The role of organic carbon, iron, and aluminum oxyhydroxides as trace metal carriers: Comparison between the Trinity River and the Trinity River Estuary (Galveston Bay, Texas)




Wen, L-S
Warnken, KW
Santschi, PH

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Concentrations of many trace elements in aquatic systems can become enriched due to anthropogenic as well as natural processes. In order to investigate particle enrichment processes from the river through an estuary, the changes in solid phase speciation and particle-water partitioning of a number of trace metals (e.g., Fe, Pb, Cd, Cu, Ni, Zn, Co, V) were evaluated from the Trinity River through Galveston Bay to the Ocean. An established way to detect anthropogenic contamination is by normalization of contaminant concentrations to Fe, Al, and or organic carbon (OC). Particulate metal (Mn, Co, Ni, Cu, Pb, V, Ni, Zn, Cd) to Fe, Al, and metal to OC ratios were determined in waters of the Trinity River and Galveston Bay, in order to test 1) if the system is contaminated, and 2) whether Fe, Al, or organic carbon act as a master variable for determining metal concentrations. All particulate trace metals from Trinity River were present in ratios to Fe or Al similar to those from drainage basin soils, which were similar to world world-average soil. As expected, concentrations of Fe, Al and OC in particles from both the Trinity River as well as Galveston Bay were strongly correlated, from which one might conclude that Fe can be used as a reference element that is representative for all three of them. However, ratios to Fe of particle-reactive elements, such as Pb, were found to be significantly and positively correlated to the Fe content of particles from Galveston Bay, while nutrient-type elements, such as Cu, Ni, and Cd, were negatively correlated to their Fe content. Interestingly, suspended particles from the Trinity River did not exhibit any such correlations at all and only varied within a very limited range. The reason for such distinctive correlative behavior that distinguishes riverine from estuarine particles is likely caused by internal cycling of these elements within Galveston Bay, and their relationship to OC. Relationships of trace metals to OC revealed that differences in sources and cycling of OC in the estuary significantly altered the soil imprinted particle make-up. Results from selective leaching experiments of suspended particles in Galveston Bay confirmed the selective enrichment and fractionation processes for the different metals.


pgs. 20-37


aluminum oxyhydroxides, iron oxyhydroxides, organic carbon, trace metals