Showing papers by "Denise J. Reed published in 1992"

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

Effect of weirs on sediment deposition in Louisiana coastal marshes

Abstract: Sediment deposition both inside and outside of fixed-crest weirs was measured for fresh/intermediate, brackish, and saline marsh areas in coastal Louisiana, USA. Sediment traps, collected on a weekly basis, were used to monitor short-term changes in sediment deposition. Feldspar marker horizons were used to measure cumulative marsh accretion during the 16-week monitoring period. Results show that for most sites less sediment is deposited in marsh behind weirs than at the control sites outside the weirs. Patterns at each site are consistent throughout the 16 monitoring periods. At only one site was no significant difference found. Streamside areas both inside and outside the weirs were found to have higher rates of sediment deposition than backmarsh areas. At both marsh locations, sediment deposition rates were higher outside the weirs than inside. More sediment was deposited in saline marshes than in brackish or fresh/intermediate areas. The vertical accretion data shows that marshes in most areas are accreting sufficiently rapidly to keep pace with local rates of sea-level rise, except for two areas, both of which are inside weirs.