Stanols in the Sediments of Lake Shira (Southern Siberia) as an Indicator of Fecal Influx into the Lake in the Late Holocene

Abstract

The study of fecal compounds in lake sediments is one of the newest trends in paleolimnology. Some stanols are produced by the intestinal microflora of animals from sterols found in food. Once in water bodies, these substances remain in bottom sediments for millennia; therefore, they are biochemical indicators of fecal intake. In humans and animals, similar 5β-stanols are synthesized, but their percentages differ. The human intestinal microflora produces more coprostanol and epicoprostanol than that of other animals, so these 5β-stanols are used to reconstruct the history of the population of water bodies, as well as to assess the anthropogenic load. In the present work, using gas chromatography with mass spectrometric detection, the vertical distribution of fecal stanols and their precursor cholesterol in dated bottom sediments of Lake Shira (southern Siberia, Republic of Khakassia) for a period of about 1000 years was studied for the first time. It is shown that the relative share of coprostanol and epicoprostanol was higher in sediments corresponding to the periods when the anthropogenic load in the lake’s drainage basin was supposedly increased: during the heyday of the medieval state of the Yenisei Kyrgyz (9th–11th centuries); during the period of mass colonization by the Russian population (17th–18th centuries); and in the 19th–20th centuries, during the development of resort activities. The absolute content of all fecal stanols during the last hundred years is higher, which can be explained both by an increase in fecal inflows and by the degradation of stanols, leading to a decrease in the content of fecal stanols in the underlying core layers. The results can be useful for monitoring the efficiency of treatment facilities, as well as for identifying the historical dynamics of human presence in the lake’s catchment area.