Above-ground earthworm casts affect water runoff and soil erosion in Northern Vietnam

Pascal Jouquet (1) , Pascal Podwojewski (1) , Nicolas Bottinelli (2) , Jérome Mathieu , Maigualida Ricoy , Didier Orange (1) , Toan Duc Tran , Christian Valentin (1)

1 Bioemco - Biogéochimie et écologie des milieux continentaux
2 BIOSOL - Biodiversité et fonctionnement du sol

This manuscript focuses on the effects of above-ground earthworm casts on water runoff and soil erosion in steep-slope ecosystems in Northern Vietnam. We investigated the effects of Amynthas khami, an anecic species producing above-ground casts of prominent size, on water infiltration and soil detachment along a land-use intensification gradient: a cultivation of cassava (Mahinot esculenta; CAS), a plantation of Bracharia (Bracharia ruzziziensis; BRA), a fallow (FAL), a fallow after a forest of Eucalyptus sp. (EUC) and a plantation of trees (Acacia mangium and Venicia Montana; FOR). Two scales of studies were considered: (i) at the structure scale (cm2), a water runoff simulation was used to differentiate the effects of casts, free biogenic aggregates that previously belong to casts, and free physicogenic aggregates; (ii) at the station levels, 1-m2 plots were used to determine runoff and soil detachment rates during the rainy season in 2005. A. khami was sensitive to land-use management. Earthworm density was low in all the fields (0–1 ind m−2). The highest densities were found in EUC and FOR and no individual was found in CAS. As a consequence, soil surface in EUC and FOR was covered with casts and free biogenic aggregates (approximately 22 and 8 kgm−2, respectively). In FAL and BRA, casts covered the soil only sparsely with b3 kgm−2. In CAS, soil surface was characterized by free physicogenic aggregates that might be produced by human activity or endogeic earthworms through tillage (approximately 1 kg m−2). Water runoff simulation clearly showed an enhancement of water infiltration with earthworm casting activity. Water runoff was more decreased with casts (R2=0.26) than free biogenic aggregates (R2=0.49). Conversely, physicogenic aggregates were not associated with higher water infiltration. Analyses of runoff and soil detachment rates during the rainy season underlined that the more land-use type have aggregates on soil surface and the less important is surface runoff (R2=0.922). Conversely, no relation occurred between aggregates and soil detachment rate. While above-ground casting activity decreased surface runoff, they were not involved in soil detachment, and therefore soil erosion.

Mots clés: Erosion; Earthworms; Above-ground casts; Land-use change; Water runoff; Soil detachment

Domaines: Biodiversité et Ecologie

Pascal Jouquet, Pascal Podwojewski, Nicolas Bottinelli, Jérome Mathieu, Maigualida Ricoy, et al.. Above-ground earthworm casts affect water runoff and soil erosion in Northern Vietnam. CATENA, 2008, 74, pp.13-21. ⟨10.1016/j.catena.2007.12.006⟩. ⟨bioemco-00396253⟩