History of anthropogenic faece and sewage contamination to Lake Erhai in southwestern China over the past 200 years

Over the past decades, faece and sewage pollution from agricultural and industrial activities has induced severe eutrophication and ecosystem deterioration of Lake Erhai in southwestern China. Investigations on the anthropogenic faece and sewage input from both spatial and historical viewpoints are of great values for recovery strategies. In this study, we investigated fecal steroids in surface sediments from Lake Erhai collected in 2018, and found that the faece and sewage contamination is mainly from the southern region due to urban development, while the raw sewage contributes more in the northern region due to agriculture activities. We further applied fecal steroids to reconstruction of faece and sewage contamination to Lake Erhai over the past similar to 200 years. The concentrations in fecal steroids remained low during similar to 1820-1970, started to increase since the 1970s, and further increased after the 1990s, indicating a cumulative effect of contamination on the lake ecosystem by agricultural activities and urbanization practices. Diagnostic ratios of faece and sewage contamination over insitu productivity remained stable or even decreased slightly during similar to 1970-1980, and significantly increased during similar to 1980-2008, suggesting that the contamination in Lake Erhai began at the 1980s. The fecal steroid records also demonstrated that even though anaerobic sewage treatment was in process, production of raw sewage still exceeded sewage treatment after the 1980s. Considerable faece and sewage contamination in the Lake Erhai catchment from anthropogenic industrialization and urbanization, which has also been observed from various environments throughout the world, asks for further efforts on regulations to protect water quality and human life. Fortunately, governmental regulations have significantly reduced the anthropogenic faece and sewage contamination to Lake Erhai over the past decades, highlighting a crucial role of sustainable management on lake ecosystem.