Geochemistry of bottom sediments -- Matagorda Bay system, Texas

Approximately 800 sediment samples from stream beds and bay bottoms of water bodies that compose the Matagorda Bay system were collected and analyzed. Shell-sand-mud ratios and total organic carbon content were determined, and 20 trace elements were detected. In general, highest concentrations of trace elements coincide with deep areas of- water bodies, areas of mud accumulation, and areas with high total organic carbon content. Zirconium, calcium, strontium, and mercury do not follow the distribution patterns of most other elements. Zirconium (Zr) is concentrated in sand located chiefly along bay margins and in tidal deltas; high Zr values result from the physical concentration of zircons as heavy mineral placers associated with sand bodies. Calcium and strontium distributions coincide with distribution of shell material. Mercury distribution is restricted to Lavaca Bay and northwestern Matagorda Bay. When concentrations of 20 trace metals in the Matagorda Bay system are compared with concentrations of elements in the crust, shale or clay, and seawater, it is found that (1) Matagorda Bay sediment contains trace elements in about the same concentrations as crustal rocks and shale but exhibits concentrations higher than seawater, and (2) only two elements, boron and mercury, identified within bay-system sediment exhibited anomalously high concentrations. These high concentrations are believed to result from man's activities within the Texas Coastal Zone.