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 fresh water 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 bi-monthly over a period of 12 months. Abiotic variables included the sediment and water column oil concentrations, total nitrogen, total phosphorous, 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 field study, due to their wide applicability as water quality indicators, and collected at each site. Spatial and temporal changes 2 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, the 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 were also employ 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 was more tolerant to the adverse effects of sunflower oil than other families.

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An investigation on the effect of a vegetable oil spill was conducted on the biological diversity of the Con Joubert Bird Sanctuary wetland in South Africa before and after biostimulation with different concentrations of fertilizer during 2008. Biostimulation responses were analyzed 30 days after different concentrations of fertilizer were applied to the freshwater wetland at three selected sampling sites. The Con Joubert Bird Sanctuary wetland showed a high degree of contamination after a vegetable oil spill, resulting in a large volume of vegetable oil in the sediment and water column, respectively. Vegetable oil contents differed at each sampling site before biostimulation and each site showed variable responses after biostimulation. In this study, biostimulation results displayed a high yield of microbial activity and vegetable oil degradation at site one and two respectively. However, the degradation of the high vegetable oil concentrations within the sediments at sampling site 3 may have been hampered or retarded by the polymerized state of the vegetable oil. The phytoplankton, protozoan, macroinvertebrates and microorganisms assemblage were affected and showed little improvement at site 3, even after biostimulation with the high fertilizer concentration of 800 g/m 2 , in comparison to sites 1 and 2 which showed greater biological activities and degradation of vegetable oil.