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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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A 250 t sunflower oil spill in the Con Joubert Bird Sanctuary Wetland, South Africa, was the largest global sunflower oil spill in a freshwater wetland to date. Since there was insufficient historical data for the Con Joubert Bird Sanctuary Wetland prior to the spill, variations in phytoplankton assemblages were used to indicate wetland resilience in relationship with water quality variables. From this study, it was evident that the phytoplankton biodiversity was a more reliable indicator of wetland resilience than vegetable oil concentrations measured in the water column. Vegetable oil concentrations measured in the water column varied both spatially and temporally and can possibly be linked to the passive movement of drifting oil in the water column caused by wind action and temperature changes. While we were unable to pinpoint the exact mechanisms behind the increase in phytoplankton biodiversity, the response was probably driven by the degradation of the oil by natural microbial consortiums in the wetland or a possible increase in phytoplankton grazers. Certain phytoplankton genera were found to be tolerant to the adverse effects of the oil spill. These genera include Oedogonium, Cyclotella, Spirogyra,andPlanktothrix. In general, the univariate and multivariate statistical analysis showed a low diversity and richness at sites 1, 2 and 3 during the initial sampling surveys when compared to the remaining sites. However, the phytoplankton diversity and richness subsequently increased at all sampling sites from the second sampling survey, implying that there was a shift in phytoplankton biodiversity to a more stable state.

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