Impacts of human and herbivorous feces on lake surface sediments of the Tibetan Plateau based on fecal stanol proxies

Lake ecosystems on the Tibetan Plateau (TP) are highly susceptible to external input owing to their fragile environment. However, less study has been done to focus the direct influences of anthropogenic activities on the lake sediments by human activities. In this study, we performed the first large-scale investigation to use the fecal stanol proxies in lake surface sediments to assess the impact of human and herbivorous feces on TP lakes. The 75 investigated lakes were divided into three types (I, II, and III) according to cluster analysis of the fecal stanol ratios R1′ and R2′. Fecal stanols in type I lake surface sediments originate from a mixture of herbivorous and human feces; fecal stanols in type II lake surface sediments primarily originate from herbivorous feces with minimal human feces. In contrast, fecal stanols in type III lake surface sediments are mainly derived from herbivorous feces (coprostanol concentration > 100 ng/g), a mixed source of herbivorous feces and cholesterol reduction (coprostanol concentration of 10–100 ng/g), and in situ reduction of cholesterol (coprostanol concentration < 10 ng/g). Among the TP lakes investigated, 9 % had significant fecal contamination, 48 % had moderate or slight fecal contamination, and 43 % were uncontaminated. Domestic animal feces were the main source of fecal stanols in the surface sediments of moderately and slightly contaminated lakes in the central TP. There were 9 % of investigated lakes with significant fecal contamination from human and herbivorous feces; in contrast, 52 % of investigated lakes did not definitely show the presence of human fecal matter. This study has important implications for fecal contamination assessment in lake ecosystems and provides a reference for early herbivorous change and paleo-human activity research.