PAIRING TRACERS WITH MONITORING TO IMPROVE UNDERSTANDING OF KARST SPRING COMPLEX PROCESSES

In the Salado Springs complex (Central Texas), understanding aquifer recharge and inter-spring relationships is an important part of managing groundwater for resource conservation and critical habitat. However, characterization of a spring system can be challenging due to the inherent heterogeneity and anisotropy of a fractured, karsted limestone aquifer. Partnership between researchers and local groundwater managers pave the way for dynamic research, greater access to the aquifer, and effective long-term monitoring.

This study combined tracers with water chemistry monitoring at Salado Springs, a complex of springs in the Northern Segment of the Edwards BFZ aquifer, to gain a better understanding of spring relationships. Dissolved radon-222 was used as a natural tracer to differentiate groundwater contributions to streamflow. Radon-222 is the alpha decay product of radium-226 in the uranium-238 series; and its concentration in water is related to the uranium content of source geology, residence time, and gas-phase diffusion into the atmosphere. Hydraulic connectivity of springs within the complex were evaluated with a series of dye tracer tests. Multi-parameter dataloggers were deployed at key springs to monitor water level, temperature, and specific conductance at high sampling frequencies. These data were correlated with rainfall events to give insight into aquifer recharge responses. Monitoring at multiple springs detected different system responses to recharge events and highlighted relationships among springs in the complex.

Close collaboration between researchers and groundwater managers has facilitated research, and increased awareness of groundwater conservation. Support from the local groundwater conservation district allowed more frequent site visits and greater access to sampling locations. In return researchers provided current and relevant insight on the behavior of the groundwater system, improving the quality of information used in management decisions such as well siting and the development of an effective long-term monitoring program.