New insights into spatiotemporal source apportionment of n-alkanes under mixed scenario: A pilot study on Lake Chaohu, China

Yong He; Chen Yang; Wei He; Wenxiu Liu; Fuliu Xu

doi:10.1016/j.scitotenv.2020.140517

New insights into spatiotemporal source apportionment of n-alkanes under mixed scenario: A pilot study on Lake Chaohu, China

Sci Total Environ. 2020 Nov 10:742:140517. doi: 10.1016/j.scitotenv.2020.140517. Epub 2020 Jun 27.

Authors

Yong He¹, Chen Yang¹, Wei He¹, Wenxiu Liu¹, Fuliu Xu²

Affiliations

¹ MOE Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.
² MOE Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China. Electronic address: xufl@urban.pku.edu.cn.

PMID: 32623169
DOI: 10.1016/j.scitotenv.2020.140517

Abstract

N-alkanes are ideal molecular markers for the source apportionment of organic matter. However, the estimation of both biogenic and anthropogenic sources under mixed scenario using n-alkanes and their related proxies still remains an issue. In this study, we investigated spatiotemporal variations of n-alkanes in suspended particulate matter of Lake Chaohu for their source apportionment. Overall, Σ₂₉ n-alkanes ranged from 324.1 to 113685 ng·L^-1. C₁₇H₃₆ was the most abundant homologue and was followed by C₁₈, C₂₇ and C₂₉ homologues. Carbon preference indexes (CPIs) in most samples (at least 85%) were < 3, indicating mixed sources of n-alkanes in Lake Chaohu. Therefore, biogenic and anthropogenic n-alkanes were separated by subtraction to avoid potential bias. Our results showed Σ biogenic and Σ anthropogenic n-alkanes ranged from 14.8 to 3531.6 ng·L^-1 and 257.6 to 4938.5 ng·L^-1, respectively. For biogenic n-alkanes, their carbon-chain distributions posed a preponderant peak at C₁₇, indicating algae were the main contributors to biogenic n-alkanes in Lake Chaohu. Biogenic average chain length (ACL_bio) was developed to quantify the contributions of different biogenic sources. We recommended ACL_bio < 21 for algae dominance and ACL_bio > 26 for terrestrial plant dominance. For anthropogenic n-alkanes, their carbon-chain distribution presented obviously spatiotemporal variations. The sources of anthropogenic n-alkanes in summer and winter were typical dominances of light petroleum and incomplete fossil fuel burning/heavy oil emission, respectively. New developed proxies, anthropogenic average chain length (ACL_anthro) and the ratio of unit short- to long-carbon anthropogenic n-alkanes (L/H), are effective for quantifying the relative contributions of different anthropogenic sources. We recommend log₁₀L/H > 0.5 and ACL_anthro < 20.5 for light petroleum input dominance, log₁₀L/H < -0.5 and ACL_anthro > 26.5 for incomplete fossil fuel burning at high temperature/heavy oil emission dominance.

Keywords: Carbon–chain distribution; Lake Chaohu; N–alkanes; Proxy; Source apportionment; Spatiotemporal variations.