河口水华区溶解有机碳行为与机制初探

浮游植物生长与固碳之间存在紧密的联系，相关机制的研究有助于更好了解海洋碳循环的过程。一般认为，水华发生时由于浮游植物大量繁殖，溶解有机碳（dissolved organic carbon，DOC，采用高温燃烧法测定）相应增加，然而，现场调查发现，长江口和珠江口夏季中高盐度（盐度10~30）水华区DOC浓度与非水华区相近，水华区总有机碳（total organic carbon，TOC）浓度较非水华区显著增加，其中，长江口水华区TOC比DOC增加60~140 μmol/L，珠江口水华区TOC较DOC高出~110 μmol/L以上，显示固碳主要以颗粒有机碳（particulate organic carbon，POC）存在。培养结果表明藻菌混合培养条件下DOC增加只占固碳~10%（即固碳的~90%为POC），相反，无菌培养条件下DOC增量可占固碳的~80%（即固碳的~20%为POC），两个河口水华区DOC未显著增加的机制可能是由于浮游植物产生的DOC易被细菌降解所致。

Preliminary study on DOC behavior and mechanism in the estuarine bloom zones

The phytoplankton growth has a tight relationship with the carbon fixation, hence the study of mechanism can discover the process of marine carbon cycle. It is believed that dissolved organic carbon (DOC, measured by High Temperature Combustion Method) is actively released by phytoplankton to compensate for the luxury carbon uptake in the bloom zone. The study results in several bloom zones in Changjiang estuary and Pearl River estuary mid-high salinity zone (salinity ranged from 10 to 30), however, showed the similar DOC concentration in these blooms and non-bloom zones. In the meantime, the total organic carbon (TOC) discovered increased significantly, TOCs were 60~140 μmol/L and >110 μmol/L higher than DOCs in the two estuaries, respectively, indicating most of the fixed carbon existing as particular organic carbon (POC). The incubation data indicated that only 10% of fixed carbon existing as DOC (i.e., 90% of the fixed carbon existing as POC) in non-sterilized seawater; on the contrary, >80% of the fixed-carbon existing as DOC (i.e., ~20% of the fixed carbon existing as POC) in sterilized seawater, suggesting bacteria take an important role in the decomposition of the phytoplankton produced DOC in the bloom zones in the two estuaries.