Electro-migration of nitrate in sandy soil

Migration of nitrate to groundwater has become a serious threat in many agr icultural areas. This paper presents the results of experimental laboratory tests studying the nitrate gradient developed in response to an electrical potential. Two systems were tested; the first had no flow (closed system) and the second had flow opposite to the direction of the electrical current , A solution of sodium nitrate in sandy soil was used in both systems. The tests showed that the electro-kinetic process effectively concentrated and retained nitrate close to the anode, The movement of NO; through the soil c olumn was significantly influenced by the development of a pH gradient. Sta tistical analysis was performed to determine best-fit equations relating th e nitrate gradient to the electrical input and pH gradient, A simple one-di mensional finite difference model was used to predict the pH gradient devel oped during the electro-kinetic process. The experimental measurements clos ely agreed with the predicted spatial and temporal distribution of the nitr ate gradient for both closed and open system configurations. (C) 2000 Elsev ier Science B.V. All rights reserved.