珠江口夏季水体中的氮和磷

N and P in waters of the Zhujiang River Estuary in summer

根据1999年7月17～28日于珠江口现场调查和实验的资料,研究夏季水体中氮、磷的分布、形态变化和初级生产力的限制因素.结果表明该海域氮含量高,N/P属于世界上高值区之一.从河口向外海运输过程中,氮和磷的形态和浓度均有剧烈的变化.虽然氮在中途中有新源的补充;但由于外海水的入侵稀释、生物吸收和形态变化的迁移作用,NO-3和可溶无机氮的浓度总的变化趋势仍是随盐度增大而大幅度地降低,以至珠江口外出现N/P低于16.由于夏季水体层化稳定,在表、底层其生物地球化学变化方向相反,PO34的浓度变化互成镜像关系并可按盐度分为3段不同特征的反应区.初级生产力的限制因素在大部分区域是磷,但从口门至最大浑浊带和口外区则分别是浊度(或光照)及可溶无机氮.现场培养实验再现了真光层和底层氮和磷的生物地球化学过程差异并表明磷的循环和再生比氮迅速;在可溶无机氮浓度大且高N/P的海域,磷的再生可成为水华的引发因素,而氮被耗尽却是水华消亡的原因.总体上夏季该区水体氮的迁出率比磷高.于水体层化稳定的区域,氮和磷的生物地球化学作用在真光层以浮游生物吸收占优势、在下层以有机物的降解和可溶无机态的再生为主,当层化消失、上下水体充分混合则可完成循环.

Based on the data obtained by field survey and experiments of the Zhujiang River Estuary during July 17～28, 1999, the cycle, regeneration and restriction of N and P in water masses are studied. The results show that there is a large content of N in the Zhujiang River Estuary waters, and it belongs to a high N/P area in the world. With the water mass transported from river to sea, the speciation and concentration of N and P present a violent variation in the waters. Among others, there is new supply on the N, and the supplemental volume may be even larger than the absorbing capacity of plankton photosynthesis somewhere. Because of plankton absorbing, migration action of species variation and being intruded and being diluted by the seawater, the concentration of DIN was so constantly reduced and that the N/P was even lower than 16 off the Zhujiang River Estuary. The variation of concentration of PO^(3-)_4 become mirror image each other between the surface layer and the bottom layer water,which indicates that both the directions of biogeochemical action of P are contrary. The plankton absorbing is primary process in the surface layer, but the regeneration takes precedence in the middle layer and the bottom layer. Comparatively speaking, one point is the migration ratio of DIN is greater than DIP and the other is the turbidity (or light), P and N are the limit factors of the primary productivity in three areas (from the river gate to the maximum turbidity zone, middle waters of the estuary and off the estuary) respectively. The results of incubation show that the bloom of plankton lead to the considerabl decrease of concentration of DIN, but the concentration of PO^(3-)_4 is in a small scope vibration and keeps a more steady concentration level. It is inferred that the cycle and regeneration of P are more rapid than N, and the regeneration of P can direct supply primary product in euphotic and become a factor bringing to the plankton bloom in the waters, but the reason of the bloom passing away is the DIN being used up in the end. Through contrast study of biogeochemical cycle of N and P, similarities and differences of the process of cycle and regeneration between N and P are explicated, and infer potentiality of the denitrification action in the hypoxia area is inferred