| Commercial development of Tonkawa Spring during early 1990s resulted in a change in water quality that primarily consisted of increased sodium, chloride, and manganese concentrations. Initially, the water quality change was attributed to reinitiation of piping erosion or natural fluctuation in water quality. However, moss-like organic matter emanating from the spring pipe, originating from a leaf-cutting ant nest overlying Tonkawa Spring, led to the hypothesis that the change was related to this material.; The purpose of this research was to identify the source of the increase in manganese concentration in Tonkawa Spring. This required an understanding of the physical and ecological processes operating within the landscape. The objectives of this research were: to determine the extent of the piping processes in the upland area from which Tonkawa Spring is discharging; to determine whether the Tonkawa Spring water quality differs from other springs in the area; to evaluate the potential for leaf-cutting ant activity to influence water quality, and to identify the interactions between physical processes and the forest ecosystem. Methods used in this research included field reconnaissance, aerial photograph interpretation, subsurface investigation, stratigraphic characterization, clay mineralogy, spring water sampling, and landscape analysis. This research also used existing data sets collected during litigation related to the change in water quality.; This research identified the upland area associated with Tonkawa Spring, an environmental setting similar to other sandflat areas extending from North Carolina to Texas, as a groundwater sapping dominated terrain. With the exception of iron and manganese, prior to the water quality change, Tonkawa Spring water was similar to water quality of other springs in the area. Iron, which occurs in other springs but not in Tonkawa Spring prior to the disturbance, may be an indicator of active sapping processes. The change in Tonkawa Spring water quality is caused by leaching of nutrients from dead organic material emplaced at depth by the ants. Reinitiation of piping erosion with commercial development removed support from the ant nest, dropping the organic matter into contact with groundwater, and causing the water quality change. |
