Factors controlling the distribution and fate of nitrate in the unsaturated zone and groundwater in a semiarid agriculture area

摘要

Overuse of fertilizers in agriculture could cause groundwater nitrate pollution. However, this is related to nitrate input, soil moisture movement (direction and rate), and depth of water table in (semi)arid areas, where nitrate can be preserved and nitrate loss by denitrification can be limited. A 18-m soil profile to water table in Daxing, Beijing shows that the nitrate is accumulated in the upper unsaturated zone and has not reached water table; and then groundwater nitrate remains at baseline level (5.6 mg/L). The soil moisture movement velocity is 0.28 m/yr based on nitrate use history. It takes another ~35 years for the moisture with high nitrate content to reach water table and pollute groundwater, to which attention should be paid in water quality management.