads and parking lots, in addition to the increase in septic systems, wastewater discharge, and landfills, which all contribute to chloride concentrations, the news release says.



Idaho Department of Water Resources Develops Satellite Water-Use Maps

As the demand for water resources climbs with increasing population and agricultural irrigation demands, the focus has turned to effective water management. Fortunately, in some areas, managing local water resources just became a little easier, thanks to a collaboration of several research organizations using satellite imagery

Using Landsat imagery supplied by the U.S. Geological Survey (USGS) in combination with ground-based water data, the Idaho Department of Water Resources (IDWR) and the University of Idaho (Moscow) developed a new method to create water-use maps, according to a USGS news release. This method can be as much as 80% more accurate than traditional measurement methods.

The method, a computer model called Mapping Evapotranspiration at High Resolution with Internalized Calibration, or METRIC, estimates and maps water use in vegetative areas, the news release says. IDWR and the University of Idaho, with initial assistance from NASA, began developing this model in 2000.

Now, Montana, California, New Mexico, Utah, Wyoming, Texas, Nebraska, Colorado, Nevada, and Oregon have adopted this mapping method.

The model monitors evapotranspiration — water transpired from plants and evaporated from land surfaces — and can zero in on an area the size of a field of crops to represent the amount of water consumed by irrigated agriculture and other land uses, according to an IDWR news release.

The model assists with negotiating water rights, assessing urban water transfers, managing aquifer depletion, monitoring water rights compliance, and protecting endangered species. It also can increase the accuracy and effectiveness of public decisions concerning water, something especially useful in dry areas where irrigation accounts for most water consumption.

In addition, Spain, South Africa, and Morocco have begun to use Landsat-based water-use maps, the USGS news release says. The USGS Landsat archive of satellite imagery dates back to 1972 and provides a source of consistent data on land surface water conditions, explained Bryant Cramer, USGS associate director for geography. “This advance by the Idaho water monitoring team is both brilliant and practical,” he said in the news release. “Looking forward, it’s indicative of what researchers in many countries can accomplish with the data.”


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