Mustang Bayou

This project was implemented to provide an integrated evaluation of the physical, chemical and biological characteristics of Mustang Bayou. Assessment of the environmental quality of the bayou provided information for TCEQ to determine the status of the watershed and provide a baseline to aid in recognition of emerging problems and water quality trends. An additional goal of this project was to delineate the tidal and non-tidal segments of Mustang Bayou. Any data gathered from the tidal portion of the water body was submitted to TCEQ to supplement data being collected for use in developing assessments methodologies for tidal streams.

The Mustang Bayou watershed, with a drainage area slightly greater than 100 square miles, is located south of Houston in Brazoria County. The headwaters are located northeast of Fresno and extend southeast for approximately 30 miles where it flows into Chocolate Bay. The northern end of the watershed is comprised of mostly rural homesteads ranging in size from less than an acre to small ranchettes - majority of which rely upon on-site wastewater disposal systems. The City of Alvin is situated in the middle of the watershed and is serviced by a municipal collection system and waste water treatment facility. Downstream of Alvin are agricultural fields and pasture lands with occasional homesteads also relying on-site wastewater disposal systems.

USGS initiated water quality, stream habitat and biological monitoring in August 2004 and completed all data collection in August 2005. Analysis of the data revealed Mustang Bayou's mean DO concentrations dropped below the minimum criteria approximately 50 percent of the time, demonstrating a failure to fully support the assumed high aquatic-life use classification. Likewise, bacteria results frequently exceeded the state contact recreation standards in more than one-third of the samples collected. However, nutrients such as ammonia, nitrate plus nitrite, and phosphorus did not exceed state screening levels in any samples. Chlorophyll-a concentrations were also acceptable throughout the bayou.

Fifteen pesticide compounds (six herbicides and nine insecticides) were detected in the 24 water samples collected from Mustang Bayou. The most widely-used herbicide in the United States, Atrazine, was detected in every sample. However, the highest concentration of Atrazine was still less than half of the established Maximum Contamination Limits (MCL) for that compound. No organochlorine pesticides or PCBs were detected in the bayou sediments and concentrations of metals were below screening levels.

The stream habitat assessment found habitat characteristics to range from "limited to intermediate" at every sampling location on the bayou. The macroinvertebrate species comprising the benthic communities were widely distributed throughout the bayou. Some areas were limited while other areas had exceptional diversity. Fish communities also indicated a wide variety of aquatic life use. The bayou supported limited diversity and abundance in some areas while supporting exceptional numbers elsewhere.

See the full study here.  (PDF 4.13MB)

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