| Non-point source contamination, especially microbial pollution, has been found to be a major threat to surface and ground water systems in northwest Arkansas. The major species of microbes identified are fecal coliform, which were dominated by Escherichia coli (E. coli). Water samples collected from several natural springs demonstrated that the concentration of fecal coliform rose with the spring discharge, and then the bacterial concentration dropped dramatically prior to the recessional segment of the hydrograph. Available data also suggested that the bacteria are transported with the sediments, and the natural environment is able to sustain the bacteria. We developed two tracers, europium-labeled indigenous E. coli and lanthanum-labeled Montmorillonite clay, to test these hypotheses. The europium-labeled E. coli was prepared in two steps: (1) large biomass production of indigenous E. coli using high cell density fermentation, and (2) high cell density tagging of E. coli with europium. Montmorillonite clay (Crook County, Wyoming) was labeled with lanthanum by directly incubating pretreated clay in high lanthanum salt solution. From ICP-AES analysis, the europium and lanthanum absorption capacity by the E. coli and the clay were 15.0-mg/g and 37.95-mg/g respectively. Three field injections were carried out at Savoy Experimental Watershed (Savoy, AR) to characterize the site's groundwater flow, to compare the transport of dyes with a conservative chloride tracer, and to assess the bacterial and sediment transport. The tracers were injected in a losing stream, and collected at two resurgence springs located 1486-ft (Copperhead) and 1607-ft (tangle) from the injection point. The transport of Rhodamine WT dye was closely associated with the transport of the chloride conservative tracer for both sampling sites. In contrast, the transport of dyes was slower than the bacteria and the sediment at Langle, but faster than the bacteria at Copperhead. During storm event, the transport of sediment and bacteria was similar at the rising limb of the springs' discharge, but the concentration of bacteria showed a dramatic drop after reaching the peak concentration at both springs. We have successfully demonstrated that the newly developed bacterial and sediment tracers can be applied to study the transport of bacteria and sediment in mantled karst environment. |
