Concentration/discharge Hysteresis Analysis of Storm Events at the Panola Mountain Research Watershed, Georgia, Usa

The relationship between discharge and solute concentration was investigated at the Panola Mountain Research Watershed (PMRW), near Atlanta, Georgia, between the water years 1986-2002. Applying previous work by Evans and Davies (1998), the characteristics of the hysteresis loops were used to evaluate the temporal variation of the relative contribution to streamflow of source waters including groundwater (CG), soil water (CSO), and surface event water (CSE). Twenty-six storm events were evaluated for the concentrations of acid-neutralizing capacity (alkalinity or ANC), pH, specific conductance, SO4, and Cl, yielding 116 hysteresis loops. Concentrations displayed circular hysteresis loops during most storm events, highlighting the complex relation among solutes and discharge during storm hydrographs. In general, the type of hysteresis loop generated by an individual storm and that storm’s respective component rankings correlated in a predictable manner. The solutes that have the highest concentrations in groundwater at PMRW include ANC, pH, and Cl producing concave, negative trending, clockwise and anticlockwise loops, indicating a concentration component ranking of CG >CSE >CSO. In contrast, the solute with highest concentration in throughfall and overland flow was SO4 producing positive trending, anti-clockwise hysteresis loops. Specific conductance did not produce a majority of clockwise or anti-clockwise loops; therefore, it could not utilized in the investigation. The analysis of the solute concentration data indicated that groundwater dominates stormflow in PMRW with 67% of events displaying a discharge component ranking of CG>CSE or CSO, and only 23% of events showed CSE as the largest component.