Long‐Term Changes in Concentration and Yield of Riverine Dissolved Silicon From the Poles to the Tropics

Abstract

Riverine exports of silicon (Si) influence global carbon cycling through the growth of marine diatoms, which account for ∼25% of global primary production. Climate change will likely alter river Si exports in biome‐specific ways due to interacting shifts in chemical weathering rates, hydrologic connectivity, and metabolic processes in aquatic and terrestrial systems. Nonetheless, factors driving long‐term changes in Si exports remain unexplored at local, regional, and global scales. We evaluated how concentrations and yields of dissolved Si (DSi) changed over the last several decades of rapid climate warming using long‐term datasets from 60 rivers and streams spanning the globe (e.g., Antarctic, tropical, temperate, boreal, alpine, Arctic systems). We show that widespread changes in river DSi concentration and yield have occurred, with the most substantial shifts occurring in alpine and polar regions. The magnitude and direction of trends varied within and among biomes, were most strongly associated with differences in land cover, and were often independent of changes in river discharge. These findings indicate that there are likely diverse mechanisms driving change in river Si biogeochemistry that span the land‐water interface, which may include glacial melt, changes in terrestrial vegetation, and river productivity. Finally, trends were often stronger in months outside of the growing season, particularly in temperate and boreal systems, demonstrating a potentially important role of shifting seasonality for the flux of Si from rivers. Our results have implications for the timing and magnitude of silica processing in rivers and its delivery to global oceans.

Drifting along: using diatoms to track the contribution of microbial mats to particulate organic matter transport in a glacial meltwater stream in the McMurdo Dry Valleys, Antarctica

“…In addition, the weathering of this biogenic silica in the hyporheic zone may contribute to dissolved silicon in the streamwater, as indicated by the analysis of silicon isotopes by Hirst et al (2020) and Hatton et al (2020) . Taken as a whole, these findings suggest that silicon transport in these streams may be influenced by autochthonous biological processes in the stream and its hyporheic zone to a much greater extent than in streams and rivers in other regions where allochthonous watershed biogeochemical processes are dominant ( Jankowski et al, 2023 ).…”

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.…”

Establishing fluvial silicon regimes and their stability across the Northern Hemisphere

“…Shifts in Si concentrations with respect to other nutrients (i.e., nitrogen and phosphorus) may facilitate preferential growth of potentially harmful, non-silicious algae, with effects on water quality and ecosystem health (Conley et al 1993;Turner et al 2003). A recent synthesis of long-term trends in fluvial Si concentrations and loads from 60 streams showed that Si concentrations were changing, and that the timing of change during the year varied across and within biomes (Jankowski et al 2023), indicating widespread changes in Si watershed processing may be occuring.…”