Impact of the New Zealand flatworm (Artioposthia triangulata) on soil structure and hydrology in the UK

Through north west Europe, concern has been growing in recent years about the predatory nature of Artioposthia triangulata on indigenous earthworm species. In this study, the consequence of earthworm depletion by A. triangulata on soil structure and related hydrological processes is examined. Field measurements compare differences in saturated hydraulic conductivity between sites overrun by A. triangulata and neighbouring unaffected sites. Laboratory experiments were conducted on soil cores containing worms only, worms and A. triangulata, and a control with no worms or A. triangulata. Differences in the water release characteristic and bulk density between treatments was studied. It is concluded that in the short term, infestation by flatworms and consequent depletion of earthworms will increase infiltration. However, as macropores degenerate or are removed over time, an increased risk of surface run off may result in increased pollution and flood hazards, whilst reduced drainage and subsequent waterlogging may reduce agricultural productivity in certain soils. More research into understanding the processes is required.