|
|
|
Graduate Research Fellows Library
|
|
 |
Reconstruction of vegetation history and accretion rates in coastal marshes: Understanding past responses to sea-level rise at Grand Bay
Rebecca Cripps
Coastal wetlands are stressed by natural and anthropogenic impacts that may influence processes contributing to maintenance of marsh surface elevations relative to sea level. To predict coastal marsh response to future sea-level rise, it is important to understand how marshes responded to past sea-level rise. The objective of this study was to reconstruct vegetation history and accretion rates from sediment cores collected in Grand Bay National Estuarine Research Reserve (NERR), Mississippi, USA. Vegetative fragments preserved in cores were identified using a dichotomous key based on characteristics of modern plant species common in coastal marshes of the northern Gulf of Mexico. Soil characteristics (e.g., bulk density, organic matter content), accretion rates from 137Cs activity, and radiocarbon dates were also determined. The initiation of Cs-137 occurred at a depth of 41 cm, indicating an accumulation of 41 cm of sediment since 1954 (accretion rate = ~0.745 cm/yr). However, this rate appears to have slowed since 1963 when Cs-137 peaked at a depth of 14 cm (accretion rate = ~ 0.304 cm/yr). Vegetation and soil characteristic data were processed through a program called SiZer to determine significant shifts or changes of vegetative community and soil characteristics over time. Four significant shifts in the vegetative community and two main shifts in bulk density were detected. From these results, Grand Bay marsh appears to have maintained its surface elevation relative to sea-level rise through both physical and biological processes where long periods of organic matter accumulation (demonstrated by presence of preserved vegetation) are interspersed with periods/pulses of sediment deposition (demonstrated by increases in bulk density) over time.
|
|
