Carbon and hydrogen stable isotope ratios of nalkanes are presented for Suaeda salsa and Phragmites australis from the Yellow River Delta (YRD), China. Under unpolluted conditions, S. salsa has lighter, mean carbon isotopic composition and heavier, mean hydrogen isotopic composition than those of P. australis. The d 13 C and dD variation of n-alkane in S. salsa and P. australis between unpolluted conditions and petroleum-polluted soil conditions, is small (D 13 C S. salsa = 0.7 ± 0.6 %, D 13-C P. australis = 0.8 ± 0.7 %, DD S. salsa = 6.4 ± 11.9 % and DD P. australis = 4.8 ± 8.6 %). The plants in the contaminated area have a lighter, mean carbon and hydrogen isotopic compositions than those measured in the unpolluted area of the YRD. The lighter values of dD and d 13 C of individual n-alkanes in plants from petroleum soil may be due to the reduction of photosynthesis and slowness of water usage effectiveness caused by petroleum pollution. Therefore, the dD and d13 C values of the plants S. salsa and P. australis could be used as proxies for evaluation of petroleum-polluted environments.
a b s t r a c tIn order to compare the effects of weathering on two types of mixed oil, simulated weathering experiments were performed. The first sample was a mixture of two fresh oils and the second sample was a mixture of one fresh oil and another oil sample that had undergone a serious weathering process. Comparative studies evaluated decay rates and changes in diagnostic ratios of some fingerprinting biomarkers. Results showed that the mixing process affected the weathering rate of some compounds in the oils and also that certain diagnostic ratios are more suitable for estimating mixing proportions. A Pr/n-C 17 versus Ph/n-C 18 plot can be used to identify the end-numbers of mixed oils and the (C 13 + C 14 )/(C 25 + C 26 ) ratio is a useful diagnostic ratio to detect the degree of weathering. Finally, hopane, sterane, and alkylated PAH fingerprints were found to give useful insights about the sources of the mixed oils.
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