Vertical Record of Ecological Change and Carbon Storage in a Young Emergent Mississippi River Coastal Deltaic Floodplain
Abstract
Coastal deltaic floodplains are responsible for 40-50% of global coastal and marine carbon (C) burial and yet are often excluded from blue carbon literature. The Wax Lake Delta (WLD) is an unplanned Atchafalaya bayhead delta formation resulting from the dredging of the Wax Lake Outlet in 1942 to reduce downstream flooding of Morgan City. Twelve 4-5 m Vibracores were taken throughout the delta chronosequence to investigate ecological succession and C storage during the entirety of WLD's development. An oyster shell bed that can be found throughout the delta delineates the beginning of the WLD facies in 1952. As a young active delta its sediments are dominated by fine sand. However, the upper 0.4-0.7 m demonstrate a distinct transition to increased organic matter (OM) inputs, and in the upper half of this layer >90% of the C is organic. Spikes in organic matter and C content correspond to decreases in bulk density through the record. Notably, at 2.5 m depth there is a low bulk density layer corresponding to an increase in organic matter and C that is found throughout the older subaerial delta. This layer formed in 1970, a few years before WLD became subaerial in 1973 and therefore likely represents the point at which vegetation colonization began. Atomic N:P ratios, which are ecological indicators of biological influence, also demonstrate trends similar to OM and C further supporting this interpretation. With over 40 years of continuous subaerial land building, WLD provides a stark contrast to most of Louisiana's retrograding coastline and is considered a model for future sediment diversions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFMOS33A1447A
- Keywords:
-
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0497 Wetlands;
- BIOGEOSCIENCES;
- 4805 Biogeochemical cycles;
- processes;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL;
- 4806 Carbon cycling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL