Carbon-Nitrogen-Sulfur dynamics in global wetlands

Wetland ecosystems control the global greenhouse gas emissions. However, almost 22% of the global wetlands are affected by excess nutrients runoff from surrounding agriculture (Figure 1), which may critically modify the pre-existing biogeochemical dynamics.

We studied how the soil organic matter is linked to the nitrogen and sulfur cycles using BRTSim coupled with the BAMS4 model of the C-N-S cycles in wetlands at a global scale (0.5°x0.5° resolution). The coupled BRTSim-BAMS4 biogeochemical model was also coupled with a precipitation-runoff model to account for the nutrients loads resulting from agricultural fertilization runoff during the period from 2000 to 2017. The modelling shows how the greenhouse gasses emissions (CH4 and N2O) and the nutrient sequestration rates are distributed globally and where specific hotspots are distributed (animation in Figure 3 and 4). Additionally, the model describes the biomass dynamic of each biogeochemical reaction, hence we were able to model the hysteretic relationship with CH4 emissions and temperature, and also capture the second peak of emissions in Autumn, while N2O emissions are mostly linked to fertilization rates (Figure 2).

Figure 1. Global wetland and agricultural area distribution.

Figure 2. Dynamic analysis: CH4 with changing temperature (a), SOM input (b), and BMGB concentration (c) during one year (long term average for each Koppen-Geiger classification); N2O with changing temperature (g), SOM input (h), and BDEN concentration (i) during one year (long term average for each Koppen-Geiger classification). January is represented as a dot and the direction of the arrow represents the following months.

Figure 3. CH4 emissions.

Figure 4. N2O emissions.