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Alternate Title

The Effects of Flooding on Four Common Louisiana Marsh Plants

Abstract

The marshes of the Louisiana coastline have been deteriorating for decades as plants experience increasing levels of flooding. In this study, we determined the effects of flood duration on four of the most common marsh plants in Louisiana—Spartina alterniflora, Spartina patens, Panicum hemitomon, and Sagittaria lancifolia—by exposing them to different flooding regimes: 0%, 20%, 40%, 60%, 80%, and 100% of the time flooded. Cumulative plant height, soil redox, and soil pH were measured weekly. At the end of the experiment, above- and belowground biomass were measured. Redox measurements showed that the saturated soil (0% flooded) was slightly depleted of oxygen at a redox potential of 300 mV, whereas oxygen was depleted and nitrate and/or manganese used as electron acceptors in all the flooded treatments (20–100% flooded), which had an average soil redox potential near 200 mV. In the saturated treatment, the soil was slightly acidic (pH average 4.7), whereas the flooded treatments had neutral soil acidity (pH average 7.3). Spartina alterniflora biomass was significantly affected by flooding. Spartina alterniflora biomass in the saturated treatment was approximately twice the biomass achieved in any of the flooding treatments. Spartina patens showed a rapid decline in biomass with increased flood duration, reaching the lowest values in treatments that were flooded more than 50% of the time. Although aboveground biomass of Sagittaria lancifolia was not significantly related to flooding regime, belowground biomass decreased with increased flooding duration. The only species that showed no significant response to flooding duration was P. hemitomon. Our results suggest that wetland restoration techniques that reduce flooding frequency are most appropriate for organic marshes dominated by Spartina patens and Spartina alterniflora, whereas these techniques may be less appropriate for organic marshes dominated by Sagittaria lancifolia and P. hemitomon.

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