Comparison of microbial indicators and seasonal temperatures as means for evaluating the vulnerability of water resources from karst and siliciclastic springs

Spring water is a critical resource in many parts of the world, however, there are few effective and efficient means of evaluating the vulnerability and sustainability of those resources. This study compares two approaches to evaluate the relative vulnerability of water sources from carbonate- and siliciclastic-sourced springs. The first approach uses a West Virginia protocol for source water assessment; the protocol uses temperature variability and bacterial indicators to identify groundwater influenced by surface water. In the second approach, near-continuous spring temperature data were modeled to quantify seasonal thermal patterns. This comparison was applied to five springs in the Appalachian Valley and Ridge Province, USA. The seasonal thermal patterns in the springs were compared to the modeled air temperature to determine thermal damping and pattern lag. Springs with the least damping and shortest lag were considered to be the most vulnerable to surface influences. In general, both approaches identified the same springs as the most vulnerable and the least vulnerable. In neither approach was the outcome controlled by the geologic unit or rock type. Although long-term data sets are needed to evaluate spring water vulnerability based on thermal patterns, those data are reasonably cost-effective to obtain, and the models require no assumptions about the flow system. The thermal lag times may also be useful in determining integrated residence times for groundwater between recharge input and spring output. These residence times may provide a means to compare the sustainability of springs when lack of data or access limit the use of more complex models.