Carbon Dioxide Fluxes and Plants Interactions across the Succession of a Created Brackish Marsh in Southwestern Louisiana

The purpose of this study was to examine: 1) carbon dioxide (CO2) fluxes in different plant communities in a created and natural brackish marsh and 2) the role of an early colonizing species, Spartina alterniflora, in facilitating or suppressing a later colonizer and higher marsh species, Spartina patens. CO2 fluxes were measured in four key successional stages: 1) non-vegetated sediment of a newly created marsh; 2) Spartina alterniflora-dominated areas of a newly created marsh; 3) S. alterniflora-dominated natural marsh; and 4) Spartina patens- dominated natural marsh. Spartina alterniflora-dominated areas were sinks for CO2 in both created and natural marsh with an average CO2 uptake rate of 7.0 (± 1.0) μmol m-2s-1. Bare sediment in the created marsh and S. patens in the natural marsh had approximately net neutral CO2 fluxes with bare sediment averaging 0.2 (± 1.0) μmol m-2s-1 of CO2 efflux and S. patens areas averaging 0.2 (± 1.0) μmol m-2s-1 of CO2 uptake. CO2 fluxes were found to be mainly determined by plant community type and significantly related to aboveground biomass. Because vegetation develops much faster than soil properties in created marshes, these findings indicate that CO2 fluxes can reach similar levels to that of natural marshes relatively quickly following marsh creation. To determine S. alterniflora interactions with S. patens in developing created marshes, S. patens were transplanted into either bare sediment or within S. alterniflora clones. Spartina patens transplanted into the bare sediment expanded at a rate of 33.0 (± 9.0) cm-2month-1, and had a stem density of 2115 (±180) stems m-2. Spartina patens transplanted within S. alterniflora contracted in area at a rate of -3.0 (± 3.0) cm-2month-1, and had a stem density of 1362.5 (±164) stems m-2. These results indicate that S. alterniflora presence impedes S. patens establishment in a created marsh. The created marsh was found to have a large reserve of available nitrogen in the bare sediment possibly favoring S. alterniflora. Together these studies illustrate that created marsh plant community development is important for CO2 fluxes but plant iterations may differ in a young created marsh from a natural marsh.