Recent trends in the chemistry of major northern rivers signal widespread Arctic change

Rivers integrate processes occurring throughout their watersheds and are therefore sentinels of change across broad spatial scales. River chemistry also regulates ecosystem function across Earth's land-ocean continuum, exerting control from the micro- (for example, local food web) to the macro- (for example, global carbon cycle) scale. In the rapidly warming Arctic, a wide range of processes-from permafrost thaw to biological uptake and transformation-might reasonably alter river water chemistry. Here we use data from major rivers that collectively drain two-thirds of the Arctic Ocean watershed to assess widespread change in biogeochemical function within the pan-Arctic basin from 2003 to 2019. While the oceanward flux of alkalinity and associated ions increased markedly over this time frame, nitrate and other inorganic nutrient fluxes declined. Fluxes of dissolved organic carbon showed no overall trend. This divergence in response indicates the perturbation of multiple processes on land, with implications for biogeochemical cycling in the coastal ocean. We anticipate that these findings will facilitate refinement of conceptual and numerical models of current and future functioning of Arctic coastal ecosystems and spur research on scale-dependent change across the river-integrated Arctic domain. Divergent trends in biogeochemical constituents of the six largest rivers in the Arctic from 2003 to 2019 support multi-faceted changes on the Arctic landscape under global environmental change.

Automated summary

Rivers are sensitive indicators of watershed changes and regulate ecosystem function across the land-ocean continuum. A study on major Arctic rivers found that alkalinity and associated ion fluxes to the ocean increased significantly, while nitrate and other inorganic nutrient fluxes declined. Dissolved organic carbon fluxes showed no overall trend. This indicates disturbance of multiple land processes, with implications for coastal ocean biogeochemical cycling.