Environmental Impacts of Diesel Fuel on Bacteria and Phytoplankton in a Tropical Estuary Assessed Using In Situ Mesocosms.

Abstract

Dissolved or dispersed petroleum hydrocarbon concentrations (DDPH) were monitored in Ponggol estuary, Singapore, fortnightly from July 1999 to June 2000. DDPH concentrations ranged from 4.4 to 248.9 microg l(-1) and 0.4 to 1099.7 microg l(-1) for surface and subsurface waters, respectively and with mean concentrations of 41.01 microg l(-1) in the water column. Absorbed or adsorbed petroleum hydrocarbon (AAPH) concentrations measured in sediments ranged from 20.6 to 541.0 mg kg(-1), with mean concentrations of 148.23 mg kg(-1). In situ mesocosm studies of bacteria and phytoplankton were based on field monitoring of environmentally measured concentrations of petroleum hydrocarbons, using diesel fuel as the source of contaminant. The mesocosm comprised of 25 L clear polycarbonate carboys incubated in situ for 6 days. Water and sediments from a clean site with undetectable levels of petroleum hydrocarbons were used in controls. The treatment mesocosms comprised of mean and highest concentrations of DDPH and AAPH. The study revealed signs of acute toxicity to autotrophs viz., phytoplankton and autotrophic bacteria in treatments simulating concentrations of diesel fuel found in the sediments. A stimulatory effect was seen at lower concentrations. Bacterial heterotrophs responded positively to all concentrations of diesel fuel because of the abundance of a carbon source, reduced grazing pressure and reduced competition for nutrients from phytoplankton.

Functional and structural responses of marine plankton food web to pyrene contamination

“…Pigment analyses confirmed such a change in exposed communities; diatoms were left to dominate the 250 nmol l -1 community together with green algae, whereas prymnesiophytes and cryptophytes declined compared to the control community. This is in contrast to other findings, in which diatoms were found to be more sensitive to a mixture of hydrocarbon compounds than other algal groups (Nayar et al 2005, Sargian et al 2005. The discrepancy may be caused by the more complex contamination used in those studies, or to the 'rough' characterisation of phytoplankton communities by the pigment analyses used in this study.…”

“…Unfortunately, no microscopy data were available to verify the development of the diatom community. Towards the end of the mesocosm experiment, blue-green algae increased in the exposed communities, compared to the control community; this observation is consistent with other studies of PAH effects on phytoplankton (Bastian & Toetz 1985, Nayar et al 2005, in which cyanobacteria have been reported to be more tolerant to PAH exposure.…”

“…Bacterial abundances increased again after Day 4, first in the 25 nmol l -1 community and, after Day 10, in the 250 nmol l -1 community. Increases in bacterial abundance may reflect the released amounts of substrate (dead phytoplankton indicated by a significant decrease in chl a concentrations in the 25 and 250 nmol l -1 communities), which also has been reported elsewhere (Cretney et al 1987, Nayar et al 2005. Total bacterial activity in the exposed communities was similar to that in the control after Day 4, whereas abundance was low and specific activities were high in the 250 nmol l -1 community.…”

Plankton stress responses from PAH exposure and nutrient enrichment

“…Diatoms dominated the communities after pyrene exposure at the expense of cryptophytes and dinoflagellates, which were more sensitive to pyrene. These results are consistent with our previous study (Hjorth et al 2007), but contrary to other findings (Nayar et al 2005, Sargian et al 2005. The combination of low total photosynthetic activity and high algal specific activity up until Days 4 through 5 for Py and NuPy communities usually suggests a shift in species composition towards more tolerant species (Hjorth et al 2007).…”

Acute Toxicity of Water-Accommodated Fraction and Chemically Enhanced WAF of Bunker C Oil and Dispersant to a Microalga Tetraselmis tetrathele

“…Since microalgae are primary producers of oxygen and are a vital food source for other organisms, the effects of oil spills and cleanup efforts can greatly influence the overall status of the aquatic ecosystem (Nayar et al 2005;Gonzalez et al 2009;Gilde and Pinckney 2012). Among the microalgae with established culture techniques and a history of use in toxicity tests is Tetraselmis spp.…”