2023 Volume 132 Issue 2 Pages 169-181
Numerous groundwater problems involving nitrate contamination, mainly derived from fertilizer and livestock waste, are reported worldwide. In Japan, although livestock wastes thrown in unlined pits has been banned by a law established in 1999, unlined pits still remain, causing high nitrogen discharges into groundwater. At the Tsukuba Plateau Ibaraki Pref., groundwater with more than 100 mgNO3−/L is observed just below an old unlined pit with 4.1 kgN/year of nitrogen estimated to be released from the pit. In addition, a large part of the released nitrogen is denitrified in a percolation process through a clay layer beneath the pit.
