Showing papers by "Denise J. Reed published in 1989"

Patterns of sediment deposition in subsiding coastal salt marshes, Terrebonne Bay, Louisiana: The role of winter storms

Abstract: High rates of wetland loss in the Mississippi deltaic plain have been attributed to a combination of insufficient marsh sedimentation and relative sea-level rise rates of over 1.2 cm yr−1. This study examines contemporary patterns of sediment delivery to the marsh surface by evaluating the contribution of individual marsh flooding events. Strong meteorological effects on water level in Terrebonne Bay often mask the usual microtidal fluctuations in water level and cause flood events to be of unpredictable frequency and duration. Sediment deposited on the marsh surface was collected weekly at two sites. Preliminary results allow the relative contributions of tidal and storm inundations to be calculated. Maximum sedimentation is associated with strong southerly winds both causing increased flooding and mobilizing sediment from open bay areas. Sediment deposition is limited by the availability of suspended sediment and the opportunity for its transport onto the marsh surface.

Understanding salt-marsh accretion, Scolt Head Island, Norfolk, England

Abstract: Measurements of surface sediment accretion have been obtained for Hut Marsh, Scolt Head Island, Norfolk, England, using sand marker horizons. More than eighty 1-m2 marker sites were deployed in October 1983, and vertical accretion measured at them in April and October 1986 and April 1987. Elevations relative to Ordnance Datum were established by levelling each site at the time of deployment. Data collected by Steers between 1935 and 1957 on the same marsh show a clear relationship between marsh elevation and sedimentation. The results of the current more detailed study, presented as mean annual accretion rates, indicate a complex pattern of sediment distribution at this macrotidal location. These data, together with the results of tidal flow monitoring in the creeks on Hut Marsh, show the importance of spatial and temporal patterns of sediment delivery and variations in depositional processes in determining the distribution of sedimentation across the marsh surface.

Environments of Tidal Marsh Deposition in Laguna San Rafael Area, Southern Chile

Abstract: Surveys of tidal marshes associated with environments of glacial retreat, braided river channel migration, and earthquake-induced subsidence revealed variations in marsh topography and morphology. Profiles show changes in marsh elevation caused by variations in substrate conditions and depth. Types of marsh surface pan, characterized by the absence of vegetation and the retention of water at low tide, are found in all three marsh environments. Classic channel pans are found, as well as other pan morphologies related to local surface conditions. Pans may be either primary or secondary marsh surface features, but are found in all three types of marsh.