Evaluation of the groundwater capture zone for modelling of nutrient discharge

We evaluated a groundwater capture zone through both chemical analysis of g roundwater samples and numerical simulation to model the nutrient discharge by groundwater into Lake Biwa, Japan. Solute concentrations in groundwater decrease with depth near the lakeshore. The capture zone of the groundwate r was estimated by solute concentration to be deeper than 100 m below the s urface even though a clay layer exists at a depth of 10 to 20 m. Numerical simulations of changes in solute concentrations of groundwater seepage have been made using different values for the groundwater capture zone depth. C alculated concentrations agreed well with observed ones when the depth of t he groundwater capture zone is set at 150 m. The combination of the chemica l and physical evidence helped us to model nutrient discharge by groundwate r. Copyright (C) 2001 John Wiley & Sons, Ltd.