DESCRIPTION OF TRACER TRANSPORT THROUGH MOIST AND DRIED SOIL COLUMNS USING A BIMODAL CDE APPROACH

作者：Spangenberg Andrea^*; Nagarajarao Yalamanchi; Hinz Christoph

来源：Fresenius Environmental Bulletin, 2011, 20(3): 616-622.

• tracer transport
• bimodality
• CDE
• dispersion coefficient
• dispersivity
• BTC

Ten undisturbed soil monoliths were collected and irrigated with bromide tracer (KBr) to investigate tracer transport under different initial conditions. Some columns were left at their natural humidity and some were oven-dried. A fixed amount of tracer was applied to the humus layer, creating three experimental variants: application of tracer of low concentration to (i) humid and (ii) dry columns and of ten times higher concentration to (iii) dry columns. Breakthrough curves (BTC) indicate different pore water velocities as well as dispersion coefficients. The recovery rate of the last experiment (dried soil and high tracer concentration) is lowest (mean: 57%). At the peak of the breakthrough merely 1.6% of the original tracer concentration reached the bottom of the columns. Breakthrough curves of dried columns show generally steeper peaks and longer tailing. Data was fitted using an analytical solution of the convection dispersion equation (CDE). Different approaches were tested. A bimodal estimation resulted in best fit i.e. optimal results. It supports the idea of two overlaying transport phenomena, a fast one through macropores and a slow one through micropores. Dispersion and dispersivity values of the slow breakthroughs are generally higher than those of the fast. Slow breakthroughs show higher heterogeneity of flow paths. Dispersion values of both breakthroughs with high concentration on dried columns (type 3) showed the same level, thus similar flow paths.

• 出版日期2011