Saltmarshes are highly dynamic ecosystems influenced to a large extend by human impact and sea level rise. Since tidal marshes sequester large amounts of carbon and represent a potential source of various greenhouse gases, it is important how shifts in environmental factors (e.g. sea level, oxic conditions) affect biodiversity and ecosystem functions (e.g. nutrient cycling and decomposition) in these areas. In order to understand the biodiversity traits and their temporal dynamics, a unique field experiment consisting of six vegetated experimental islands (EI) in the Wadden Sea of Germany was conducted. The islands consist of three elevations according to the three major saltmarsh zones of pioneer zone (PIO), lower saltmarsh (LOW) and upper saltmarsh (UPP). Sods from the natural habitat of LOW were transplanted onto the islands into all three elevation steps to manipulate biodiversity. Same actions were performed in the saltmarsh ecosystem as a control (SMC). After one year, Carbon and Nitrogen were measured to test for shifts towards marine or terrestrial environmental patterns. Furthermore, a Tea-bag experiment (TBI) was carried out on all plots to highlight differences in decomposition of plant material depending on environmental conditions.
Results/Conclusions
During one year, both soils from EI and SMC increased in C and N. EI enriched 12.9% more C than SMC during winter at all elevations (+15.8% N). Regarding C/N-Ratio, PIO decreased by one on EI and SMC. In UPP-plots, ratio increased by one on SMC, whereas no difference on EI occurred. The higher preservation and accumulation of organic matter due to plant die off on EI compared to SMC after winter indicate harsher impact of abiotic factors (e.g. drought- and temperature stress) on EI. Decrease of C/N-Ratio in PIO shows a shift towards a marine environment because algae have lower C/N-Ratios compared to vascular plants (vice versa in UPP). However, no shift in UPP on EI means limitation of seed dispersal onto EI from mainland. TBI showed low decomposition rates k (max. 0.01) and medium stabilization factors S (0.2-0.45) comparing to other ecosystems. Decomposition rate increased with elevation gradient. Reasons are a hampered decomposition in PIO due to salt- and oxygen-stress, whereas in UPP a competition dominated environment with a high demand for N is apparent. In conclusion, established EI represent good testing sites for simulated sea-level rise and its effect on fast adapting saltmarsh communities.