Semester of Graduation

Summer 2022


Master of Oceanography and Coastal Sciences (SOCS)


Oceanography and Coastal Sciences

Document Type



Phragmites australis (Cal.) Trin. Ex Steud, or common reed, is a cosmopolitan emergent macrophyte with many distinct haplotypes, or individuals of a species that share an inherited group of genes or alleles. In 2016, widespread die-back occurred in the lower Mississippi River Delta (MRD), Louisiana. In a delta-wide field survey and a mesocosm study, we investigate if haplotypes vary in environmental niches and respond differently to potential abiotic stressors (marsh elevation & flooding frequency, nutrient loads, sulfides, & Fe2+) of the three common haplotypes of P. australis in the MRD: Delta (haplotype M1), Gulf (haplotype I), and EU (haplotype M). Haplotypes differed significantly in their elevation, substrate conditions, morphologies, and morphological responses to environmental conditions. Delta, the predominate haplotype affected by die-back, occupies substrates lower in soil bulk density with higher percent organic matter, increased porewater concentration of sulfides, and lower elevation with increased periods of flooding from 2014 – 2021. In the mesocosm experiment, haplotypes were subjected to varying period of flooding above soil surface (0%, 50%, 100%), along with differing water types (tap & MRD) containing varying levels of nutrient concentrations. Important morphological differences were found among three Phragmites haplotypes in both above-and belowground growth patterns. Aboveground biomass growth (ABG) was affected by flooding frequency in EU as significantly less ABG was produced at high elevation than the medium elevation. Gulf produced significantly less root and rhizome biomass in the low elevation treatment, while Delta produced more root biomass in the high elevation treatment. The interaction between water treatment and elevation produced taller stem heights in the low elevation treatment across haplotypes.



Committee Chair

Tracy Quirk

Available for download on Monday, July 09, 2029