Influence of termites on runoff and infiltration: quantification and analysis

In sahelian regions, termites are the most important component of soil macr ofauna, as judged by population density and their impacts on soil structure . This paper is an attempt to quantify the effect of termite activity on in filtration in natural conditions and to provide an analysis of the various processes involved. A mulch was used to attract termites to crusted soil si tes. Runoff measurements under natural rainfall during 4 years were used to estimate the effect of termites on infiltration, which was increased by a mean factor 2-3. The relationship between the intensity of termite activity and infiltration was studied at the scale of the rainfall event. We found that although infiltration increased with termite activity, at least 30 for aging holes per square meter were necessary for the effect to be significan t. Additional experiments improved the understanding of this enhanced infil tration. Galleries and their openings were characterized by their sizes and their hydraulic properties. Tension infiltration measurements and simulate d rainfalls with aqueous methylene blue showed that the termite effect sign ificantly persisted through the degradation of the soil surface crust. In a ddition, it was shown that the influence of the large macropores made by te rmites is better described as a runoff interception process than by ponded infiltration. This conclusion has important consequences for modelling the effect of a population of large macropores on infiltration. (C) 2001 Elsevi er Science B.V. All rights reserved.