茶卡盐湖沉积物和周围地区植物中正构烷烃及其氢同位素组成特征

摘要

In order to understand n-alkanes and hydrogen isotope features of sediments and organisms in typical sedimentary environment of salt lakes, n-alkanes and their hydrogen isotope compositions of sediments in the Chaka Lake and terrestrial plants in its adjacent areas were first determined using GC-MS and GC-TC-IRMS techniques. The results show that n-alkanes of the plants from the adjacent areas around the Chaka Lake exhibit a unimodal pattern with main peaks at C25 and C27, and characterize predominance of odd-carbon numbered alkanes over even-carbon ones, with average chain length (ACL) values closely related to plant types. The n-alkanes from the lake sediments have a similar distribution pattern and their features are close to those from terrestrial herbaceous plants in the studied area. The hydrogen isotopic compositions (averaged SD of -81. 7‰) of individual n-alkanes from woody plant leaves around the Chaka salt lake are heavier than those (averaged SD of -164. 3‰) of terrestrial herbaceous plants. Formation of n-alkanes derived from different plant species has different fractional distillation of hydrogen isotope. Compared with woody plants, the herbaceous plants are much more enriched in light hydrogen isotope relative to environment water. The ACL and SD values of w-alkanes from the sediments are similar to those in terrestrial Poa sp. And Kobresia sp. Herbaceous plants, indicating that w-alkanes in the sediment are derived mainly from these plants. These data and results provide a scientific basis for the application study of hydrogen isotopic compositions of individual n-alkanes.%为了认识盐湖典型沉积环境中沉积和生物中正构烷烃及其氢同位素特征,应用GC-MS和GC-TC-IRMS同位素分析技术,首次对茶卡盐湖沉积物和周围地区陆生植物中正构烷烃及其氢同位素进行了测定,研究了正构烷烃及其氢同位素组成.结果表明,茶卡盐湖周围地区植物中正构烷烃呈单峰型分布,主峰碳数为C25和C27；存在强的奇偶优势,并且碳链长度ACL值与植物的类型有关.茶卡盐湖底层沉积物中正构烷烃的分布都是类似的,其特征主要与该地区陆生草本植物的更接近.茶卡盐湖周围地区木本树叶的正构烷烃氢同位素组成较重,平均δD值为-81.7‰；草本植物的正构烷烃氢同位素组成较轻,平均δD值为-164.3‰.不同种类植物的正构烷烃合成期间具有不同的氢同位素分馏效应,与木本植物相比较,草本植物的正构烷烃相对于环境水更富集轻氢同位素.茶卡盐湖底层沉积物中正构烷烃氢同位素组成分布在-208.0‰～-107.8‰之间,平均值为-163.8‰～-127.7‰,并且高碳数正构烷烃(大于C24)平均δD值分布表现为偶碳数正构烷烃重于奇碳数正构烷烃.沉积物中正构烷烃的平均碳链长度ACL值和氢同位素组成与该地区陆生早熟禾和嵩草草本植物的相近,反映了沉积物中正构烷烃主要来自这些植物.这些资料和认识,为单体正构烷烃氢同位素应用研究提供了科学依据.