To investigate the influence of urbanization on the component features of dissolved n-alkanes (D-ALK) in the underground river in the dry season, water samples were collected respectively at the outlet of the two underground rivers. Components of D-ALK in these samples were quantitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that the distribution of D-ALK carbon number at the two sites ranged from nC14 to nC35 in dry season. The total concentration of D-ALK (DT-ALK) in Jiangjia spring ranged from 102 to 356 ng·L-1, with an average of 230 ng·L-1. The low-number carbons were predominant in December 2014, January and April 2015. The ratios of LMH/HMH (nC21-/nC22+) ranged from 2.0 to 10. The carbon preference index (CPI) between nC14 and nC25 ranged from 0.19 to 0.57, with a maximum of C16 (Cmax16). However, in November 2014, February and March 2015, these samples had a bimodal distribution in n-alkane. All of the CPI14-25 and the ratios of LMH/HMH were less than 1. The CPI24-35 ranged from 1.2 to 23 with the Cmax 31 or Cmax33. During the three months, the values of Paq were 0.2, 0.7 and 0.1, respectively. The alkane indexes (AI) in November 2014 and March 2015 were 0.95 and 0.98, respectively. The values of DT-ALK in Laolongdong ranged from 110 to 697 ng·L-1 with an average of 310 ng·L-1. The carbon number distribution of each month had a low predominance, and the CPI14-25 was less than 1. In the dry season, under the influence of different human activities, the content and component of D-AKL in Laolongdong which originated mainly from microorganisms was more stable than that in Jiangjia spring, which was mainly derived from microorganisms and a mixture of microorganisms and plants.
Keywords: biomarkers; dissolved; karst underground river; n-alkane; urbanization.