The Influence of Glacial Cover on Riverine Silicon and Iron Exports in Chilean Patagonia.

Helena V Pryer,Jemma L Wadham,Laura F Robinson,Jade E Hatton,Matthew G Marshall,Sebastien Bertrand,Vreni Häussermann,Richard A Brooker,Beatriz Gill‐Olivas,Giovanni Daneri,Katharine R Hendry,Anne M Kellerman,Jon R Hawkings

doi:10.1029/2020gb006611

Abstract

Glaciated environments have been highlighted as important sources of bioavailable nutrients, with inputs of glacial meltwater potentially influencing productivity in downstream ecosystems. However, it is currently unclear how riverine nutrient concentrations vary across a spectrum of glacial cover, making it challenging to accurately predict how terrestrial fluxes will change with continued glacial retreat. Using 40 rivers in Chilean Patagonia as a unique natural laboratory, we investigate how glacial cover affects riverine Si and Fe concentrations, and infer how exports of these bioessential nutrients may change in the future. Dissolved Si (as silicic acid) and soluble Fe (0.02 m) concentrations were relatively low in glacier‐fed rivers, whereas concentrations of colloidal‐nanoparticulate (0.02–0.45 m) Si and Fe increased significantly as a function of glacial cover. These colloidal‐nanoparticulate phases were predominately composed of aluminosilicates and Fe‐oxyhydroxides, highlighting the need for size‐fractionated analyses and further research to quantify the lability of colloidal‐nanoparticulate species. We also demonstrate the importance of reactive particulate (0.45 m) phases of both Si and Fe, which are not typically accounted for in terrestrial nutrient budgets but can dominate riverine exports. Dissolved Si and soluble Fe yield estimates showed no trend with glacial cover, suggesting no significant change in total exports with continued glacial retreat. However, yields of colloidal‐nanoparticulate and reactive sediment‐bound Si and Fe were an order of magnitude greater in highly glaciated catchments and showed significant positive correlations with glacial cover. As such, regional‐scale exports of these phases are likely to decrease as glacial cover disappears across Chilean Patagonia, with potential implications for downstream ecosystems.

Highlights

One of the most visible effects of climate change is melting of the Earth's cryosphere, with the majority of glaciers currently losing mass at increasingly rapid rates (Zemp et al, 2019)
Despite decreasing riverine concentrations of Colloidal-nanoparticulate size Si (CNSi) and amorphous Si (ASi) with lower glacial cover in Patagonia, dissolved silicon (DSi) concentrations increase with decreasing glacial cover and dominate the Si budget in non-glacial rivers (Figure 2f). Assuming that these relationships hold into the future, our findings suggest that total Si concentrations (DSi + CNSi + ASi) are likely to increase with future glacial retreat
Concentrations of dissolved, colloidal-nanoparticulate, and reactive suspended particulate material (SPM) bound Si and Fe were measured in 40 river systems in Chilean Patagonia

Summary

Introduction

One of the most visible effects of climate change is melting of the Earth's cryosphere, with the majority of glaciers currently losing mass at increasingly rapid rates (Zemp et al, 2019). The implications of enhanced glacial retreat on biogeochemical cycles are still not well understood, despite potentially critical impacts for coastal ecosystems, the carbon cycle, and global climate (Wadham et al, 2019). Glacial systems have been highlighted as natural factories for lithogenic nutrients, with meltwaters potentially sustaining productivity in downstream ecosystems (Hawkings et al, 2014, 2015; Wadham et al, 2019)

Methods

Results

Discussion

Conclusion