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Ornithogenic sediments are rich in toxic As (arsenic) compounds, posing a potential threat to local ecosystems. Here we analyzed the distribution of As speciation in three ornithogenic sediment profiles (MB6, BI and CC) collected from the Ross Sea region, East Antarctica. The distributions of total As and total P (phosphorus) concentrations were highly consistent in all three profiles, indicating that guano input is a major factor controlling total As distribution in the ornithogenic sediments. The As found in MB6 and CC is principally As(V) (arsenate), in BI As(III) (arsenite) predominates, but the As in fresh guano is largely composed of DMA (dimethylarsinate). The significant difference of As species between fresh guano and ornithogenic sediment samples may be related to diagenetic processes after deposition by seabirds. Based on analysis of the sedimentary environment in the studied sediments, we found that the redox conditions have an obvious influence on the As speciation distribution. Moreover, the distributions of As(III) and chlorophyll a in the MB6 and BI profiles are highly consistent, demonstrating that aquatic algae abundance may also influence the distribution patterns of As speciation in the ornithogenic sediments. [ABSTRACT FROM AUTHOR]

• δ15N of TN and inorganic N (NH 4 + and NO 3 −) in soil, moss and aquatic microbial mat were investigated. • δ15N values of soil far outside the penguin colonies resembled those in penguin colonies. • The moss impacted by guano was more enriched in δ15N than in guano-free areas. • Aquatic microbial mat near penguin colonies was 15N-enriched, while 15N-depleted at upland sites. Penguin colonies in Antarctica offer an ideal "natural laboratory" to investigate ecosystem function and the nitrogen (N) cycle. This study assessed the spatial distribution of penguin-derived N from guano and quantitatively assessed its impact on plant N utilization strategies in Victoria Land, Ross Sea region, Antarctica. Soil, moss, and aquatic microbial mats were collected inside and outside an active Adélie penguin (Pygoscelis adeliae) colony and analyzed for δ15N of total and inorganic nitrogen (NH 4 +-N and NO 3 −-N). The soil total nitrogen (TN), NH 4 +-N, and NO 3 −-N concentrations, as well as their δ15N values were significantly higher in guano-impacted areas than those in guano-free areas, verifying that guano is an important N source at and near penguin colonies. However, even far from the penguin colonies, soil δ15N values resembled those in penguin colonies, suggesting strong spatial impacts of penguin-derived N. The moss impacted by guano was more enriched in δ15N than in guano-free areas. The δ15N values of NH 4 +-N and NO 3 −-N in soils covered with moss revealed that the moss might prefer inorganic N in the absence of guano, while the dissolved organic N would become an important source for moss growing on ornithogenic soils. Aquatic microbial mat samples near penguin colonies were 15N-enriched, but 15N-depleted at upland sites. [ABSTRACT FROM AUTHOR]