ALBERT

Description: The fate and cycling of two selected legacy persistent organic pollutants (POPs), PCB 153 and γ-HCH, in the North Sea in the 21st century have been modelled with combined hydrodynamic and fate and transport ocean models (HAMSOM and FANTOM, respectively). To investigate the impact of climate variability on POPs in the North Sea in the 21st century, future scenario model runs for three 10-year periods to the year 2100 using plausible levels of both in situ concentrations and atmospheric, river and open boundary inputs are performed. This slice mode under a moderate scenario (A1B) is sufficient to provide a basis for further analysis. For the HAMSOM and atmospheric forcing, results of the IPCC A1B (SRES) 21st century scenario are utilized, where surface forcing is provided by the REMO downscaling of the ECHAM5 global atmospheric model, and open boundary conditions are provided by the MPIOM global ocean model. Dry gas deposition and volatilization of γ-HCH increase in the future relative to the present by up to 20% (in the spring and summer months for deposition and in summer for volatilization). In the water column, total mass of γ-HCH and PCB 153 remain fairly steady in all three runs. In sediment, γ-HCH increases in the future runs, relative to the present, while PCB 153 in sediment decreases exponentially in all three runs, but even faster in the future, due to the increased number of storms, increased duration of gale wind conditions and increased water and air temperatures, all of which are the result of climate change. Annual net sinks exceed sources at the ends of all periods. Overall, the model results indicate that the climate change scenarios considered here generally have a negligible influence on the simulated fate and transport of the two POPs in the North Sea, although the increased number and magnitude of storms in the 21st century will result in POP resuspension and ensuing revolatilization events. Trends in emissions from primary and secondary sources will remain the key driver of levels of these contaminants over time.

Description: Global climate change has generally increased net primary production which leads to increasing litter inputs. Therefore assessing the impacts of increasing litter inputs on soil nutrients, plant growth and ecological Carbon (C) : nitrogen (N) : phosphorus (P) stoichiometry is critical for an understanding of C, N and P cycling and their feedback processes to climate change. In this study, we added plant litter to the 10–20 cm subsoil layer under a steppe community at rates equivalent to 0, 150, 300, 600 and 1200 g (dry mass) m−2 and measured the resulting C, N and P content of different pools (above and below ground plant biomass, litter, microbial biomass). High litter addition (120% of the annual litter inputs) significantly increased soil inorganic N and available P, aboveground biomass, belowground biomass and litter. Nevertheless small litter additions, which are more realistic compared to the future predictions, had no effect on the variables examined. Our results suggest that while very high litter addition can strongly affect C : N : P stoichiometry, the grassland studied here is quite resilient to more realistic inputs in terms of stoichiometric functioning. This result highlights the complexity of the ecosystem's response to climate change.