The eutrophication process of Lake Dianchi: evidences from the δ<sup>13</sup>C value of the bound nC<sub>16:0</sub> fatty acid

Abstract

以云贵高原浅水湖泊滇池作为研究对象,在对湖心一个63cm柱状沉积物中δ¹³Corg、δ¹³N、C/N比值和TOC含量测定的基础上,以近现代沉积物有机质中结合态脂肪酸的组成及其单体碳同位素组成结果为主要的讨论对象,并与相应游离态脂肪酸的组成及碳同位素值进行了对比研究,探讨近二百年来滇池湖泊的富营养化过程.研究结果表明,沉积物中有机质基本参数变化按沉积深度可以划分成三个主要阶段,其中20cm至表层段,δ¹³N、TOC显著增大,与该时期湖泊富营养化密切相关.结合态脂肪酸总含量为38.5-209.6μg/g,游离态脂肪酸总含量为12.0-318.1μg/g,都在表层段20cm出现迅速增加的趋势;利用脂肪酸单体分子组合CPIA、∑C₂₀-/∑C₂₁₊、TARFA、C_18:1w7/C_18:1w9、(i-C_15:0+a-C_15:0)/nC_15:0比值的特征变化,表明其以内源的浮游生物和细菌输入为主,内源藻类的大量繁殖,导致湖泊富营养化加剧.相比游离态脂肪酸,滇池沉积物中的结合态脂肪酸具有较丰富的不饱和脂肪酸和正反异构脂肪酸,且具有较强的稳定性,能抵抗早期化学和生物降解作用的影响,具有重要的研究价值,将成为近年来研究的热点.结合态脂肪酸中C_16:0的δ¹³C变化较好地记录了近几十年来湖泊富营养化过程的加剧,可作为反映湖泊重富营养化进程的一个重要指标.;The purpose of this study is to investigate changes in sedimentary environments in Lake Dianchi, a shallow water lake on the Yun-Gui Plateau. Overall characteristics of organic matter values, including δ¹³Corg, δ¹³N, C/N and TOC, from a 63cm-long core from the center of the lake were analyzed. Concentrations and stable carbon isotopic compositions of the bound fatty acids are also analyzed and compared with those of the corresponding free fatty acids. The results indicate that the past environment changes recorded in the modern sediments in Lake Dianchi can be divided into three main stages. Values of δ¹³N and TOC increased during the latest stage of the 0-20cm interval and were related with the eutrophication process of the Lake Dianchi, when concentrations ofbound fatty acids and free fatty acids range from 38.5-209.6μg/g and 12.0-318.1μg/g, respectively. Compared to free fatty acids, bound fatty acids in the sediments of Lake Dianchi have more abundant unsaturated fatty acids, iso- and anteiso-branched fatty acids, indicating that they predominantly sourced from the plankton and bacteria and were more resistant to the early chemical and biological degradation. Multiplying of the plankton and bacteria caused the speeding up the lake eutrophication processes. Changes in the δ¹³C value of the bound nC16:0 fatty acid were recorded well in Lake Dianchi sediments and provided good information of the enhancement of lake eutrophication in the recent few decades. Therefore, it will become an important indicator reflecting the lake hyper-eutrophication.