Snow-Dependent Biogeochemical Cycling of Polycyclic Aromatic Hydrocarbons at Coastal Antarctica

Abstract

The temporal trend of polycyclic aromatic hydrocarbons (PAHs) in coastal waters with highly dynamic sources and sinks is largely unknown, especially for polar regions. Here, we show the concurrent measurements of 73 individual PAHs and environmental data, including the composition of the bacterial community, during three austral summers at coastal Livingston (2015 and 2018) and Deception (2017) islands (Antarctica). The Livingston 2015 campaign was characterized by a larger snow melting input of PAHs and nutrients. The assessment of PAH diagnostic ratios, such as parent to alkyl-PAHs or LMW to HMW PAHs, showed that there was a larger biodegradation during the Livingston 2015 campaign than in the Deception 2017 and Livingston 2018 campaigns. The biogeochemical cycling, including microbial degradation, was thus yearly dependent on snow-derived inputs of matter, including PAHs, consistent with the microbial community significantly different between the different campaigns. The bivariate correlations between bacterial taxa and PAH concentrations showed that a decrease in PAH concentrations was concurrent with the higher abundance of some bacterial taxa, specifically the order Pseudomonadales in the class Gammaproteobacteria, known facultative hydrocarbonoclastic bacteria previously reported in degradation studies of oil spills. The work shows the potential for elucidation of biogeochemical processes by intensive field-derived time series, even in the harsh and highly variable Antarctic environment.

Keywords: PAH; biodegradation; biogeochemical processes; coastal Antarctica; marine bacterial communities; polycyclic aromatic hydrocarbons.

Figure 1

Location of the sampling sites for water and plankton samples at coastal Livingston (left panel) and Deception Islands (right panel) in the South Shetlands Islands (Antarctica). Figure created using Quantarctica version 3.2.

Figure 2

Concentrations of low MW PAHs (upper panels) and high MW PAHs (lower panels) in the water-dissolved phase for the three sampling campaigns at Livingston and Deception Islands. The red line indicates the seawater temperature.

Figure 3

Relative contributions of the top 10 more abundant hydrocarbonoclastic bacteria (HCB) found in coastal waters of Livingston and Deception Islands for the three sampling campaigns.

Figure 4

Temporal trends of relative abundances of PAHs in the water-dissolved phase after normalizing to chrysene for the three campaigns. The benchmarking using chrysene blocks the influence of different inputs such as snow, allowing us to compare the different degradation for the three campaigns, with lower relative contributions at Livingston 2015 consistent with larger biodegradation. The green line shows the sum of the relative abundances of all of the PAHs, the blue line is the sum of LMW PAHs, and the red line is the sum of HMW PAHs.

Figure 5

Correlation heatmap between ASV relative abundances and environmental variables. PAH concentrations in the water-dissolved phase were benchmarked for chrysene. Positive and negative correlations are indicated with red and blue colors, respectively. Significant correlations (p < 0.05) are represented with a blue asterisk. NH₄⁺, PO₄^3–, NOxT: Inorganic nutrients. BA: Bacterial abundance. PAR: Photosynthetically active radiation. Colors on the ASV taxonomy indicate the class (Gammaproteobacteria in yellow, Alphaproteobacteria in blue, and Bacteroidia in red).