Micromorphological evidence for changes in soil faunal activity following application of sewage sludge and biocide

Soil invertebrates have the potential to induce changes in soil physical properties. We have determined the effect of sewage sludge and a biocide (chlorpyrifos) application on faunal activity in the H horizon of an upland grassland soil as expressed in the incidence of faunal excrement and related micromorphological features. This approach allows the accumulated effects of invertebrates on soil physical properties to be compared even if the organisms are no longer present or active. Sewage sludge addition resulted in an increase in faunal activity as indicated by the abundance of excrements and total porosity of the soil, but a reduction in the size of the soil microbial biomass. There were no significant effects of biocide on soil porosity, microbial biomass, or microbial respiration. Undifferentiated or fused excrements were more abundant in the biocide-treated soils, which were also distinguished by a larger amount of amorphous organic matter compared with the control, suggesting a reduced production of new excrements.