Flow and patterns of nitrate pollution in groundwater: a case study of an agricultural area in Tsukuba City, Japan

A numerical simulation was applied to first characterize the groundwater flow and patterns of nitrate pollution of a small-agricultural catchment in Tsukuba City, Japan, for a 10-year period. There was a good performance of the flow simulation. In contrast, although the transport model calculated the evolution of the plume, it only provided estimates of solute concentrations. Groundwater contamination increased exponentially during the first 594 days of the simulation, reaching then a near-equilibrium state. Fertilizer applications are responsible for most of the leaching of NO₃⁻ to groundwater, therefore, shifting of crops and the associated agricultural practices may translate into decreases of contamination levels. A series of hypothetical scenarios demonstrated that replacing grasslands by other crops may reduce the contamination levels up to 12%. As the chosen field is a representative of many other agricultural areas in Japan, the approach and results should also be applicable to similar cases around the country.