Soil features in rookeries of Antarctic penguins reveal sea to land biotransport of chemical pollutants

Abstract

The main soil physical-chemical features, the concentrations of a set of pollutants, and the soil microbiota linked to penguin rookeries have been studied in 10 selected sites located at the South Shetland Islands and the Antarctic Peninsula (Maritime Antarctica). This study aims to test the hypothesis that biotransport by penguins increases the concentration of pollutants, especially heavy metals, in Antarctic soils, and alters its microbiota. Our results show that penguins do transport certain chemical elements and thus cause accumulation in land areas through their excreta. Overall, a higher penguin activity is associated with higher organic carbon content and with higher concentrations of certain pollutants in soils, especially cadmium, cooper and arsenic, as well as zinc and selenium. In contrast, in soils that are less affected by penguins' faecal depositions, the concentrations of elements of geochemical origin, such as iron and cobalt, increase their relative weighted contribution, whereas the above-mentioned pollutants maintain very low levels. The concentrations of pollutants are far higher in those penguin rookeries that are more exposed to ship traffic. In addition, the soil microbiota of penguin-influenced soils was studied by molecular methods. Heavily penguin-affected soils have a massive presence of enteric bacteria, whose relative dominance can be taken as an indicator of penguin influence. Faecal bacteria are present in addition to typical soil taxa, the former becoming dominant in the microbiota of penguin-affected soils, whereas typical soil bacteria, such as Actinomycetales, co-dominate the microbiota of less affected soils. Results indicate that the continuous supply by penguin faeces, and not the selectivity by increased pollutant concentrations is the main factor shaping the soil bacterial community. Overall, massive penguin influence results in increased concentrations of certain pollutants and in a strong change in taxa dominance in the soil bacterial community.

Fig 1. Spatial display of the sampling sites and frequent maritime routes within the South Shetlands Islands [1].

All human activity locations in the region and their condition (i.e. touristic site, scientific station, specially protected site) are also listed, with the sampled penguin rookeries highlighted in bold.

Fig 2. Principal component analysis using the physical-chemical variables and element concentrations of all soil samples (n = 46).

Samples are plotted as triangles showing the sample code (see Table 1).

Fig 3. Bivariate correlations between As, Cu, Cd, Pb, Se and Zn, and the % of organic carbon in the analysed soil samples.

Note the difference in the scale of concentrations.

Fig 4. Biogenic enrichment factor in the rookeries of basic soil properties (black bars), toxic trace elements (dark grey bars) and essential trace elements (light grey bars).

Data are presented as mean ± standard error of the mean. N = 7. Only variables presenting statistically significant differences between ornithogenic soils and non- ornithogenic control areas are shown (Median test, p-value<0.05).

Fig 5. Dendrogram showing the similarity of the electrophoretic band pattern (fingerprinting made by DGGE) of the extracted and PCR amplified DNA encoding for the 16s rRNA gene sequence for samples of Vapour Col, Deception Island.

The relative contribution (% dw) of C, N and P to soil weight is shown for each sample to illustrate about penguin influence. In bold, the most penguin affected soils (CV2, CV·, CV4 and CV7), note that they cluster together.