Soil Properties and Geochronology in Barataria Basin, Louisiana

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Will wetland vertical accretion rates be enough to keep up with the predicted rates of sea level rise? USGS looks at soil properties and geochronology in Louisiana wetlands. 

Marsh core, Barataria Basin, Louisiana
Marsh core, Barataria Basin, Louisiana

Science Issue and Relevance: The wetlands of the Mississippi River delta have undergone tremendous loss over the past century, a fate shared by many river deltas globally. Though several mechanisms such as insufficient sediment supply and saltwater intrusion have been linked to the delta’s deterioration, excessive submergence has been linked to over 50% of this wetland loss since 1932. Thus, it is important to assess whether wetland vertical accretion rates are sufficient to keep pace with predicted rates of sea-level rise and to identify the processes that drive this vertical accretion and how the relative importance of these processes varies through space and time. A key component of efforts to restore these wetlands entails using Mississippi River diversions to increase mineral sediment supply as a means to stimulate inorganic sediment accretion. Marsh flooding induced by diversions may diminish plant productivity and ultimately reduce organic matter accumulation. In addition to providing a baseline data source by which to assess the impact of proposed river diversions on wetland soils, this study aims to quantify vertical accretion rates throughout the Barataria basin and determine the relative importance of organic and inorganic matter accumulation in driving vertical accretion.

Soil properties data, Barataria Basin, Louisiana
Soil properties data, Barataria Basin, Louisiana 

Methodology for Addressing the Issue: A total of 25 marsh cores will be collected across Barataria Basin in February and March of 2016. Cores will be collected with 10-cm diameter, thin-walled aluminum pipes 60 cm in length. Cores will be sliced into 2-cm thick sections, and each section assessed for 210Pb and 137Cs activity, bulk density, loss-on-ignition (LOI), and total carbon. Activity profiles of 210Pb and 137Cs will be used to derive vertical accretion rates; accretion rates, bulk density, and LOI data will be used to calculate rates of organic and inorganic matter accumulation. Profiles of mineral and organic contributions to soil volume as a function of depth will be constructed, and rates of organic and inorganic accumulation will be interpolated across the basin as a first step toward developing a sediment budget.

Future Steps: The soil properties data obtained in this effort will be used to determine long-term rates of carbon sequestration across the wetlands of the Mississippi River delta plain.

Location of the Study: Throughout the Louisiana coastal zone, Latitude: 29.678°, Longitude: -91.552°