Laboratory methods of estimating the retardation factor of migrating mineral nitrogen compounds in shallow groundwater

The retardation factor (R) is a measure of the ground's ability to restrain the migration of particular nitrogen species. It shows how many times the migration of the substance is subjected to adsorption slower than the actual speed of water flow in the pore spaces. Analysis of this factor is described for the two main forms of mineral nitrogen in groundwater, nitrate and ammonium ions, in soils typical of the area of the Kurpie outwash, in northeastern Poland. Retardation factor values have been determined by laboratory static methods, for various concentrations of these ions in water. For most soil types, the retardation factor values for nitrates, determined for various concentrations of these ions, show little variation. For soils developed from outwash sands the results obtained fall between 1.98 and 4.74; for outwash sands-1.17- 2.68; for clayey sands-2.75-6.94; and for sandy clays -7.4-26.54. The highest values 16.31-42.53 were obtained for sands enriched in iron oxides and hydroxides. A substantially higher variation in the retardation factor is shown by ammonium ions. The values determined vary between 9.4-41.4 for outwash sands, 37.6-84.8 for sands enriched in ferruginous oxides and hydroxides, 72.5-327.4 for sandy soils, 466-1043 for clayey sands and 2326-3772 for sandy clays.