A Field Method for Quantifying Deep Seepage and Solute Leaching

Quantifying groundwater recharge to aquifers is necessary for agricultural and environmental research. Lysimeters are the main devices for monitoring and quantifying soil water and solute balances and transport processes. However, certain characteristics of lysimeters, high costs and limited flexibility act as restricting arguments. There is a lack of effective and reliable methods for quantifying deep seepage under undisturbed soil and for managing conditions in the field. Soil hydrology measurements provide an alternative way of analysing the soil water and matter status in situ. The method presented here aims to estimate deep seepage and solute leaching in the field based on soil hydrological measurements below the zero flux plane and a calibrated hydraulic conductivity function. This method offers simple handling, flexibility, and costs less than lysimeters. The required soil hydraulic properties are only derived from tension and water content field recordings within the measurement depth. After calibration, no further information about soil properties, weather, management and land use data is required, nor is any other data. Since 1994, the method has been successfully applied at many sites in northeast Germany. A comparison between lysimeter discharge measurements and discharge calculations has confirmed the validity of this method.