Barbara J Mahler (Former Employee)

Four spring outlets of the Barton Springs system provide the only known habitat for the Barton Springs salamander (Eurycea sosorum), a federally listed endangered species. After heavy rainfall, sediment is flushed through the Barton Springs segment of the Edwards aquifer and springflow often becomes turbid (cloudy). Sediment in urban areas often has high concentrations of hydrophobic...

In spring 2000, the Texas Department of Health issued a fish consumption advisory for Lake Worth in Fort Worth, Texas, because of elevated concentrations of polychlorinated biphenyls (PCBs) in fish. In response to the advisory and in cooperation with the U.S. Air Force, the U.S. Geological Survey collected 21 surficial sediment samples and three gravity core sediment samples to assess...

The Arroyo Colorado, an ancient channel of the Rio Grande, extends 90 miles from Mission, Tex., to the Laguna Madre. The Arroyo Colorado flows through areas of intense agricultural cultivation and through important habitat for migrating birds and other wildlife, including several wildlife sanctuaries and refuges. The above-tidal segment of the Arroyo Colorado is included in the State of...

During 1999–2001, the U.S. Geological Survey, in cooperation with the Texas Natural Resource Conservation Commission, collected samples of untreated water from 48 public water-supply reservoirs and 174 public water-supply wells. The samples were analyzed for volatile organic compounds (VOCs) and soluble pesticides; in addition, well samples were analyzed for nitrite plus nitrate and...

Some fish in the Donna Canal contain PCBs at levels that might pose a risk to human health if the fish are eaten. Early attempts to locate the source of PCBs in the canal were unsuccessful. An innovative method of sampling and analyzing suspended sediment helped scientists detect PCBs in suspended sediment and narrowed the probable PCB source area(s) from the entire 11-kilometer canal to...

This study focuses on the coupled transport of dissolved constituents and particulates, from their infiltration on a karst plateau to their discharge from a karst spring and their arrival at a well in an alluvial plain. Particulate markers were identified and the transport of solids was characterised in situ in porous and karstic media, based on particle size analyses, SEM, and traces...