Effects of natural (flooding and drought) and anthropogenic (copper and salinity) stressors on the earthworm Aporrectodea caliginosa under field conditions

• Published in: Applied soil ecology : a section of Agriculture, ecosystems & environment Vol. 44; no. 2; pp. 156 - 163
• Main Authors: Owojori, Olugbenga J., Reinecke, Adriaan J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.02.2010; [Amsterdam]: Elsevier Science; Elsevier
• Subjects: Agronomy. Soil science and plant productions; anthropogenic activities; Aporrectodea caliginosa; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Copper; Drought; earthworms; Flooding; floods; Fundamental and applied biological sciences. Psychology; Microcosm experiment; Mixture toxicity; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Salinity; seasonal variation; Soil science; toxicity; Zoology (interactions between soil fauna and agricultural or forest soils); South Africa; Microcosm experiment; Aporrectodea caliginosa; Mixture toxicity; Copper; Flooding; Drought; Salinity; Fauna; Toxicity; Microcosm; Submersion; Ecology; Annelida; Lumbricidae; Oligochaeta; Stress; Earthworm; Study under natural conditions; Macrofauna; Soil science; Invertebrata; Anthropogenic factor
• ISSN: 0929-1393; 1873-0272
• DOI: 10.1016/j.apsoil.2009.11.006

Laboratory toxicity tests are usually conducted under stable conditions, while exposures in the field occur under variable environmental conditions. Field studies are therefore more appropriate in understanding the effect of single or mixed pollutants in the environment. Short-term interactive effects of natural environmental factors (flooding and drought) and anthropogenic stressors (copper and salinity) on the earthworm Aporrectodea caliginosa were investigated using outdoor microcosm experiments. Specimens of the lumbricid earthworm A. caliginosa were exposed in microcosms loaded with soils with increasing salinity with electrical conductivity (EC) ranging from 0.08 to 1.05 dS m −1, with or without copper oxychloride spray treatments at recommended and elevated dosages. The experiment was conducted in August/September (end of winter) and repeated in November/December (end of spring) in the Stellenbosch area, South Africa to attain exposure under variable environmental conditions. In the soil, changes in Cu concentrations along the gradient of salinity were monitored using three methods: CaCl 2, DTPA and nitric acid extraction. Survival, weight change, and cocoon production of worms and body Cu concentrations were used as indices of interaction. None of the three extraction methods could reveal interactive effects between salinity and Cu in both seasons either because concentrations of Cu were too low or below detection limits. Copper, on its own, did not have a significant effect on the measured worm parameters during both seasons. During the winter experiment, flooding of microcosms significantly reduced the survival and affected the weight change of worms, and probably caused leaching of chemicals. Interaction between salinity and Cu had no significant effects on the measured worm parameters in winter while salinity only had a significant negative effect on weight change of worms. During spring, significant synergistic interaction between salinity and Cu occurred but only at 0.3 dS m −1 by day 14 of the exposure period. At this and higher levels, salinity had a significant individual effect on survival and weight change of worms at days 14 and 28. The results indicate that higher toxicity of salinity could be expected during the dry spring periods than during the wet winter periods which are typical for southern temperate zones.