An Assessment of Metal Profiles in Sediments from Mississippi River Estuaries and Offshore Shoaling Regions

Abstract

Sediment contamination poses a significant problem within aquatic systems. Metals as a pollutant are a major concern because of their toxicity, persistence and non-degradable nature. This study measured sediment metal concentrations within Louisiana’s coastal estuaries and offshore shoaling regions over a three year period. This was done to determine current concentrations, examine the relationships of physico-chemical, spatial and temporal variables with the metals and compare the metal concentrations to established Sediment Quality Values (SQVs). Variables and physico-chemical parameters were run in a comprehensive statistical model to determine variable contribution to the variation of each metal concentration. Moisture content and organic matter were the two physico-chemical variables that were significant among most of the metals within the study. Spatial variables were also found to be significant, with inshore transects having higher concentrations for most metals with the exception of Cd, which was higher offshore. More specifically the highest concentrations occurred at the Atchafalaya and Breton Sound transects for most metals. There were two temporal variables, year and season. Concentrations decreased for five metals and increased for three over the three year period of this study. Both the summer and fall seasons had higher concentrations than the spring season within the season variable. Lastly, metal concentrations between locations that were oiled and those that were non-oiled during the Deepwater Horizon oil spill were compared. Cobalt had statistically higher concentrations at locations allocated oiled, while Cu had higher concentrations at locations labeled non-oiled. Most metal concentrations in this study were below their respective SQVs, which are used by federal agencies to screen sediments for toxicity. xii Knowing the influence environmental, spatial and temporal variables have on metal concentrations is useful in the assessment of sediment quality – specifically when environmental disasters, such as hurricanes or oil spills, repeatedly occur. Determining if the levels of metals have toxic effects on aquatic systems, organisms and humans is a critical first step. This study, the first comprehensive assessment of metals in Mississippi River estuarine sediments, has contributed to developing effective management strategies to control sediment pollution in coastal Louisiana and deltaic systems worldwide.