Association between soil fauna activity and piping in contrasted environments

Abstract

Pedological evidences and geomorphic reasons are presented to help determining if soil fauna acts as triggering agent of piping in contrasted environments. The evidences are based on soil properties, essentially soil morphology-micromorphology, but also on soil physics, chemistry and mineralogy. In the edges near the earthen banks of old, abandoned, agricultural terraces in SE Spain, clear sequences of fauna activity (both mesofauna, e.g. tarantules, and macrofauna, e.g. rabbits and foxes) can be seen in relation with piping processes under flooding conditions (once every 4 years in average). Pipe diameters start with a few centimetres (with an estimated sediment production below 1 t ha-1 y-1) and end up with over 0.5 m pipes which usually collapse and become gully heads, causing the partial destruction of large terraces of about 1 ha (with an estimated sediment production over 100 t ha-1 y-1). However, in the Central Pyrenees, in hillslopes up to 30° covered by alpine meadow (e.g. Festuca eskia), a dense network of pipes of a few centimetres of diameter in the boundary between A and B horizons, has its origin in a well developed soil aggregation mainly due to freeze-thaw processes. Once created, this important macroporosity is used by melting waters and by voles (genus Pitymys) to form pipes. Daily subsurface flow measured in one of such pipes is over 9000 L/day and the estimated sediment production at catchment scale is 0.015 t ha-1 y-1. It is discussed that in the first case soil fauna has a triggering role for piping. However, in the second case piping is only enhanced by fauna activity from an already existent network of soil macropores. In a third case, within the Tabernas desert also in semiarid SE Spain, soil fauna doesn’t seem to play any relevant role in piping production.

Keywords

• semiárido
• prado supraforestal
• mesofauna
• macrofauna
• micromorfología del suelo