COS 111-9
Evaluation of global carbon cycle in inland water through construction of advanced process-based model
Inland water might act as a gigantic transport pathway for both water and substance and play some role in continental biogeochemical cycle although its contribution has remained uncertain yet due to a paucity of data (Battin et al., 2009). The author has developed process-based National Integrated Catchment-based Eco-hydrology (NICE) model (Nakayama, 2008a-b, 2010, 2011a-b, 2012a-c, 2013; Nakayama and Fujita, 2010; Nakayama and Hashimoto, 2011; Nakayama and Shankman, 2013a-b; Nakayama and Watanabe, 2004, 2006, 2008a-b; Nakayama et al., 2006, 2007, 2010, 2012), which incorporates surface-groundwater interaction, includes up- and down-scaling processes between local, regional and global scales, and can simulate iteratively nonlinear feedback between hydrologic, geomorphic, and ecological processes. In this study, NICE was extended to evaluate global hydrologic cycle by using various global datasets. Because the original NICE incorporates three- dimensional groundwater sub-model and expands from one- or two-dimensional and steady state, so-called 'equilibrium', this advanced model can simulate the lateral transport of groundwater more pronounced at steeper-slope regions or riparian/floodplain with frequent surface-groundwater interaction in global scale. NICE was further developed to incorporate biogeochemical cycle including reaction between inorganic and organic carbons (DOC, POC, DIC, pCO2, etc.) in biosphere (terrestrial and aquatic ecosystems including surface water and groundwater).
Results/Conclusions
The river discharge and groundwater level simulated by NICE agreed reasonably with those in previous research (Fan et al., 2013) and extended to clarify further eco-hydrological process in global scale though the resolution at 1.0 ° grid was coarser than that in the previous one at 30 arc-second grid. In particular, this improvement indicated lateral subsurface flow also has important role on hydrologic and biogeochemical cycles even in continental scale (Nakayama, 2011b; Nakayama and Shankman, 2013b). This extends traditional 'dynamic equilibrium' with atmospheric forcing (Maxwell and Kollet, 2008). This revised model further included carbon cycle between river, lake, groundwater, and the terrestrial ecosystem accompanied by the hydrologic cycle there. The missing role of carbon cycle simulated by NICE, in particular, CO2 evasion from inland water (global total flux was estimated as about 1.0 PgC/yr), was relatively in good agreement in that estimated by empirical relation using previous pCO2 data (Aufdenkampe et al., 2011; Global River Chemistry Database, 2013). This advanced simulation system would play important role in identification of full greenhouse gas balance of the biosphere and spatio-temporal hot spots for boundless biogeochemical cycle, and bridging gap between top-down and bottom-up approaches (Cole et al. 2007; Frei et al. 2012).