Sediment Quality Triad Assessment of the Armand Bayou Watershed
Dingman, Charles F. and Cynthia L. Howard
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The Armand Bayou watershed is located on the western edge of Galveston Bay, north of Clear Lake, and includes extensive residential and industrial development and the 2,500_acre Armand Bayou Nature Center. Three primary streams comprise the watershed: Armand Bayou, Horsepen Bayou and Mud Lake. Although Armand Bayou is a designated Coastal Preserve, it is listed as an impaired water by the USEPA. Parameters of concern for TMDLs in Armand Bayou include organic enrichment, low dissolved oxygen and pathogens. Horsepen Bayou has not been evaluated for the EPA listing of impaired waters. Contaminants entering estuarine waters, such as the Armand Bayou system, often are deposited in the sediments. Analyzing sediments for target contaminants, such as heavy metals, inorganic compounds, pesticides and PCBs, is a useful way to evaluate the impact pollution in a specific location. However, sediment-bound contaminants may not always be bioavailable (i.e., harmful) due to their chemical or physical associations with the sediments, and a number of studies have shown that toxicity cannot be accurately predicted using analytical chemical analysis of the sediments alone. The Sediment Quality Triad (SQT) approach was developed to determine more accurately the degree to which contaminants are responsible for the degradation of sediment health. The SQT three components: sediment chemistry, sediment toxicity tests, and in situ benthic community parameters. The SQT approach was used for this study to identify areas in the Armand Bayou system where sediment contamination may be linked to ecosystem degradation and to evaluate the system with respect to TMDLs and proposed sediment quality guidelines.