Effects of vegetable oil pollution on aquatic macroinvertebrate assemblage in a freshwater wetland and its use as a remediation tool

摘要

The occurrence, as well as the environmentalfate and impact, of vegetable oil spills in freshwaterwetlands have until now been unreported. Thus, thelargest global vegetable oil spillage in a freshwaterwetland, which occurred at the Con Joubert BirdSanctuary wetland in 2007, presented an ideal opportunityto evaluate these impacts. Five post-spill samplingsites were selected within the wetland from which avariety of abiotic and biotic samples were collected bimonthlyover a period of 12 months. Abiotic variablesincluded the sediment and water column oil concentrations,total nitrogen, total phosphorous, biochemical oxygen demand (BOD), silica, chlorophyll a, as wellas in situ measurements of pH, electrical conductivity,and dissolved oxygen. Aquatic macroinvertebrates werechosen as biotic indicators in the study field due to theirwide applicability as water quality indicators and werethus collected at each site. Spatial and temporal changesin total nitrogen, total phosphorous, and chlorophylla concentrations as well as changes in pH were observed.The oil spillage also resulted in an increase intolerant macroinvertebrate taxa, mainly Chironomidaeand Psychodidae, at the sites closest to the source ofthe spillage. These two taxa, and to a lesser extent,Syrphidae, were identified as potentially useful indicatorsto determine the extent of vegetable oil contaminationwithin a freshwater wetland. Furthermore, monitoring ofthese indicator taxa can be a useful management tool todetermine the recovery of freshwater wetlands after vegetableoil spills. In the study, a static battery of bioassays ofdifferent biotic trophic levels was also employed to determinethe adverse effects of the spilled vegetable oil onthe biotic environment. It was evident from the result ofthe static battery of bioassay that adverse effects of thesunflower oil differ between trophic levels. The latter wasin relationship with the data obtained from the fieldmacroinvertebrate study, indicating that certain macroinvertebratefamilies were more tolerant to the adverseeffects of sunflower oil than other families.