APPLICATION OF CHEMICAL TRACERS TO INVESTIGATE THE CONTRIBUTION OF BASEFLOW TO THE DRY RUN CREEK IN CEDAR FALLS, IOWA

Fluorescein and Bromide were used as chemical tracers to study the baseflow mechanisms in an intermittent river system, called the Dry Run Creek, in Cedar Falls, Iowa. Field work was carried out in 3 different phases from mid April to the end of August, 2009. Ten different sites were sampled in the first two phases. Holes of 1.3 feet to 2.6 feet deep were dug in each site using a hand auger or a soil probe. The distance from the holes to the creek was 2 to 3 feet. Afterwards, two wells of about 15 and 20 feet deep on an on-campus monitoring well site were selected for the 3^rd phase of the study. Fluorescein in two different concentrations (0.25grams/100 ml water and 5 grams/ 100 ml water) was poured into the holes during the1^st phase and the 2^nd phase respectively. A fluorescein concentration of 10 grams/1000 ml water was applied during the 3^rd phase. Besides, 10 grams of dry Sodium Bromide (NaBr) crystals were applied during each of the 3 phases. Water samples were collected until one month after the application of tracers and then analyzed in Spectrofluorophotometer (RF 5301PC) for fluorescein and in Ion chromatograph (DX 120) for bromide. Soil samples from around the application holes were also analyzed to understand the movement of chemical tracers. Both fluorescein and bromide were not detected in any of the water samples during the first phase indicating that the tracers did not enter the creek during the first 30 days. However, soil analysis detected some movement of bromide toward the creek in site 3. In the second phase, fluorescein was detected in sites 3 and 4 at 22 and 262 hours after its application while bromide was detected in site 4 after 262 hours. Besides, soil analysis detected a little movement of bromide toward the creek in sites 2, 4, and 5. However, the subsurface movement toward the creek was very limited, implying that any chemicals in the creek are mostly due to the runoff from the surrounding areas that are dominated by agricultural fields. A greater subsurface movement was observed only when the tracer concentrations were increased. In conclusion, it is demonstrated by the data that baseflow is not the primary mechanism of stream discharge in the Dry Run Creek hydrologic system. Studies of O and H isotopes are now underway to better interpret the process.