亚热带水库沉积物钻孔中有机质的历史记录及其环境意义

氢指数(HI)是重要的有机质评价参数,能够反映沉积有机质中脂肪大分子物质的相对含量,并用于反演水生生态系统的历史初级生产力,有助于研究藻类生产力对污染物的富集作用。为了探讨氢指数的环境指示作用,选择了亚热带的3座水库作为研究对象,采用Rock-Eval热解与生物标志物-中性糖方法相结合的研究技术,研究了沉积钻孔有机质的来源与特征;并结合210Pb和137Cs定年技术,综合运用氢指数和总糖含量对水库的初级生产力进行了重建。结果表明:中富营养的增塘和联安水库沉积有机质主要来源于浮游藻类,且受降解的程度较小,而贫营养的新丰江水库钻孔下层有机质主要是受降解作用或陆源高等植物等的影响。近年来,3个水库的HI值都有显著性的增加,且与其对应的总糖含量以及近50年来的滑动平均温度都高度的相关,说明这些水库都经历了气候变暖所引起的初级生产力增长。同时,升高的水库生产力扩大了沉积物剖面中重金属和多环芳烃的累积。

Historical Record of Organic Matter in Sediment Cores of Subtropical Reservoirs and Its Implication for Environmental Change

Hydrogen Index (HI) is an important parameter for organic matter evaluation. It represents the relative abundance of aliphatic macromolecular hydrocarbons to total organic matter and can be used to reconstruct the history of primary productivity. In order to assessment the reliability of HI as environmental indicator, several sediment cores from three subtropical reservoirs were collected and then analyzed by a combination of Rock-Eval pyrolysis and biomarker analysis (neutral sugars). The historical change of primary productivity in the three reservoirs was also rebuilt by using the HI values and total carbohydrate contents coupled with the 210Pb and 137Cs dating. The result shows that the sedimentary organic matter in ZT and LA reservoirs is mainly derived from planktonic algae and to some extent degraded, whereas that in XFJ reservoir is affected by higher degradation and/or higher plant input at the lower layers of the sediment core. The increasing HI values at each of the three reservoirs are positively correlated with the total carbohydrate contents and the five-year average moving temperature during the recent 50 years, suggesting that the primary productivity in these reservoirs has increased due to climatic change. Meanwhile, the increasing primary productivity has enhanced the accumulation of heavy metals or polycyclic aromatic hydrocarbons in the investigated reservoir sediments.