LAND MANAGEMENT IMPACTS ON HYDROLOGY, YIELDS, AND CONCENTRATION VS. DISCHARGE RELATIONSHIPS IN SMALL, UNGLACIATED, CENTRAL OHIO WATERSHEDS

In natural waters, concentration-discharge relationships can give insight to the link between chemical weathering and hydrological processes. Catchments with minimal human impact have hydrographs that typically display chemostatic behavior, where chemical concentrations remain constant as discharge varies, but catchments with various degrees of human impact and distinct management types have had little investigation. We have carefully scrutinized previous runoff water quality data compiled by USDA personnel from seven small watersheds (0.59 to 32.1 ha) at the North Appalachian Experimental Watershed (NAEW) near Coshocton, Ohio, USA from between 1984 and 2009. The watersheds include heavily managed agricultural sites that have shifted practices through time and sites that have consistent practices through time, including a forested site. Sites also vary in their hydrology, from runoff-only to strong influences from baseflow. Average annual yield data, enrichment factors of rainfall chemistry normalized to runoff chemistry, and log-log slopes of concentration-discharge flow values for Ca²⁺, Mg²⁺, K⁺, Na⁺, Cl^-, and NO₃^- were calculated and compared for storm events. Yields varied with flow for runoff-only watersheds. WS127 (corn- no till) produced the highest yields ranging 0.08 to 0.35 kg ha^-1 for the rainfall dominated ions Na⁺, Cl^-, and NO₃^-, which were identified by enrichment factors close to or less than 1. The yields for watersheds with baseflow are less rainfall controlled and relate increased yield to increased influence of baseflow to runoff for Ca²⁺, Mg²⁺, and Na⁺. Despite the large differences in yield and enrichment factors between heavily managed with runoff-only watersheds and less managed with baseflow watersheds, all sites exhibit close to true chemostatic flow behavior, where log-log slopes of concentration to discharge are near 0 for all ions. Further, the runoff-only sites display even stronger chemostatic behavior with slopes ranging -0.004 to -0.070 compared to the baseflow sites which ranged -0.070 to -0.163 for Ca²⁺, K⁺, and Na⁺. Our work demonstrates that intensively managed watersheds exhibit less dilution than natural catchments, yet ion yields are greatest in sites where there are groundwater additions.