Existing soil carbon models do not apply to forested wetlands

Abstract

When assessing the biological, geological, and chemical cycling of nutrients and elements - or when assessing carbon dynamics with respect to global change - modelling and simulation are necessary. Although wetlands occupy a relatively small proportion of the earth's terrestrial surface (<3%), they contain a disproportionate share of the terrestrial carbon pool (15 to 22%). Models that do not accurately represent wetland soil processes cannot, therefore, provide reasonable simulations. We evaluated 12 widely used soil C models to determine their applicability to wetland ecosystems: CANDY, CENTURY, DAISY, DNDC, ITE, MBL-GEM, NCSOIL, QSOIL, ROTHC, SOMM, VVV, and WMEM. Only three (CENTURY, DNDC, and WMEM) allow for anaerobic conditions; none contain components for anoxia, groundwater hydrology, multiple organic and physical soil layers, or a daily time-step, all of which are necessary when modelling soil C in wet soils. Accordingly, for any land area that includes wetlands, none of the individual models could produce reasonable simulations based on soil processes. We present a wetland soil C model framework based on the desired attributes, the DNDC model, and components of the CENTURY and WMEM models. Our proposed synthesis could be appropriate when considering soil C dynamics at multiple spatial scales and where the land area considered includes both wetland and upland ecosystems.