Abstract：
Biomarkers n-alkanes and pertinent indices in lake sediments are frequently used to infer past changes in climate and environmental conditions in and around lakes. Interpretation of n-alkane records can be confounded by a lack of understanding of the multiple factors that control n-alkanes in sediments. Here, we studied n-alkanes in sediment cores from two alpine lakes, Lakes Son-Kul and Issyk-Kul, and from terminal Lake Balkhash, in arid Central Asia to identify natural and human-mediated influences on sediment n-alkane profiles. Altitudinal differences in climate, as well as in lake trophic status, proved to be important drivers of n-alkane compositional differences in the lake sediments. In the alpine lakes, the distribution of n-alkanes was biased toward long-chain components (n-C29, n-C31, and n-C33), and showed higher carbon preference index (CPIH) values, which come from dense terrestrial plant communities, promoted by greater precipitation. In contrast, n-alkanes in the core from the terminal lake displayed higher proportions of short-chain n-alkanes (n-C17, n-C19, and n-C21) because a greater proportion of the organic matter (OM) input to the sediments was derived from algae, a consequence of higher temperatures and trophic status. In recent decades, increasing nutrient inputs from human activities have caused greater accumulation of short-chain n-alkanes in sediments of alpine, oligotrophic Lake Issyk-Kul. In Lake Balkhash, n-C20 and n-C22 alkanes are exceptionally abundant, suggesting large contributions from microbial reworking of terrestrial OM. In all three study lakes, ∑(n-C29-n-C33) was elevated in sediments that correspond to periods of intense agricultural exploitation. Moreover, expansion of agriculture from low to high altitudes resulted in both synchronous and asynchronous peaks in ∑ (n-C29-n-C33) in the studied cores, suggesting the n-alkanes faithfully record the history of agricultural expansion. These findings provide insights into applications of n-alkane proxies and the response of the lake system to climate and anthropogenic impacts.
摘要：
湖泊沉积物中的生物标志物正构烷烃和相关指数通常用于推断湖泊及其周围气候和环境条件的过去变化。由于缺乏对控制沉积物中正构烷烃的多种因素的了解，正构烷烃记录的解释可能会混淆。这里,我们研究了两个高山湖泊沉积物岩心中的正构烷烃，Son-Kul和Issyk-Kul湖，从巴尔喀什湖终点站，在干旱的中亚，以确定自然和人为媒介对沉积物正构烷烃剖面的影响。气候的海拔差异，以及湖泊的营养状况，被证明是湖泊沉积物中正烷烃组成差异的重要驱动因素。在高山湖泊中，正构烷烃的分布偏向长链组分(n-C29、n-C31和n-C33)，并显示出较高的碳偏好指数(CPIH)值，它们来自密集的陆地植物群落，由更多的降水促进。相比之下,终点湖核心中的正构烷烃显示出较高比例的短链正构烷烃（n-C17，n-C19和n-C21），因为输入沉积物的有机质（OM）比例更高来自藻类，较高的温度和营养状况的结果。近几十年来,人类活动增加的养分投入导致了高寒沉积物中短链正构烷烃的大量积累，贫化伊塞克湖。在巴尔喀什湖，n-C20和n-C22烷烃异常丰富，表明陆地OM的微生物改造做出了巨大贡献。在所有三个学习湖中，∑（n-C29-n-C33）在与农业开发密集时期相对应的沉积物中升高。此外，农业从低海拔到高海拔的扩展导致了所研究岩心中∑（n-C29-n-C33）的同步和异步峰，表明正构烷烃忠实地记录了农业扩张的历史。这些发现为正构烷烃代理的应用以及湖泊系统对气候和人为影响的响应提供了见解。
