Influence Of External Source Nitrogen And Phosphate On Inorganic Carbon Source/sink

External source nitrogen and phosphate can cause series of domino effect on entironment. It is very important to clarify the coupling relationship between nutrient and inorganic carbon system for global marine entironment. In this paper, we studied the influence of external source nutrient (nitrate and phosphate) on dissolved inorganic carbon system through simulation experiments in laboratory for the first time. Furthermore, we concluded change of inorganic carbon source and sink at South Yellow Sea and other typical seas. A series of results and viewpoint are presented as followed:1. Different nutrient form (NO3-, NH4+, NO2- and PO43-) have various impact on dissolved inorganic carbon system. At the simulated experiments, when the NO3-<188μmol/L ,NH4+<126μmol/L and NO2-<39.5μmol/L, the concentration of DIC and HCO3- significantly increased while the pCO2 decreased compared with the control groups. The concentration change of DIC,HCO3- and pCO2 inversed when the nitrogen increased to certain concentration. When the NH4+>126μmol/L and NO2->39.5μmol/L, the pCO2 increased and the water present as carbon source. At the PO43- addition groups, the concentration of DIC increased while pCO2 decreased compare with the control groups. And the seawater presents as CO2 sink. At the Ulva pertusa addition groups, the concentration of HCO3- and pCO2 significantly decreased compare with the control groups. At the same nutrient concentration level, the change of dissolved inorganic carbon system in NH4+ addition groups was higher the NO3- and NO2- groups. All the N addition groups were higher than the PO43- addition groups at the amount of dissolved inorganic carbon change. The pCO2 decreased significantly and the seawater present as CO2 sink when the concentration of NO3-, NH4+ and NO2- each was at 71μmol/L, 49.7μmol/L and 11.7μmol/L. The statistical multianalysis formulas between the increased amount of dissolved inorganic carbon system and nutrient was followed:⊿DIC=-0.937(⊿PO43-)-0.34(⊿NO3-)-0.46(⊿NH4+)+0.11(⊿NO2-)(R2=0.69, n=30,Sig.<0.05)⊿HCO3-=-1.357(⊿PO43-)-0.35(⊿NO3-)-0.57(⊿NH4+)-0.013(⊿NO2-)(R2=0.76, n=32, Sig.<0.05)⊿CO32-=0.344(⊿PO43-)+0.16(⊿NO3-)+0.18(⊿NH4+)+0.076(⊿NO2-)(R2=0.69, n=32, Sig.<0.05)⊿pCO2=-1.321(⊿PO43-)-0.12(⊿NO3-)-0.31(⊿ NH4+)-0.032(⊿NO2-)(R2=0.84, n=35, Sig.<0.01)2. The impact on dissolved inorganic carbon system by nitrogen and phosphate is mainly controlled by nutrient using of phytoplankton. The concentration change of Chl-a was various with the kinds and concentrations of nutrient. When NH4+<126μmol/L, the concentration of Chl-a increased from 2.43μg/L to 2.55μg/L with the concentration of NH4+ increased. The concentration of Chl-a decreased when NH4+>126μmol/L. When NO2->39.5μmol/L or PO43- >19.5μmol/L, the concentration of Chl-a decreased. While at the NO3- addition groups, the concentration of Chl-a was all increased. That's because the phytoplankton has different tolerance with excessive nutrient. The pCO2 decreased significantly which was consistent with the Chl-a concentration at the PO43- addition groups. The decrease extent of pCO2 was NH4+>NO3->NO2-. PO43- has the high relationship with phytoplankton'photosynthesis, so the impact on inorganic carbon was most obvious. The Chl-a concentration of nutrient addition groups compared with control (⊿Chl-a) shows a significant negative correlation with⊿pCO2 (R2 =0.75, p<0.0001). The dry weight of Ulva pertusa was increased at all groups that's because Ulva pertusa has higher tolerance with excessive nutrient. The dry weight of Ulva pertusa at NH4+ groups was higher than NO3- and NO2- groups which was consistent with nitrogen absorbing order NH4+>NO3->NO2-. The dry weight increase of Ulva pertusa at PO43- addition groups was lower than NH4+ and NO3- addition groups. The dry weight of Ulva pertusa at nutrient addition groups compared with control shows a significant correlation with⊿DIC. That's because Ulva pertusa absorb HCO3- and CO2 in photosynthesis.3. The intensity of inorganic carbon sink at most seas was enhanced by the nitrogen and phosphate enrichment in recent years. We calculated the amount change of inorganic carbon source/sink caused by excessive N and P under the relationship between inorganic carbon and nutrient. In recent years, Bohai Sea, South Yellow Sea, North Yellow Sea and East China Sea each has absorbed 0.197×106tCa-1, 0.302×106tCa-1, 0.039×106tCa-1 and 2.233×106tCa-1 for the increase concentration of N and P. The change of nutrient concentration and component was the main reason for diverse carbon flux in seas. The inorganic carbon system was significantly correlated with nutrient concentration and the amount of phytoplankton through analyzing the data of South Yellow Sea in 2006a.