Carbon stocks in soils of Artic cities: factors of inter- and intra-city variation

Climate mitigation strategies and targeted carbon neutrality highlight the potential of soils as important terrestrial stocks of organic carbon (C). Although global soil models and datasets (e.g., HWSD, SoilGrids, or S-world) provide information on soil C stocks’ distribution around the world, they remain biased both geographically and regarding different land-use types. Geographically, soils of high latitudes are usually underrepresented in global datasets compared to temperate or tropical climates. As for land use, the major part of soil data comes from natural and agricultural areas, whereas soils of urban areas remain overlooked or completely ignored. The research aimed to fill this gap by exploring soil C stocks and factors driving their spatial variability in the Russian Arctic zone.

Soil survey was carried out in four cities of the Russian Arctic zone: Apatity (67 N; 33 E), Murmansk (68 N; 33 E), Vorkuta (67 N; 64 E), and Norilsk (69 N; 88 E). Soils in all the cities are exposed to severe climatic conditions combined with strong anthropogenic pressure from the coal and ore mining industries. Vorkuta and Norilsk are located in the permafrost zone, whereas the soils of Apatity and Murmansk do not have the permafrost layer. In each city, 30 to 100 locations were sampled, including topsoil (0-10) and subsoil (till 100 cm) layers. In the collected samples, total and organic carbon (SOC) was measured at the CN analyzer. Bulk density and rock fraction were measured to estimate C stocks. Soil microbial (basal) respiration was measured in standardized lab conditions, and the ratio between basal respiration and SOC contents was used to analyze biodegradation coefficients and half-life time. Spatial patterns of SOC distribution, including inter- and intra-city variability were analyzed by factorial ANOVA.

SOC stocks in Arctic cities were quite heterogeneous with a coefficient of variance of up to 100%. Topsoil SOC stocks were similar or even higher compared to the data reported for Russian cities in temperate climates (e.g., Moscow, Saint-Peterburg, or Ekaterinburg). Subsoil stocks were significantly lower compared to topsoil due to a gradual decrease of SOC contents with depth and a high amount of gravel and rock fragments. Elevation, vegetation, and proximity to the sources of anthropogenic disturbance were the main factors driving the intra-city variability. The difference between the cities depended on bioclimatic conditions including permafrost. On average SOC stocks in cities with permafrost were significantly higher compared to those in cities without the permafrost layers. One of the possible reasons can be the conservation of organic matter in subsoil horizons when the mineralization of organic matter is hampered by low temperatures and low microbial activity. Indirectly this statement is confirmed by higher half-life time values, although the difference was not always statistically significant.

Under climate changes the role of Arctic soils in carbon balance will further increase, therefore the research outcomes are highly relevant to develop the strategies of sustainable urban development in the region.

Acknowledgements This research was supported by RSF # 19-77-30012 and RUDN University Strategic Academic Leadership Program