CGER Reports

CGER’s Supercomputer Monograph Report Vol. 26

Development of process-based NICE model and simulation of ecosystem dynamics in the catchment of East Asia (Part V)

NAKAYAMA T.

This monograph (Part V, CGER-I148-2019) succeeds a series of the author’s previous reports: Vol. 11 (Part I, CGER-I063-2006), Vol. 14 (Part II, CGER-I083-2008), Vol. 18 (Part III, CGER-I103-2012), and Vol. 20 (Part IV, CGER-I114-2014) published before.

The National Integrated Catchment-based Eco-hydrology (NICE) is a 3-D, grid-based eco-hydrology model, and includes complex subsystems in natural vegetation, irrigation, urban water usage, stream junctions, and dams/canals, to develop integrated human and natural systems and to analyze the impact of anthropogenic activity on eco-hydrologic change.

In the current monograph (Part V), the author reviews a new development of process-based NICE-BGC by an extension of the original NICE coupling with various biogeochemical cycle models (Fig. 1). This new model also extends to evaluate water and carbon cycles in the global and continental scales beyond East Asia in the author’s previous monographs (Part I to IV) (Fig. 2). NICE-BGC includes mechanisms of transport, mineralization, and sequestration of carbon in terrestrial–aquatic linkages, the interplay between inorganic and organic carbon and its relationship to nutrients (e.g., nitrogen and phosphorus), and the effect of hydraulic control structure such as dam on biogeochemical cycle changes.

fig.1 Flow diagram of new development of eco-hydrologic and biogeochemical coupling model along the terrestrial-aquatic continuum (NICE-BGC). The original NICE was coupled with biogeochemical cycle models such as LPJWHyMe, QUAL2Kw, SWAT, RokGeM, and CO2SYS in this new model. — **fig. 1** Flow diagram of new development of eco-hydrologic and biogeochemical coupling model along the terrestrial-aquatic continuum (NICE-BGC). The original NICE was coupled with biogeochemical cycle models such as LPJWHyMe, QUAL2Kw, SWAT, RokGeM, and CO2SYS in this new model.

fig.2 Extention of the author’s previous researches towards better understanding of the global water and biogeochemical cycles in this monograph (Part V). — **fig. 2** Extention of the author’s previous researches towards better understanding of the global water and biogeochemical cycles in this monograph (Part V).

The author introduces some results on global water and carbon flux budgets in inland water (Fig. 3), seasonal variations of global carbon flux (Fig. 4), and changes in vertical flux with the presence of reservoirs (Fig. 5). These results quantify the horizontal and vertical carbon fluxes in terrestrial–aquatic linkages, and also imply the necessity to revise existing studies mainly concentrated on the vertical carbon flux and reaction in terrestrial ecosystem.

fig.3 Global water and carbon flux budgets in inland water simulated by NICE-BGC. The model simulates horizonal carbon transport (TOC, DOC, DIC, and POC export to the ocean) and vertical carbon flux (CO<sub>2</sub> evasion to the atmosphere; CO<sub>2</sub>, and sediment storage; Bed). — **fig. 3** Global water and carbon flux budgets in inland water simulated by NICE-BGC. The model simulates horizonal carbon transport (TOC, DOC, DIC, and POC export to the ocean) and vertical carbon flux (CO₂ evasion to the atmosphere; CO₂, and sediment storage; Bed).

fig.4 Seasonal variations of global carbon flux (a) from terrestrial into aquatic ecosystems and (b) in inland water, simulated by NICE-BGC. The result shows there is a great variability of each component affected by terrestrial-aquatic continuum and aquatic metabolism. — **fig. 4** Seasonal variations of global carbon flux (a) from terrestrial into aquatic ecosystems and (b) in inland water, simulated by NICE-BGC. The result shows there is a great variability of each component affected by terrestrial-aquatic continuum and aquatic metabolism.

fig.5 Changes in vertical flux without and with reservoirs; (a) CO<sub>2</sub> evasion and (b) sediment storage affected by the height of the reservoir. The result shows the flux increases not only in a river with a reservoir (●), but also in a river downstream of reservoir (▲). — **fig. 5** Changes in vertical flux without and with reservoirs; (a) CO₂ evasion and (b) sediment storage affected by the height of the reservoir. The result shows the flux increases not only in a river with a reservoir (●), but also in a river downstream of reservoir (▲).

The evaluation of terrestrial-aquatic linkages and aquatic metabolism in this monograph is also important for the improvement in the quantification of greenhouse gas fluxes such as CO₂, CH₄, and N₂O and biogeochemical cycle, which NICE-BGC is now analyzing in more details. Currently, NICE-BGC is also developing to couple with an ocean carbon cycle model to evaluate the land-ocean interaction in global estuaries. The author hopes to report these evaluations currently being underway in a following monograph (Part VI) in the near future. These approaches will not only aid an evaluation of the complex processes involved from the view point of hydrologic and biogeochemical cycles, but will also clarify how the substantial pressures caused by water resource imbalance can be overcome by effective trans-boundary solutions.