Quantifying impact of anthropogenic disturbances on carbon cycle changes in inland waters by using advanced earth system model in terrestrial-aquatic continuum

Abstract:

Inland waters including rivers, lakes, and groundwater are suggested to act as a transport pathway for water and dissolved substances, and play some role in continental biogeochemical cycling (Cole et al., 2007; Battin et al., 2009). Quantifying the physical and chemical connections between land and associated fresh and coastal waters is critical for understanding the dynamics of carbon cycle in aquatic ecosystems. Recently, process-based National Integrated Catchment-based Eco-hydrology (NICE) model (Nakayama and Watanabe, 2004) was developed to couple with various biogeochemical cycle models in biosphere, aquatic ecosystems, and carbon weathering, etc. in global major river basins (NICE-BGC) (Nakayama, 2017; Nakayama and Pelletier, 2018). NICE-BGC also included the feedback between soil organic content and overland carbon fluxes, and succeeded to simulate inter-annual variations of carbon cycle in a terrestrial-aquatic continuum greatly affected by the extreme weather patterns (Nakayama, 2020). In this study, NICE-BGC was further expanded to estuary in land and ocean margins where it is generally considered to be net heterotrophic ecosystems and show significant supersaturation of CO2 (Frankignoulle et al., 1998; Regnier et al., 2013). The new model used Dirichlet boundary condition at the downstream of global major rivers by using some variables (water temperature, salinity, dissolved oxygen, nutrient, alkalinity, and pH, etc.) in coastal ocean. The author conducted sensitivity analyses of carbon cycle changes in inland water by anthropogenic disturbance agents such as accelerating hydrological cycle, increasing nutrient load, eutrophication, and ocean acidification. In particular, the model simulated the difference in carbon budget in major rivers with and without fertilizer application. The result showed variations in carbon budget in different rivers reflecting various hydrologic and biogeochemical conditions. These results helped to quantify linkages between climate forcing carbon gas (GHG) emissions and carbon fluxes from surface waters at local to regional scales, to improve earth system model and its predictability, and to reduce the range of uncertainty in the model as much as possible.