Impacts of climate warming and permafrost thaw on the riverine transport of nitrogen and phosphorus to the Kara Sea

Abstract

Measurements of nitrogen and phosphorus (N and P) concentrations from previously unstudied streams and rivers throughout west Siberia suggest that climate warming and/or associated permafrost thaw will likely amplify the transport of N and P to the Kara Sea and adjacent Arctic Ocean. We present concentrations of dissolved organic nitrogen (DON), ammonium (NH4‐N), nitrate (NO3‐N), total dissolved nitrogen (TDN), and total dissolved phosphorus (TDP) from 96 streams and rivers within the Ob'‐Irtysh, Nadym, and Pur river drainage basins. The sampled sites span ∼106 km2, a large climatic gradient (∼55°N–68°N), and include 41 cold, permafrost‐influenced and 55 warm, permafrost‐free watersheds. Concentrations for all measured watersheds average 765 μg L−1 (DON), 19.3 μg L−1 (NH4‐N), 36.7 μg L−1 (NO3‐N), 821 μg L−1 (TDN), and 104 μg L−1 (TDP). Our results show no statistically significant difference in dissolved inorganic N (NH4‐N and NO3‐N) between permafrost‐influenced and permafrost‐free watersheds. However, we do find significantly higher concentrations of DON, TDN, and TDP in permafrost‐free watersheds (increasing as a function of watershed peatland coverage) than in permafrost‐influenced watersheds. When combined with climate model simulations, these relationships enable a simple “space‐for‐time” substitution to estimate possible increases in N and P release from west Siberia by the year 2100. Results suggest that predicted climate warming in west Siberia will be associated with ∼32–53% increases in DON concentrations, ∼30–50% increases in TDN concentrations, and 29–47% increases in TDP concentrations as averaged across the region. While such increases in N and P are unlikely to significantly influence primary production in the Kara Sea as a whole, they will likely have large local impacts in the Ob' and Yenisey bays and nearshore environments.