POLLUTION IN AN URBAN BAYOU: MAGNITUDE, SPATIAL DISTRIBUTION AND ORIGIN J. LIEBENS 1,3,∗ , C. J. MOHRHERR 2 , K. R. RAO 2 and C. A. HOUSER 1 1 Department of Environmental Studies, University of West Florida; 2 Center for Environmental Diagnostics and Bioremediation, University of West Florida; 3 Department of Environmental Studies, University of West Florida, 11000 University Parkway, Pensacola, FL 32514. ( ∗ author for correspondence, e-mail: Liebens@uwf.edu; Tel: (850)4742065; Fax: (850)8576036) (Received 22 June 2005; accepted 27 January 2006) Abstract. Bayou Texar in Pensacola, FL, receives pollutants from a variety of sources, presumably including two USEPA’s Priorities List sites. To evaluate the potential negative impacts of pollution in this type of setting, we determined the level and distribution of some of the pollutants in the bayou and identified the most likely sources for them. Results show that fluoride, a tracer for a contaminated groundwater plume from one of the Priorities List sites, enters sediments in the northern part of the bayou and migrates into the water. Radium in the bayou most likely also emanates from the contaminated groundwater plume. However, 228 Ra/ 226 Ra isotope ratios indicate that the radium enters the plume from the aquifer matrix, and thus does not originate directly at the Priorities List site. PAHs of creosote origin are known to have been released by the second Priorities List site but apparently they do not affect the sediments of the bayou because ratios of individual PAHs show that they are derived from combustion. The concentrations of the PAHs are slightly higher in the northern part of the bayou. Unlike other pollutants, most metals exceed their probable effects level (PEL) in many places in the bayou. The highest concentrations are observed in the northern part of the bayou. Low metal concentrations in monitoring wells and in deep sediments in the bayou suggest that the metals do not come from the groundwater plume. Sediment transport analysis shows that sediments are trapped in the northern part of the bayou. Consequently, long term accumulation explains the observed high concentrations of heavy metals, and other sediment bound pollutants, in the northern part of Bayou Texar. Pollutant concentrations vary greatly spatially, demonstrating the importance of geographical analysis for this type of environmental research. Keywords: estuary, pollution, heavy metals, PAHs, radium, fluoride, GIS 1. Introduction Two-thirds of the world population lives within 150km of a coast. In the next 25 years the number of people near the coast is expected to double. The environmental impacts of this coastal population are very extensive and have been documented in many locations. Estuaries, especially small urban estuaries, are among the most heavily impacted coastal ecosystems (Lewis et al., 2001b). Water and sediment quality in estuaries have been found to be greatly influenced by urbanization and other human activities (Feng et al., 2004; Ramessur, 2004; Sarkar et al., 2004; Cave et al., 2005). Because of the ever increasing human activities in coastal areas there is a continued need for a better understanding of anthropogenic pollution in Water, Air, and Soil Pollution (2006) 174: 235–263 DOI: 10.1007/s11270-006-9103-4 C  Springer 2006