Effect of water accommodated fractions of fuel oil on fixed carbon and nitrogen by microalgae: Implication by stable isotope analysis.

Effect of water accommodated fractions (WAF) of #180 fuel oil on fixed carbon and nitrogen in microalgae was studied by stable isotopes. Platymonas helgolandi ca , Heterosigma akashiwo and Nitzschia closterium were exposed to five WAF concentrations for 96 h. The δ ¹³C value of microalgae was significantly lower than that of the control group, indicated that carbon was limited in the WAF concentrations. The δ ¹³C value of microalgae appeared peak valley at 48 h in control group, corresponding to the enhanced capacity in carbon fixation during microalgae photosynthesis. The physiological acclimation capacity of microalgae was revealed by the occurrence time when the δ13C value was in peak valley, and thus the physiological acclimation capacity of microalgae decreased in the order of Nitzschia closterium > Heterosigma akashiwo > Platymonas helgolandica. Principal component analysis (PCA) were applied to the δ13C value in order to verify the "hormesis" phenomenon in microalgae. The δ13C value could discriminate between stimulatory effects at low doses and inhibitory effects at high doses. In addition, the present study also investigated the effect of the nitrogen on microalgae growth. Because microalgae could still absorb the NO 3 –N and release of NO 2 –N and NH 4 –N in present study, the nitrogen cycle in microalgae was in the equilibrium status. The δ ¹⁵N value in microalgae exhibited no obvious change with the increasing of WAF concentrations at the same time. However, due to the enrichment of nitrogen, the δ ¹⁵N value first increased gradually with the time and finally was stable. Overall, the fractionation of carbon and nitrogen stable isotopes illustrated that the effect of carbon on the growth of microalgae was more prominent than nitrogen. Stable isotopes was used to investigate the influence of WAF on fixed carbon and nitrogen in microalgae growth, providing a fundamental theoretical guidance for risk assessment of marine ecological environment. • Toxic effects of oil spill on microalgae were explored by using δ ¹³C and δ ¹⁵N. • Algae δ ¹³C indicated that carbon was limited in the WAF concentrations. • Algae δ ¹³C verify the "hormesis" phenomenon. • The NO 3 –N of three microalgae decreased with time under the different WAF. • The algae δ ¹⁵N illustrated the nitrogen cycle was in the equilibrium status. [ABSTRACT FROM AUTHOR]