No abstract

Analysis of results from an electrical resistivity survey, a magnetic survey, and an aquifer test performed on the Leona River floodplain in south-central Texas indicates that ground-water discharge from the Edwards Aquifer through the Leona River floodplain may be as great as 91.7 Mm 3 ⁄ year. When combined with an estimate of 8.8 Mm 3 ⁄ year for surface flow in the Leona River, as much as 100.5 Mm 3 ⁄ year could be discharged from the Edwards Aquifer through the Leona River floodplain. A value of 11,200 acre-ft ⁄ year (13.82 Mm 3 ⁄ year) has been used as the calibration target in existing ground-water models for total discharge from Leona Springs and the Leona River. Including ground water or underflow discharge would significantly increase the calibration target in future models. This refinement would improve the conceptualization of ground-water flow in the western portion of the San Antonio segment of the Edwards Aquifer and would thereby allow for more accurate assessment and management of the ground-water resources provided by the Edwards Aquifer.

No abstract

Synthetic DNA tracers provide a promising approach for tracking water because they are unique, environmentally safe, and versatile and have low detection limits. This study aimed to develop and quantify synthetic double-stranded DNA tracers using a droplet digital PCR (ddPCR) platform and compared their performance with that of uranine dye, a widely used conventional tracer for hydrological investigations. The DNA tracers were stable in distilled water at 4 °C; however, their concentrations decreased at 25 and 40 °C. The DNA tracers degraded considerably in river water following a one-phase decay pattern at different temperatures (k = 0.125–0.071 h–1). In column experiments with sand and limestone media, the DNA tracers traveled at a greater speed (RV = 0.19) and showed less dispersion (RS = 0.05) and lower mass recovery (RB = 0.26) than uranine. To demonstrate concurrent tracing, two unique DNA tracers were injected simultaneously in the column, could be detected in the same sample, and exhibited similar peak concentration times. Finally, in a field experiment, DNA tracers were deployed, could be detected in a surface stream, and exhibited earlier breakthrough in comparison to uranine. The results of this study demonstrate the feasibility of using synthetic DNA tracers for tracking water and the effectiveness of ddPCR in quantifying the tracers.

The Edwards aquifer system is one of the great karstic aquifer systems of the world. It supplies water for more than 2 million people and for agricultural, municipal, industrial, and recreational uses. The Edwards (Balcones Fault Zone) Aquifer in the San Antonio, Texas, area was the first to be designated a sole source aquifer by the Environmental Protection Agency in 1975. The Edwards Aquifer also hosts unique groundwater, cave, and spring ecosystems. This 27-chapter memoir reviews the current state of knowledge, current and emerging challenges to wise use of the aquifer system, and some of the technologies that must be adopted to address these challenges.