Using fecal sterols to assess dynamics of sewage input in sediments along a human-impacted river-estuary system in eastern China

Abstract

Sedimentary fecal sterols and other sterol biomarkers, combined with bulk total organic carbon (TOC) and its stable carbon isotope were applied to characterize the sewage contamination across a ca. 280 km transect from the Xiaoqing River to the Laizhou Bay, a typical river-estuary system subjected to extensive anthropogenic stress due to rapid regional urbanization and industrialization in eastern China. Two sampling events were performed in both spring and summer seasons in the Laizhou Bay adjacent to the Xiaoqing River in order to assess the potential seasonal variation. Fecal sterols such as coprostanol and epicoprostanol, which are typical indicators of anthropogenic sewage input, displayed high concentrations of up to 63.2 μg g dry weight (dw) and 13.1 μg g dw, respectively. Results suggested that most of the stations along the Xiaoqing River were severely contaminated by fecal inputs with a decreasing trend from the river to the estuary that was mainly explained by the increasing distance from the diffuse sewage sources and the gradual dilution by sea water. Although there was no significant difference in fecal sterol concentrations between spring and summer in the Laizhou Bay, suggestive of no significant difference in sewage abundance, significantly higher average epicoprostanol/coprostanol and lower coprostanol/epicoprostanol ratios were observed in spring than summer, indicative of different sewage sources (e.g., human vs. non-human). Seasonal discharge and land-runoff, air temperature related to microbial activity differences and different extend of animal manure irrigation during agricultural planting could be additional reasons and need further investigation. Nevertheless, fecal sterol concentrations, distributions and diagnostic ratios should all be taken into consideration to better understand sewage inputs and source dynamics in river-estuary ecosystems.

Distributions and Sources of Sedimentary Sterols as well as Their Indications of Sewage Contamination in the Guanting Reservoir, Beijing

“…However, the proportion of coprostanol in the total sterol content was comparatively low, ranging from 1.4% to 9.7% with the average proportion of 4.8%. e highest coprostanol concentration detected in this study (1.24 μg g −1 ) was much lower than that observed in some heavily polluted rivers, such as the Xiaoqing River close to Laizhou Bay in eastern China (63.2 μg g −1 ) and the Pearl River (53 μg g −1 TOC) [30,41]. e concentrations of epicoprostanol ranged from 0.10 μg g −1 to 1.49 μg g −1 , with an average of 0.46 μg g −1 .…”

“…Coprostanol was widely distributed in sediments of the reservoir, ranging from 0.11 μg g −1 to 1.24 μg g −1 , with the average concentration of 0.51 μg g −1 , which was similar to the concentrations of coprostanol in sediments of rivers of Serbia and Ulungur Lake in northern Xinjiang [39,40]. Generally, the concentration of coprostanol has been used to assess the sewage pollution level, and the maximum threshold of sewage contamination used in previous studies was 0.7 μg g −1 [20,30]. Hence, we considered 0.7 μg g −1 as the threshold of sewage contamination in our study.…”

“…Besides individual sterol contents, sterol ratio parameters are widely used to more robustly evaluate the sewage contamination [30,40,42]. In this study, five sterol ratio parameters were used, including coprostanol/cholestanol, Journal of Chemistry 5 coprostanol/(cholesterol + cholestanol), epicoprostanol/ coprostanol, coprostanol/(coprostanol + cholestanol), and coprostanol/cholesterol.…”

“…In the study of source analysis using sterols, the researchers have found that besides concentrations of individual sterols, the ratios of sterols can be used as more robust indicators to assess the sewage contamination, such as sources of pollution and treatment of sewage [25][26][27][28][29][30]. e most common ratio parameters are the ratios between coprostanol, epicoprostanol, cholesterol, and cholestanol.…”

Spatiotemporal variability of hydrocarbons in surface sediments from an intensively human-impacted Xiaoqing River-Laizhou Bay system in the eastern China: Occurrence, compositional profile and source apportionment

“…Sampling sites were selected to provide a wide spatial coverage of the Xiaoqing River to Laizhou Bay system (Fig. 1, Table S1; He et al, 2018). In total, 33 surface (top ca.…”