NITROGEN MOVEMENT NEAR SURFACE MANURE STORAGES

Abstract

No evidence of serious groundwater contamination by excess nutrients from solid manure storage areas that had been used for over 30 yr at the Experimental Farm, Ottawa was found in an investigation that was carried out over a period of 4 yr. One storage area was on a concrete base and the other was located on a gravel base. The water table was usually above the 275-cm depth at both sites. Two unused shallow dug wells less than 250 m from the storage areas were not contaminated by nitrate, ammonium or phosphate. Water from piezometers installed at 275- and 425-cm depths near the gravel base storage area was always low in nitrate and ammonium, but sometimes appreciable levels of nitrate were found in water from a 122-cm deep piezometer. Water from piezometers installed at 122- and 275-cm depths near the concrete base storage area usually contained nitrate and ammonium. Water from piezometers installed 213 and 241 m from the storage areas in the direction of groundwater flow contained little nitrate or ammonium. The conditions prevailing in the area and the variation in the nitrate content of the groundwater during the seasons suggested that much of the nitrate originating from the storage areas was denitrified at or near the water table.