Relationship of Marsh Elevation, Redox Potential, and Sulfide to Spartina alterniflora Productivity

Abstract

AbstractData presented suggests that the short height form of Spartina alterniflora observed in inland areas of Louisiana Gulf Coast marshes is caused by toxic concentrations of sulfide, a result of slightly lower elevation and subsequently lower sediment redox potential than the adjacent productive streamside marsh. It is speculated that sulfide may limit growth by preventing nitrogen uptake and root development. Total sulfide concentrations as high as 250 µg g−1 of sediment and free sulfide concentrations in the order of 150 µg g−1 were found in the inland sediment. The inland sediment contained higher NH+4‐N concentrations at depth than the streamside sediment. The higher NH+4‐N concentrations closely paralleled the increasing sulfide concentrations and was inversely related to rooting depth. Maximum NH+4‐N concentrations of 60 and 16 µg N g−1 of dry soil was observed in the inland and streamside sediment, respectively. Redox potential was higher at the surface sediment of the more productive streamside marsh compared to the adjoining inland marsh. The higher redox potential is mainly due to the higher elevation of the streamside area that permitted greater drainage. This in turn allowed the development of more oxidized sediment containing lower sulfide levels. Observed differences in salinity and plant‐dissolved nutrients were not great enough to restrict plant growth.