Lee, H., R. Diaz and J. T. Cronin. In review. Phragmites australis dieback in the Mississippi River Delta: chemical profiles of healthy, dieback and dredge soils and impacts on plant biomass. For Estuaries and Coasts.


Causes of extensive dieback of Phragmites australis in the Lower Mississippi River Delta (MRD) are poorly understood. We characterized the chemical profiles of soils collected from healthy and dieback stands of P. australis, and from sites recently created from dredge-disposal soils that were expected to be colonized by P. australis. Chemical properties included Al, Ca, Cu, Fe, K, Mg, Mn, Na, P, S, Zn, % organic matter, % carbon, % nitrogen, and pH. To assess restoration potential in dieback and dredge sites, we experimentally tested whether these different soil types impact P. australis growth (stem height, stem number, and biomass). In each soil type, we planted rhizomes of the three common P. australis lineages, Delta, Gulf and European, and measured plant growth after five months. Dieback soils were characterized by higher % organic matter, % carbon, % nitrogen, and higher S and Fe concentrations, whereas healthy soils had higher Cu, Al, P and Zn. In comparison, dredge sites were low in nutrients and organic matter compared to healthy soils. Aboveground biomass was 16-23% lower in dieback and 44% lower in dredge soils than in healthy soils. Dieback soils most negatively affected Delta followed by European and Gulf lineages. Although dredge and dieback sites are not optimal for P. australis growth, plants can thrive on these soils, and we recommend restorative measures be initiated as soon as possible to minimize soil erosion.