The seasonality of biotic and abiotic processes controls the turnover of organic matter in wetlands

Authors
Chiara Pasut1,2, Fiona H. M. Tang3,6, Budiman Minasny4, Charles R. Warren4, Feike A. Dijkstra4, William J. Riley5, Federico Maggi1,4

1 Environmental Engineering, School of Civil Engineering, The University of Sydney, Bld. J05, 2006 Sydney, NSW, Australia.

2CSIRO Agriculture & Food, Kaurna Country, Gate 4 Waite Road, Urrbrae, SA 5064, Australia.

3 Department of Crop Production Ecology, Swedish University of Agricultural Sciences (SLU), Ulls väg 16, Box 7043, 750 07 Uppsala, Sweden.

4 Sydney Institute of Agriculture, School of Life and Environmental Sciences, The University of Sydney, New South Wales, Australia.

5 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.

6 School of Environmental and Rural Science, University of New England, Armidale, NSW, 2351, Australia

Contact

Chiara Pasut ([e-mail]), 

Background

We described the soil organic carbon cycle SOC using The BAMS4 (Biotic and Abiotic Model for SOM-version 4), which includes five organic C pools: PolyC represents lignin, cellulose, and hemicellulose organic polymers; PolyCN represents peptidoglycan; MonoC, MonoCN, and MonoCS are three low molecular weight organic monomers containing C, C and N, and C and S, respectively, representing monosaccharides, fatty acids, organic acids, phenols, amino acid, amino sugar, and nucleotides resulting from root exudates and depolymerization of PolyC and PolyCN, which contain C, and C and N, respectively. The model included two C pools representing CH4 and CO2. Four microbial functional groups control the SOC cycle: fungi FDEP  are responsible for depolymerisation of PolyC; heterotrophs BAER are responsible for aerobic respiration on MonoC, MonoCN, MonoCS, and PolyCN; methanogens BMGB are responsible for anaerobic respiration on MonoC; and methanotrophs BMOB are responsible for CH4 oxidation. The C cycle was coupled with the N and S cycles to account for the feedback introduced by e- donors and acceptors on the biotic response of each elemental cycle (Figure 1). Specific to the N cycle, we accounted for atmospheric N2 fixation, NH4+ nitrification by ammonia oxidizers BAOB and nitrite oxidizers BNOB, and NO2- and NO3- denitrification mediated by denitrifiers BDEN. For S, we accounted for reduction, disproportionation, and oxidation reactions mediated by sulphur S reducers BSrRB, thiosulfate and sulfite (S2O32-, SO32-) reducers BThSRB, sulfate SO42- reducers BSRB, S2O32- and SO32- disproportioning microbes BSDB, and photolithoautotroph oxidizers BSOB. Each of the organic and inorganic C, N, and S pools can be in the aqueous and gaseous phases, or minerally-associated, that is, protected from biological action. All the biochemical reactions and corresponding parameters are presented in Supplementary Information in Pasut et al., 2021. Table 1 summarizes the pool aggregation used in this work, and each flux from and to each pool.

Contents

We distribute the turnover time and carbon fluxes of global freshwater wetlands. The computational domain covers an average wetland surface area of 3.8 Mkm2 (ranging between 1.2 and 11.4 Mkm2 from 2000 to 2017) described by about 45,000 grid cells at a grid resolution of 0.5 degree (about 50 km at the equator). Grid cells covered by wetlands for at least 2% of the total grid cell area were selected from the SWAMPS v3.2 wetlands database (Poulter et al., 2017), which reported the monthly flooded land area from 2000 to 2017 based on active and passive microwave satellite images excluding lakes, reservoirs, rivers, and saline environments. Each selected grid cell is represented by 2 m atmospheric column that includes four atmospheric layers necessary for heat and gas exchanges, and water flooding (30, 30, 40, and 100 cm thick from land surface upward), one layer of the topsoil (0 to 30 cm), two layers of subsoil (30 to 100 cm), and one layer below the root zone (100 cm thick). Each grid cell is characterized by a depth-specific soil bulk density, porosity, and textural soil fractions (Poggio et al., 2021), hydraulic and thermal conductivity, heat capacity, air-entry potential, and pore volume distribution index (Dai et al., 2013). Table 1 summarizes the data released in this version and the corresponding variables.

Resources

BAMS4 was integrated in a general-purpose multiphase and multi-species bioreactive transport simulator, BRTSim-v5.0b solver. The BRTSim-v5.0b solver package can be downloaded at https://sites.google.com/site/thebrtsimproject/home or from the mirror https://www.dropbox.com/sh/wrfspx9f1dvuspr/AAD5iA9PsteX3ygAJxQDxAy9a?dl=0.

Georeferencing system

Resolution: 0.5°×0.5° (approximately 55 km at the equator)

Pixel resolution: 360 by 720

Coordinates: standard WGS84

Bounding box: 180°E-180°W; 90°S-90°N