Vegetation increases carbon and nitrogen content in riparian soils along high-Arctic headwater streams

Riparian soils are active sites of biogeochemical cycling of carbon (C) and nitrogen (N) at the interface between land and stream with further downstream impacts on coastal ecosystems. Under a warmer climate and greener Arctic, it is essential to increase our understanding of how changes in riparian vegetation cover may influence C and N content and potential runoff to the streams and downstream ecosystems. We sampled riparian topsoil (0–10 cm) and deep soil (>10 cm) adjacent to 17 headwater streams with low (<20%) to high (>60%) vegetation cover at two High-Arctic areas: Northeast Greenland and Svalbard. Our results showed that the C and N content in riparian soils are low (soil organic C median of 1.7%, total N median of 0.1%) relative to previous studies of permafrost soils. Nevertheless, organic C and total N as well as water extractable dissolved organic carbon (DOC) concentrations, were higher in riparian soil with high vegetation cover compared to low cover sites. In contrast, there was no overall difference in water extractable dissolved inorganic nitrogen (DIN) concentrations between sites with high and low vegetation cover. However, ammonium (NH₄⁺) concentration was higher at high vegetation cover. Overall, our data suggests that larger content of total organic C, total N, and DOC are available for runoff in riparian soils with higher vegetation cover, whereas no difference in the content of soil DIN and water extractable dissolved organic nitrogen (DON) was apparent among the riparian sites. Our results suggest that increased extension of vegetated areas in High-Arctic under a warmer climate will increase C and N available for runoff to streams potentially influencing stream ecosystem function, food web structure, and the export of nutrients to coastal areas.