| Summary |
Many coastal ecosystems migrate landward under the influence of rising sea level. Typical zonation of plant communities along coastal shorelines consists of tidal marshes, a transition zone, and adjacent upland or wetland forest. This study examined organic matter distribution along this gradient. I hypothesized that total above and belowground organic carbon mass would follow the pattern: forest > transition > high marsh = mid marsh > low marsh > tidal creek. This study was conducted at the upper Phillips Creek study area on the eastern shore of Virginia. A zonation map of the study area was created, and low marsh was divided into two zones based on two growth forms of Spartina altemiflora. Sample sites were selected using a stratified random sampling approach. A nested plot design was used to harvest vegetation, obtain soil cores, and collect quantitative data on trees, shrubs and large wood detritus. Unharvested tree and shrub masses were estimated using regression equations. Loss on ignition was determined for vegetation and soils. Organic carbon mass was estimated to be 50% of organic matter. Total above and belowground organic carbon mass (mean kg/m² [plus-or-minus] S.E.) for each zone was; forest 24.3 [plus-or-minus] 2.1, high marsh 14.2 [plus-or-minus] 0.7, transition 12.8 [plus-or-minus] 0.6, low marsh short-form Spartina altemiflora 12.6 [plus-or-minus] 0.8, low marsh tail-form Spartina altemiflora 11.3 [plus-or-minus] 0.7, and tidal creek 8.7 [plus-or-minus] 0.3. The greatest loss of carbon occurred in the transformation of forest to high marsh. Organic carbon turnover rates were estimated for steep and gentle slopes by projecting an 80-year period of sea level rise at 5 mm/year. After 80 years, marsh and transition zones experienced 100% turnover in both profiles. The forest experienced turnover rates of 25% and 71% in steep and gentle profiles, respectively. Horizontal turnover rates of carbon associated with state change were approximately one order of magnitude lower than those associated with net primary production. However, horizontal turnover of ecosystem states can change coastal landscapes within the time span of a century. |
