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

Abstract

Large rivers integrate processes occurring throughout their watersheds, and are therefore sentinels of change across broad spatial scales. Riverine chemistry also regulates ecosystem function across Earth's land-ocean continuum, exerting control from the micro-(e.g., food web) to the macro-(e.g., carbon cycle) scale. In the rapidly warming Arctic, a wide range of processes have been hypothesized to alter river water chemistry. However, it is unknown how the land-ocean flux of waterborne constituents is changing at the pan-Arctic scale. Here, we show profound shifts in the concentration and transport of biogeochemical constituents in the six largest Arctic rivers (the Ob', Yenisey, Lena, Kolyma, Yukon, and Mackenzie) since 2003, near river mouths capturing two-thirds of the pan-Arctic watershed. While some constituent fluxes increase substantially at the pan-Arctic scale (alkalinity and associated ions), others decline (nitrate and associated inorganic nutrients) or are overall unchanged (dissolved organics). These clear but divergent trends diagnose a multi-systems perturbation that indicates alteration of processes ranging from chemical weathering on land, to primary production in the coastal ocean. We anticipate these findings will refine models of current and future functioning of the coupled land-ocean Arctic system, and spur research on scale-dependent change across the riverintegrated Arctic domain. MainLarge rivers are planetary linchpins, connecting vast swaths of terrestrial landmass to the world's coastal oceans. On land, rivers integrate patchy landscapes and the variable biogeochemical processes that these landscapes host, as water moving through watersheds incorporates the chemical signature of its flow path. In the coastal ocean, the chemical signature of water transported by rivers regulates nearshore biogeochemical 1,2 and ecological 3,4 function; over broader scales, river water and its composition modify ocean physics 1 . Nowhere is this more consequential than in the Arctic, where ~11% of Earth's riverine discharge drains into an enclosed basin containing ~1% of global ocean volume 5 . This drainage occurs predominantly via six large rivers (Figure 1, Extended Data Table 1). As a result, quantifying trends in river water chemistry at a constrained series of downstream sites allows us to diagnose change across much of the pan-Arctic watershed, better understand the current functioning of the connected land-ocean Arctic system, and predict what the future may hold for this rapidly changing region 6 .

Links Between Stream Water Nitrogen and Terrestrial Vegetation in Northeast Greenland

“…Headwater streams show intimate connectivity to their catchments and are therefore ideal sites for inferring catchments effects on stream water chemistry (Hynes, 1975) or disentangling catchments processes from stream water chemistry Kendrick et al, 2018). Studies on small headwater stream catchments rather than only considering large river catchments (Frey & McClelland, 2009;Tank et al, 2023;Toohey et al, 2016) are essential for enhancing the understanding of the mechanistic links between vegetation, hydrological connectivity, and solute runoff (e.g., Khosh et al, 2017;McNamara et al, 2008;Pastor et al, 2021), that eventually are affecting the larger-scale patterns in solute runoff to rivers and coastal areas. In addition, we conducted the study in NE Greenland, where only two other studies linking catchment characteristics and stream water chemistry exist (Docherty et al, 2018;Pastor et al, 2021).…”

The Role of Coastal Yedoma Deposits and Continental Shelf Sediments in the Arctic Ocean Silicon Cycle

“…Continued, or enhanced Si loading from Yedoma deposit erosion may further enhance the potential for Si burial and recycling in the Arctic Ocean. Changing riverine inputs, considering total discharge, total Si load, and the balance of DSi and ASi (Carey et al, 2020;Frey et al, 2007;Jankowski et al, 2023;Tank et al, 2023) will likely play an important role in regulating future rates of Si burial and recycling on Arctic continental shelves. Beyond the Arctic Ocean, exported Si from the Arctic Ocean fuels one of the most productive regions in the world, the North Atlantic.…”

“…However, the Arctic Ocean is changing rapidly, particularly in the shallow shelf areas due to climate change with warmer waters, less ice, increased primary production, and accelerating coastal erosion (Gustafsson et al., 2011; Lewis et al., 2020; Meredith et al., 2019; Terhaar et al., 2020; Wild et al., 2019). Further, riverine inputs of Si to the Arctic Ocean may also be changing (Jankowski et al., 2023; Tank et al., 2023). As continental shelf areas make up more than half of the area of the Arctic Ocean (∼53% of the Arctic Ocean; Jakobsson, 2002), understanding the Si cycle in these regions is necessary to project how the Arctic Ocean Si budget might respond to changing ocean and climate conditions.…”

Hydrology Controls Dissolved Organic Carbon and Nitrogen Export and Post‐Storm Recovery in Two Arctic Headwaters

“…Overall, our findings highlight that storm events play an important role in the co‐exports of C and N in intermediate‐scale (<100 km 2 ) Arctic headwaters, which represent a significant source of uncertainty in high‐latitude biogeochemical budgets (Starr et al., 2023). Notably, patterns of non‐changing riverine fluxes of DOC concurrent with declining fluxes of $${{\text{NO}}_{3}}^{-}$$ have emerged at larger watershed scales (>10,000 km 2 ) (Tank et al., 2023), while increasing exports of DON (a large portion of TDN) have significant implications for productivity of the Arctic Ocean (Tank et al., 2012). While changes in fluxes observed at the large catchment scale represent many competing mechanisms that drive the directional shifts in N concentrations, these changes likely start far upstream.…”