Tracking anthropogenic inputs using caffeine, indicator bacteria, and nutrients in rural freshwater and urban marine systems.

Our objective was to evaluate the hypothesis that measurements of caffeine, nutrients, and indicator bacteria can distinguish human versus non-human sources of surface water contamination in contrasting environments. A second objective was to determine if natural sources of caffeine were significant in unpopulated areas. Caffeine was measured in an isolated wetland, and a native plant source was identified. In two rural watersheds in southwest Georgia (U.S.), caffeine was detected in tributary creeks immediately below wastewater discharge sites and within towns. However, caffeine was not found in river main streams. Thus, although natural caffeine sources exist, background levels in stream drainage networks of these rural watersheds remained below detection. The presence of caffeine and elevated nitrate in streams was associated with anthropogenic inputs and population centers, whereas bacterial indicators did not correlate to these chemical indicators and appeared to have non-human sources. In contrast, caffeine in an urban coastal lagoon was generally linked to fecal coliform abundance. We observed sporadic relationships between caffeine and other water quality indicators, possibly due to differential rates of degradation. Creeks and bayous flowing into the lagoon contained the greatest caffeine concentrations and highest amounts of bacteria, nitrate, and radon, which is an indicator of groundwater discharge.