Tracing the Temporal and Spatial Variations in the Origin of Fecal Material in Three Oklahoma Watersheds Using Sterol Fingerprints

Abstract:

Organic wastes, in particular fecal material, are qualified as one of the major causes of water quality deterioration. Their accumulation in water bodies may increase algal proliferation and eutrophication and the number of pathogenic organisms, which are responsible for many intestinal diseases especially when the water is used for recreational activities and/or as a supply for drinking water. In order to estimate the risk level associated with primary body contact in recreational water bodies, enumeration of some specific micro-organisms, such as Enterococci and Escherichia coli, are commonly used. Sterol distributions can provide some relevant information on the origin of fecal material in water system, since they are ubiquitous organic compounds and their distributions in many warm-blooded animal feces can be used as evidence for their source. In this study, we monitored fecal material contamination in three Oklahoma watersheds based on sterol fingerprints over a one-year period (2012 ~ 2013).

The sterols from sediments and water samples (sterols associated to suspended particles as well as free sterols in water) were recovered using sonication and solid phase extraction (SPE), respectively, using different organic solvents. They were then identified and quantified by gas chromatography – mass spectrometry (GC-MS) using an internal standard. The GC-MS was previously calibrated with a sterol mixture injected at different concentrations.

Our primary results show that the concentration of total sterols generally increases from the Upper Canadian < Neosho Grand < Cimarron – Upper Arkansas Basins in Oklahoma. The fecal sterols commonly represent a small proportion (<15%) within the total sterols quantified in these three basins. Their distributions show a significant contribution from herbivore feces. By means of this monitoring, we are able to determine the presence of fecal contamination and provide a better understanding on the ability of using sterol fingerprints to determine the origin of the fecal contamination. Additionally, such a sampling strategy, over a one-year period at regular intervals, enable us to track the water contamination by feces according to the seasonal climatic variations such as drought or heavy rainfall events.