1. TRACE METAL AND DIOXIN DEPOSITION HISTORY IN HURRICANE KATRINA IMPACTED MARSH SEDIMENT Gopal Bera* and Alan Shiller (The University of Southern Mississippi, Stennis Space Center, MS, USA) Kevin M. Yeager (The University of Kentucky, Lexington, KY, USA) INTRODUCTION STUDY AREA SLB_2 SLB_1 RESULTS AND DISCUSSION SLB_3 SLB_4 Acknowledgement: This project is funded by Mississippi DMR through CIAP. TiO 2 refinery began operation in 1979. Event layer 1979 1979 ? 1979 Event layer TiO 2 Refinery St. Louis Bay Jourdan River Wolf River Outfall Cs concentration has increased 5-8 fold in SLB marsh over the last ~30 years. Impacts of Hurricane Katrina on pollution history are not pronounced in these cores. Reasons could be: 1) source material originated from SLB or from marsh itself and thus has same chemical content. 2) need high resolution (every 0.5 or 1 cm instead every 5 cm) metal profiles. 3) Hurricane Katrina layer has been destroyed by extensive bioturbation. Preservation potential of hurricane event layer in SLB_2 is highest among the four cores. CONCLUSIONS Salt marsh sediments have been used in pollution chronology studies because of their: 1) clay-rich nature and high contaminant adsorption capacity (Valette-silver, 1993), 2) often steady and high sedimentation rates (Yeager et al., 2012; Stumpf, 1983), and c) dense, stabilizing root systems (Cundy et al., 2003). However, major hurricanes can modify coastal landscapes by eroding and re-distributing sediments via waves and storm surge (Turner et al., 2006). The physical characteristics and chemistry of hurricane event layers can be much different than the organic-rich marsh sediment they replace and/or bury (Reese et al., 2008; Nyman et al., 1996). Thus, deposition of hurricane event layers in marshes can significantly impact the depositional record of contaminants derived from atmospheric and/or fluvial sources. Generally, preservation of hurricane event layers depends on: a) rate and thickness of sediment mixing (bioturbation, physical), b) rate of sedimentation, c) thickness of event layer, and d) sediment sources (Wheatcroft and Drake, 2003). These factors can vary significantly with marsh zonation (Reese et al., 2008). We have examined pollutant chronology in marsh sediments of St. Louis Bay, MS, an area that was directly impacted by Hurricane Katrina in 2005. Among the anthropogenic sources of pollutants to this bay is a TiO 2 production facility in the northern part of the bay which appears to be a source of various metals and dioxins. High sedimentation rate, a thin mixed layer, a thick hurricane event layer, and low bioturbation rates favor the preservation of hurricane event layers. Assuming the same thickness of hurricane event layer for all four cores, mixing depth and bioturbation rate determine the preservation potential of event layer in these cores. SLB_1 has thickest mixed layer and its bioturbation rate is likely very high. But, SLB_1 also has sediment with abundant sand (~upper 25 cm) which may inhibit bioturbation. SLB_4 has lowest elevation, and in low marsh, fiddler crab activity can be extensive and preservation potential of a hurricane event layer may be poor. SLB_2 and SLB_3 are 300-400 meter landward from bank and have intermediate bioturbation rates. Thus, these cores have high potential to preserve a hurricane event layer. Note: Sedimentation rates are calculated from Cs profile. As the Cs was determined only every 5 cm, calculated sedimentation rates or assigned date (1979) have significant uncertainty. TiO 2 refinery is the likely source of Cs (used in refining process) to the bay and surrounding areas. Dioxin data from EPA, SLB_6 and SLB_7 are still being processed. St. Louis Bay sediment has a history of Cr, Ni and dioxin contamination. Elston et al. (2005) found significant increases in these contaminants compared to a baseline study (Lytle and Lytle, 1978). The TiO 2 refinery was thought to be prime source for these contaminants. Metal profiles show increasing trends of V and Cr in all cores except SLB_3, which is located the farthest away from the outfall of the TiO 2 refinery. The Cs concentration increased from background levels (3-5 µg/g) to 20-24 µg/g after the TiO 2 refinery started operation. Again, this increase is not pronounced in SLB_3. The impact of Hurricane Katrina on the pollution history recorded in these sediments is not pronounced. Appropriate identification of hurricane event layers and high resolution metal profiles are needed (and will be adopted) to clearly identify the impact of large hurricanes on pollution history.