Title: Developing a Reliable Method for Identifying Pre-settlement Wetland Sediment Accumulation Rates: 14C Dating on Bulk Lake Sediments and Extracts
Project Type: Information Transfer
Start Date: 03/01/2006
End Date: 02/28/2007
Congressional District: 1st
Focus Categories: Wetlands, Sediments, Methods
Keywords: Wetlands, Sedimentation, 14C
Principal Investigator: Davidson, Gregg R.
Federal Funds: $14,890
Non-Federal Matching Funds: $30,381
Mississippi Water Research Priorities addressed:
Wetlands and Sedimentation Sediment accumulation rates in lakes and wetlands are known to increase when neighboring land is converted to agricultural use, but the magnitude of historical changes is often difficult to assess. In most areas, few records exist on the natural rate before large-scale changes in land use began. This is particularly true in areas such as the heavily cultivated Delta region of Mississippi where most of the land was cleared more than a century ago. Standard methods such as 137-Cs and 210-Pb dating techniques are useful for establishing modern sediment accumulation rates in these areas, but not for establishing rates prior to settlement.
When land managers are tasked with implementing measures to reduce sediment accumulation rates in wetlands and lakes, it is critical that they have an understanding of what the rates of accumulation were naturally. Carbon-14 has often been used in lake studies to determine the age of specific layers or to determine ancient sedimentation rates, but methods generally rely on identifying recognizable plant fragments or fossils that are often difficult to find. Where visible, identifiable specimens are lacking, pollen samples may also be extracted and dated, but this is a tedious and time consuming task. Preliminary data from an oxbow lake-wetland in Mississippi suggests that a simplified approach utilizing extracts from bulk sediment samples or low temperature combustions of clays may yield reliable pre-settlement sedimentation rates.
Statement of the results, benefits, and information gained:
The result of this work is expected to yield an improved and simplified 14C-method for establishing natural sediment accumulation rates in lakes and wetlands that pre-date large-scale changes in surrounding land use. When addressing the need to reduce sediment flux to acquatic systems, it is imperative to first understand what the natural flux was before adjacent lands were cleared and tilled. Preliminary data already collected suggests that the proposed technique will prove useful as a practical method for establishing natural background sedimentation rates.
The research will also facilitate collaboration between the University of Mississippi, the Yazoo Mississippi Delta Joint Water Management District (TMD), the USDA National Sedimentation Laboratory, and the Unviersity of Arizona. Only YMD is listed in the budget because they are the only non-federal, in-state collaborator on this project, and no funds are required from the other agencies to complete the proposed project. Letter of support are attached to the end of the proposal. (The letter from the University of Arizona notes that additional funding to offset the cost of analyses is desirable, but is not required for the successful completion of this project.
Progress/Completion Report, PDF