Thresholds of Change in Decomposition Rate along a Dune/Swale Transect on a Virginia Barrier Island

Abstract

Graziani, D.J. and Day, F.P., 2015. Thresholds of change in decomposition rate along a dune/swale transect on a Virginia barrier island. Journal of Coastal Research, 31(1), 148-154. Coconut Creek (Florida), ISSN 0749-0208.The objective of the current study was to examine fine spatial scale variation in aboveground decomposition rate over a barrier island dune/swale gradient in relation to the ground-water-free surface, soil nitrogen, and associated ecosystem states in order to identify thresholds of process or state change. The litterbag study was conducted on the Virginia Coast Reserve-Long Term Ecological Research Site in Virginia, United States. Mean aboveground decay rate (yr À1 ) ranged from 0.339 (upper dune) to 0.699 (marsh/lower dune transition). The upper dune, marsh, and lower dune (Morella thicket side) had the lowest aboveground decay rates. The marsh edge, marsh/lower dune transition and Morella thicket exhibited the highest decomposition rates. Our results did not suggest that soil N content was a good indicator of state change or system process rates, whereas, distance to ground water demonstrated a significant relationship with aboveground decay. Relatively small (approximately 0.2-0.4 m) increases or decreases in elevation affected decay rates and community state. Free-surface thresholds that cause state changes or shifts in ecosystem processes provide the capability to project changes prompted by sea-level rise or shifts in other free surfaces over entire landscapes. Our results suggest that the ground-water-free surface is a good candidate for making such projections.

Legacy effects of altered flooding regimes on decomposition in a boreal floodplain

“…In line with our hypothesis and existing literature we found that stabilization of the labile fraction (S) was highest at high elevation and decomposition of local litter was stimulated at low incubation elevation (Graziani and Day 2015;Hefting et al 2005;Xiong and Nilsson 1997). In contrast with our hypothesis, however, we found the lowest TBI decomposition rate (k) at low incubation elevation.…”

“…Letters behind the means indicate significant differences between local litter types, based on a One-way ANOVA and a Tukey post-hoc test legacy effects of flooding (e.g., deposited sediment, soil moisture, vegetation die-back), because the litter bags themselves were not exposed to a flooding event. Soil moisture and soil temperature were higher at low incubation elevation, and this can enhance decomposer activity and hence litter breakdown there (Berg et al 1993;Graziani and Day 2015). In line with our tea bag experiment, and despite differences in setup, the local litter incubations show that the incubation elevation strongly affects plant litter breakdown, indicating that changes in flooding regimes will have an immediate impact on decomposition processes.…”

Immediate effects of microclimate modification enhance native shrub encroachment

“…The amount of organic matter inside the thicket was smaller than that found in older thickets (Crawford and Young ). More time may be needed to decompose litter (Graziani and Day ). Higher soil N was caused by the nitrogen‐fixing effects of Frankia , the symbiotic bacteria living in root nodules of M. cerifera (Young et al.…”