Wood ash effects on enchytraeid and earthworm abundance and enchytraeid cadmium content

Increasing use of bioenergy in Sweden will lead to an increase in the recyc ling of wood ash to forest soils. Among anticipated negative effects of woo d-ash recycling are salt- and/or pH shocks that would be detrimental to gro und vegetation and the soil biota and an increase in release of heavy metal s, in particular cadmium (Cd). In the present study, the population density of enchytraeids was used as an indicator of wood-ash effects in a series o f held experiments in stands of Norway spruce (Picea abies (L.) Karst.), or mixed Norway spruce and Scots pine (Pinus sylvestris L.), in Sweden. The a bundance of enchytraeids in wood ash, wood ash + ammonium nitrate or wood a sh + lime treatments was not significantly different from that in untreated controls. Treatment with a high dose (8 t ha(-1)) of a hardened and crushe d ash with high content of readily soluble salts caused a downward movement of the enchytraeids from the upper 0-1 cm of the soil profile. At one site the Cd content in the dominating enchytraeid species Cognettia sphagnetoru m increased in the year after ash application, but decreased again during t he following two years to the same level as in the control. The results ind icated that the earthworm population might increase after wood-ash applicat ion. It is concluded that none of the ash types used in the experiments is likely to cause any pH or salt shock to the enchytraeids if applied in dose s recommended to compensate for harvest of slash.