Impact of global major reservoirs on carbon cycle changes by using an advanced eco-hydrologic and biogeochemical coupling model

Recent research suggests that reservoirs might be a potentially important source of greenhouse gases to the atmosphere that is often unaccounted for in carbon cycle. The authors developed an advanced model coupling eco-hydrology with biogeochemical cycle (NICE-BGC). The model incorporates complex coupling of hydrologic-carbon cycle in terrestrial-aquatic linkages. In this study, NICE-BGC was further extended to apply to river basins to include the effect of 82 major reservoirs created by dams on hydrologic and biogeochemical cycles. The model result showed the differences in horizontal carbon transport (DOC flux = −66.4 TgC/yr, POC flux = −11.8 TgC/yr, and DIC flux = −43.5 TgC/yr) and vertical fluxes (CO2 evasion = 76.6 TgC/yr, and carbon burial = 45.0 TgC/yr) in presence of the reservoirs. The model also calculated CO2 evasion and carbon burial in global 82 reservoirs were 66.5 ± 35.9 TgC/yr and 54.7 ± 29.1 TgC/yr. Further, the result showed that the land carbon sink decreases more with the presence of reservoirs (−0.97 ± 0.61 PgC/yr) than without the presence of reservoirs (−1.05 ± 0.62 PgC/yr). These results are great improvements from previous research based on only field measurement because field measurements only accounted for emissions directly from the reservoirs and didn’t evaluate total carbon cycle. The model calculates the emission from the river downstream from the reservoirs in addition to the emission directly from the reservoirs. Therefore, the total simulated CO2 evasion increased not only in rivers with reservoirs but also in rivers downstream from reservoirs, which implies the need to include field observations of emissions from rivers downstream from reservoirs to quantify the total emissions due to reservoirs in the future. This finding provides valuable insights for re-evaluation of carbon cycle change of the biosphere in reservoirs.