微藻脂肪酸在中国近海缺氧海水-沉积物界面中的降解模拟研究

Simulated Study of Algal Fatty Acid Degradation in Hypoxia Seawater-Sediment Interface Along China Coastal Area

通过一系列培养实验，模拟了有机物在中国近海季节性缺氧环境沉积物-海水界面的降解过程．以中国近海典型的赤潮藻中肋骨条藻（Skeletonemacostatum）为研究对象，对中肋骨条藻中的几种典型脂类生物标志物在不同程度缺氧海水．沉积物界面中的降解行为进行追踪．通过分析测定不同培养时间获取的不同含氧体系（氧饱和度100％、50％，25％和0％）中中肋骨条藻4种主要脂肪酸[14：0、16：0、16：1（7）、20：5]的含量，结果表明，在前2-3周4种脂肪酸迅速减少，之后则变化很慢甚至几乎不变．在不同含氧体系中4种脂肪酸的降解存在很大差异，14：0、16：1（7）、20：5经过两个月的培养，在4种不同含氧体系中几乎降解完全，而16：0在4种体系中剩余25％-35％．根据multi-G模型对4种脂肪酸降解进行定量描述，结果表明，每种化合物可以分为降解较快和较慢的部分，各化合物的平均降解速率常数kav范围在0．079-0．84d-1，14：0与16：1（7）的降解在25％含氧体系中最快，在降解最快的体系中，14：0的kav是最慢体系（含氧50％）的2．3倍，16：1（7）的kav是最慢体系（含氧100％）的1．7倍；16：0的最快降解速率出现在无氧体系中（0．17d-1），是最慢体系[50％含氧体系（0．079d-1）]的2．1倍；20：5的降解速率常数则与含氧量呈正相关．结果表明，影响中国近海缺氧海区沉积物-海水界面中中肋骨条藻中脂肪酸降解的因素除了含氧量之外，有机化合物本身的结构和性质以及环境中微生物作用等对其降解也存在着很大影响．

Series of laboratory incubation experiments were conducted to simulate degradation of organic matter in sediment-seawater interface in hypoxia enviroments along China coastal area. Under four different redox conditions （oxygen saturation： 100% , 50% , 25% and 0% ）, degradations of seveal biomarkers originated from Skeletonema costatum, a typical red tide alage along China coastal area were tracked. By analyzing concentrations of four fatty acid biomarkers [ 14：0, 16：0, 16 ： 1 （7） and 20：5 ] obtained at various sampling time, results showed that their concentrations decreased significantly after 2-3 weeks＇ incubation. Then, their concentrations changed very slowly or very little. However, degradation of the four fatty acids varied dramatically in different incubation systems. Fatty acids 14：0, 16：1 （7） and 20：5 were degraded completely in all incubation systems after two-month incubation, but 25% to 35% of 16：0 was reserved in the systems. Based on multi-G model, degradations of the four fatty acids were quantively described. The results indicated that all four fatty acids had fast-degraded and slow-degraded fractions. Their degradation rate constants （kav） ranged from 0. 079 to 0. 84 d-1. The fastest degradation of 14：0 and 16：1 （7） occurred under 25% oxygen concentrations. For these two compounds, in the fastest degradation system, their k,, values were 2. 3 folds and 1.7 folds higher than those in the slowest degradation system [ 50% oxygen saturation for 14：0 and 100% oxygen saturation for 16 ： 1 （7） ] respectively. The 16：0 was degraded fastest under the anoxic condition and slowest under the 50% oxygen saturation. The ratio of the two kav s was 2. 1. The kas of 20：5 had a positive relationship with oxygen saturations. Results of this study suggested that besides oxgen saturations, structure and features of organic compounds, roles of microbe in the envrioments and etc. might affect degradations of fatty acids in S. costatum in hypoxia sediment- seawater interface along China coastal area.