Assessment of the 137Cs Method for Estimating Sediment Accumulation Rates: Louisiana Salt Marshes
Keywords:Core quality, sediment accretion, Cs inventory, methodology, sediment dating
Sediment cores were collected at 33 salt marsh locations in the Louisiana Deltaic Plain and subjectively classified as impaired or healthy using aerial imagery obtained since the 1950's. Cesium-137 inventories from these cores were compared with aerial deposition records of nuclear fallout from the southern United States. A system for assessing quality of the 137Cs data was used on these cores. Some cores were found to have deficits in 137Cs inventory, while others had excesses. Therefore, wash-in from outside the basin and erosional loss of 137Cs could be a problem in some of these marshes. Several of these cores had significant amounts of 137Cs in the surface layers, whereas aerial deposition of 137Cs has been virtually zero since 1982. This pattern may result from recent redistribution of sediments with 137Cs being deposited onto the top layer (in which case there should be a zero-activity layer in between), or removal of surficial sediments in the last 8 years. Salt marshes with active depositional or erosional surfaces may not reflect the aerial deposition of 137Cs therefore cores from those markers should be interpreted with caution.