Term Project Outline

CE 394K Surface Water Hydrology
University of Texas at Austin

Austin's Bat Population and Its Effect on

Water Quality in Town Lake

by J. Andrew Tachovsky


From approximately March to November, Austin is home to a sizable bat population. These bats have made their roost under the Congress Street bridge crossing Town Lake near the Austin-American Statesman Building. During the late summer months when dry weather prevails, observers can be seen by the bridge watching the bats as they begin their daily nocturnal rounds to feed on insects. As the bats have chosen to roost under a major structure crossing a segment of the Colorado River, it is hypothesized that the activities of the bats has an effect on the water quality in the Colorado.


The purpose of this project is to investigate the impact of the bats on the water quality of the Town Lake segment of the Colorado River. Water samples will be collected in small spatial increments and analyzed for nitrate, sulfate, phosphate, pH and dissolved oxygen (DO). Several sampling events will occur to monitor the effects as the bat population slowly departs for Mexico during the late fall and early winter.

Scope and Rationale:

The rationale for this project is based on the potential effects of nitrates in water. At low concentrations (less than 40 ppm) nitrates in surface water can cause plant growth and depression in pH. If these conditions are not corrected, eutrophication of surface water can occur leading to septic conditions and fish kills.

At high concentrations (above 44 ppm) nitrates in drinking water can cause health effects in humans. High nitrate concentrations in drinking water has been documented to cause difficulties with prenatal infants, and young children. Accordingly, nitrate concentrations above 44 ppm is considered unsafe.

Sulfate and phosphate concentrations will be measured as an indication of available nutrients for microbial activity. Depletion of these nutrients downstream indicates utilization by plant and microbial sources.


Three sampling events will be conducted. A canoe will be obtained and taken out to Town Lake. A picnic will be enjoyed, and a frisbee will be thrown. Sunbathing may take place. Three sampling events will be taken upstream from the bridge to determine background levels of nitrate, phosphate and sulfate. Samples will then be taken approximately every 15 feet starting under the bridge and continuing downstream approximately 200 yards. Zero headspace sampling technique will be used to assure sustained quality of samples.

Samples will be analyzed for pH and DO using appropriate membrane analysis techniques. Samples will be analyzed for nitrate, sulfate, and phosphate using Ion Cromatographic Analysis EPA SW 846 Method 9056.

Data and Expected Results:

It is expected that the Congress Street bridge will mark a region of increased nitrate and phosphate in surface water as a result of bat activity. It is also expected that DO will depleted as a result of increased plant and microbial activity in the water. However, It is expected that these abnormal conditions will dissipate with distance downstream from the bridge.

Sources of Information:

The data that is used in this project will be generated through the sampling events that have been described. A background literature review will be conducted to accurately describe the eutrophication and human health effects associated with increased nitrate in surface water.

If you like the sound of this project and would like to discuss it further, please contact:

J. Andrew Tachovsky
ja_tachovsky@ mail.utexas.edu

Return to the Course Home Page