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.
