The Relationship Between Marsh Surface Topography, Hydroperiod, and Growth of Spartina alterniflora in a Deteriorating Louisiana Salt Marsh

Abstract

The relationships between marsh elevation, flooding frequency and duration, and vegetative growth in a Spartina alterniflora marsh in coastal Louisiana were evaluated using field surveys, tide gauge records, and plant growth measurements over two growing seasons. Hvdroperiod was calculated for different elevations on the marsh surface and relationships determined by regression analysis. Relationships between marsh surface elevation and vegetative parameters changed during the study period. There was a positive relationship between marsh elevation and vegetation vigor. At the beginning of the study, elevation did not appear to influence plant growth, but the effect of elevation on the magnitude of above and below ground standing crop and stem density' increased in the second year. Variations in elevation across the study site (12 cm) cause dramatic changes in hydroperiod (> 200%) for vegetation in different areas. Eh measurements indicate reduced soil conditions associated with long-duration flooding events at lower elevations. These data suggest that more flooded areas of the marsh are deteriorating and we anticipate that plant die-back will occur in this area, resulting in wetland loss