Sterols and Stanols as Indicators of the Faecal Pollution Origins at Karst Springs

Abstract:

Groundwater from karst aquifers (through springs and wells) is a major source of drinking water for at least one quarter of the world’s population. These aquifer systems are extremely complex and challenging to understand, as well as exceptionally vulnerable to pollution. Furthermore, groundwater pollution can be associated with a variety of sources making it a complicated problem to solve. In rural and suburban areas, human wastewater effluent and agricultural sources are generally considered among the most significant threats to groundwater quality. However, significant knowledge gaps exist with respect to linking pollutants with specific origins which is needed in order to quantify the various pollution impacts on karst groundwater resources. Thus, investigations of the occurrence, fate and transport (and transformations, where applicable) of source-specific contaminants are crucial for the protection and management of karst aquifers.

Faecal sterols and stanols have been found to be reliable indicators of wastewater treatment efficiency and a useful tool in the detection of contamination sources in surface water. Still, investigations of sterol and stanol concentrations and their specific ratios in groundwater systems (especially in karst environments) are extremely rare. In this study, research has been carried out on monitoring of changes in human and agricultural sterol and stanol composition in groundwater at nine karst springs over time. This has then been used to differentiate between faecal contamination of human wastewater origin from agricultural faecal pollution. The research was carried out in rural karstified watersheds in the west of Ireland for over a year. Our results indicate that this faecal source tracking method can be useful in karst aquifer systems despite the fact that concentrations of faecal sterols and stanols of interest were usually low which makes the interpretation of results challenging. Moreover, we have found that when it is not possible to calculate and interpret sterol and stanol ratios due to their extremely low concentrations in groundwater samples, the sole composition of sterols and stanols in samples over time can be used to reveal the dominant source of faecal pollution at that karst spring.