Focus

Species composition, seasonality and productivity of fen vegetation exposed erratically to brackish water intrusion will be compared with neighbouring fens fed by freshwater only. The main focus is to unravel the impact of temporal salt water on vegetation communities and matter cycles.

State of the art

Fen vegetation is already specialised to a stressful environment requiring adaptation to an organic-rich, hypoxic soil. Putting salinity as an additional stressor may impact composition or at least productivity. For tidal swamps and fens salinity has been demonstrated to be a main factor, shaping species composition and productivity in a characteristic manner and resulting in marsh wetlands. However, for atidal areas no such data exist and therefore investigating vegetation composition, productivity of the habitat-forming species and decomposition of plant litter in temporarily salt-impacted fens in comparison with freshwater fens of similar nutrient and climatic conditions is needed to estimate the effects of altered coastal defence regimes.

Work program

Species composition, coverage and recruitement potential of fen vegetation exposed to intermittent salinity impact will be compared with data taken from pure freshwater-fed fens. Causal analysis of differences found will be performed by means of laboratory-based acclimation experiments, respecting for on-site pre-adaptation. These investigations will prepare for studying habitat filtering effects, shaping the genetic structure of brackish communities.In parallel, impact of salinity shifts on decomposition characteristics of plant litter material and, consequently nutrient cycles, will be studied.