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

Abstract

The occurrence, as well as the environmental fate and impact, of vegetable oil spills in freshwater wetlands have until now been unreported. Thus, the largest global vegetable oil spillage in a freshwater wetland, which occurred at the Con Joubert Bird Sanctuary wetland in 2007, presented an ideal opportunity to evaluate these impacts. Five post-spill sampling sites were selected within the wetland from which a variety of abiotic and biotic samples were collected bimonthly over a period of 12 months. Abiotic variables included the sediment and water column oil concentrations, total nitrogen, total phosphorous, biochemical oxygen demand (BOD), silica, chlorophyll a, as well as in situ measurements of pH, electrical conductivity, and dissolved oxygen. Aquatic macroinvertebrates were chosen as biotic indicators in the study field due to their wide applicability as water quality indicators and were thus collected at each site. Spatial and temporal changes in total nitrogen, total phosphorous, and chlorophyll a concentrations as well as changes in pH were observed. The oil spillage also resulted in an increase in tolerant macroinvertebrate taxa, mainly Chironomidae and Psychodidae, at the sites closest to the source of the spillage. These two taxa, and to a lesser extent, Syrphidae, were identified as potentially useful indicators to determine the extent of vegetable oil contamination within a freshwater wetland. Furthermore, monitoring of these indicator taxa can be a useful management tool to determine the recovery of freshwater wetlands after vegetable oil spills. In the study, a static battery of bioassays of different biotic trophic levels was also employed to determine the adverse effects of the spilled vegetable oil on the biotic environment. It was evident from the result of the static battery of bioassay that adverse effects of the sunflower oil differ between trophic levels. The latter was in relationship with the data obtained from the field macroinvertebrate study, indicating that certain macroinvertebrate families were more tolerant to the adverse effects of sunflower oil than other families.