2025-08-29 ニューヨーク大学 (NYU)
＜関連情報＞
- https://www.nyu.edu/about/news-publications/news/2025/august/climate-change-is-altering-nitrogen-composition-in-arctic-rivers.html
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2025GB008639
北極圏の大河における窒素収量の組成変化は気温と降水量に関連している Changes in the Composition of Nitrogen Yields in Large Arctic Rivers Linked to Temperature and Precipitation
Bridger J. Ruyle, Julian Merder, Robert G. M. Spencer, James W. McClelland, Suzanne E. Tank, Anna M. Michalak
Global Biogeochemical Cycles Ppublished: 24 July 2025
DOI:https://doi.org/10.1029/2025GB008639
Abstract
Global trends in river nitrogen yields reflect human distortion of the global nitrogen cycle. Climate change and increasing agricultural intensity are projected to enhance river nitrogen yields in temperate watersheds and impair downstream water quality. However, little is known about the environmental drivers of nitrogen yields in major Arctic rivers, which have experienced rapid climatic changes and are important conduits of nutrients and organic matter to the Arctic Ocean. Here we analyze trends in nitrogen yields in the six largest Arctic rivers between 2003 and 2023 and develop generalized additive models to elucidate the watershed characteristics and climatic processes associated with observed spatial and interannual variability. We found significant increases in dissolved organic nitrogen yield and/or declines in dissolved inorganic nitrogen yield in four of the six rivers. While temperature and precipitation, via their relationships to discharge, enhance dissolved nitrogen yields, we attribute the diverging trends to the responses of inorganic and organic nitrogen to temperature via effects on permafrost free extent. Spatially, we attribute differences in nitrogen yields across watersheds to differences in land cover and temperature. Shifts in the amount and composition of river nitrogen yields will impact the balance between primary productivity and heterotrophy in nitrogen limited coastal Arctic Ocean ecosystems. Results from this work highlight the importance of climate-driven changes in temperature and precipitation on river nitrogen yields in large Arctic rivers and motivate further investigation into how permafrost loss and hydrological shifts interact to drive water quality and biogeochemical cycling in the region.
Plain Language Summary
The amount of nitrogen transported by rivers impacts water quality and ecosystem structure. Excessive nitrogen loads can impair water quality, whereas depleted nitrogen loads can result in nutrient limitations. Climate change and intensification of agriculture have increased nitrogen loads in temperate watersheds. In this study, we explore how nitrogen transported by the six largest Arctic rivers has changed over the past two decades and explore potential climate drivers. In most rivers, the chemical composition of nitrogen has shifted toward less inorganic nitrogen that easily fuels the microbial drivers of poor water quality to more organic nitrogen that is less bioavailable. We find that the observed shifts in the composition of river nitrogen can be explained by the impacts of climate change on precipitation and temperature via their impacts on river discharge and permafrost free extent.
