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Low flow at Barton Springs threatens endangered salamander

Friday, August 21, 2009 by Bill McCann

The prolonged drought is a serious threat to the endangered Barton Springs Salamander, according to a city staff expert.


“I’m very concerned, but cautiously optimistic that it will rain,” Laurie Dries, biologist at the Watershed Protection Department, told In Fact Daily.


The latest salamander count on Aug. 13 found only 35 salamanders at Eliza Spring near the Barton Springs Pool, Dries said. The average number of salamanders found monthly at Eliza Spring in the first six months of 2009 was 149, she said. In comparison, the annual average number in 2008 was 703.


The Barton Springs Salamander, which grows to about 2.5 inches in length, is known only to live in the environs of Barton Springs. It was identified as a separate species of salamander in 1993 and added to the federal endangered species list in 1997. Before 2003, the annual average of salamanders found was only 9 to 12 at Eliza Spring. But the numbers increased significantly after the city carried out a habitat restoration program.


Eliza Spring is considered the benchmark for the health of the salamander and typically has the highest salamander numbers. At another nearby spring at the Sunken Garden, no salamanders have been sighted in more than a year, Dries said. The number of salamanders at the Sunken Garden has typically been low, with the highest count in past years of only 70, she said.


A particular concern is that very few juvenile salamanders have been found in the most recent count at Eliza Spring, indicating that they are not reproducing, Dries said.


In a drought, dissolved oxygen levels in the water drop as discharges from the springs decrease. Studies of a related species, the San Marcos Salamander, showed that the growth rate of juvenile salamanders is impaired when the dissolved oxygen level drops to 4.4 milligrams per liter, she said. Other studies of adult San Marcos salamanders showed that the mortality rate increases slightly at 3.9 milligrams per liter. 


Last month dissolved oxygen dropped to below 4 milligrams per liter at Eliza Spring. Staff responded by operating a submersible pump to help aerate the water and increase the oxygen levels, according to Dries.


“We are doing everything we can, but we can’t make it rain,” Dries said.


Dries joined David Johns, hydrogeologist at the Watershed Protection Department, in reporting on the water quality of Barton Springs to the Environmental Board Wednesday. The report was an update of assessments conducted in 2000 and 2005. The latest update shows that water quality of the springs has degraded over time for several parameters, including dissolved oxygen, bacteria, nitrate-nitrogen and temperature, according to Johns. The degradation was not evident in the 2000 assessment. The latest results are similar to the 2005 assessment, although nitrate continued to increase, he said. Levels of E. coli bacteria continue to remain well below the state standard for recreation, he added.


On the water quantity side, the current flow of the springs is about 15 cubic feet per second, compared to the long-term average flow of 53 cubic feet per second, Johns said. The record low flow was 9.6 cubic feet per second in 1956 during the drought of record.

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