夏季珠江口外近海沉积物/水界面营养盐的交换通量

BENTHIC FLUXES OF NUTRIENTS IN NERITIC ZONE OUTSIDE ZHUJIANG RIVER ESTUARY IN SUMMER

基于2002年夏季(7月)对珠江口外近海的生态环境调查,获取了该海域沉积物间隙水的营养盐剖面资料,估算了沉积物/水界面的营养盐交换通量,并且与实验测定的沉积物/水界面交换通量进行了对比。结果表明,沉积有机质在厌氧环境下降解大大提高了间隙水中的铵盐、磷酸盐和硅酸盐含量,导致这些营养盐总体上从沉积物内部向沉积物/水界面转移。但在该界面附近,铵盐被不同程度地硝化,所形成的硝酸盐又被不同程度地反硝化;磷酸盐和硅酸盐交换通量则受到自生矿物沉淀与溶解、吸附与解吸作用的影响,因此营养盐的净交换通量是各种物理、化学和生物作用的综合结果。模拟实验研究显示,该海区NH4+、NO3-、NO2-、PO43-和SiO44-的沉积物/水界面交换通量分别为-0.197—1.93、-0.558—0.178、-0.064—-0.009、-0.079—0.126和-6.89—7.00 mmol.(m2.d)-1。根据营养盐剖面资料计算的交换通量不仅很小,交换通量方向也往往与实验结果不符。

Contents of nutrients in sediment interstitial water and overlying water in the neritic zone outside the Zhujiang River estuary were analyzed based on the investigation in July, 2002 in this area. The average contents of NH4^＋ , NO3^-, NO2^-, PO4^3- and SiO4^4- in sediment interstitial water are 100.02, 11.68, 1.29, 6.32, and 251.65μmol · L^-1 , respectively. The sharp decrease of dissolved oxygen at sediment/water interface （SWI） and the N/P ratios in the interstitial water indicate that anoxic degradation of organic matter is responsible for the increase of NH4^＋ , PO4^3- and SiO4^4- concentrations with depth. These nutrients generally migrate upwards to SWI owing largely to gradient-driven diffusion. At the sediment/water interface, NH4^＋, NO3^- and NO2^- are significantly affected by nitrification and denitrification, while PO4^3- and SiO4^4- are affected by deposition/dissolution of authigenic minerals and sorption/desorption processes. The diffusion fluxes of nutrients calculated based on their gradients in interstitial water are much smaller in magnitude than those measured by incubation experiments, and the calculated and measured fluxes sometimes indicate contrary directions. The measured benthic fluxes of NH4^＋ , NO3^-, NO2^-, PO4^3- and SiO4^4- are -0. 197——1. 93, -0. 558——0. 178,-0.064—— -0. 009,-0. 079——0. 126 and -6.89——7.00 mmol · （m^2 · d）^-1 , respectively.