Pryer Helena V, Hawkings Jon R, Wadham Jemma L, Robinson Laura F, Hendry Katharine R, Hatton Jade E, Kellerman Anne M, Bertrand Sebastien, Gill-Olivas Beatriz, Marshall Matthew G, Brooker Richard A, Daneri Giovanni, Häussermann Vreni
Bristol Glaciology Centre, Department of Geographical Sciences University of Bristol Bristol UK.
School of Earth Sciences University of Bristol Bristol UK.
Global Biogeochem Cycles. 2020 Dec;34(12):e2020GB006611. doi: 10.1029/2020GB006611. Epub 2020 Dec 17.
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 μm) concentrations were relatively low in glacier-fed rivers, whereas concentrations of colloidal-nanoparticulate (0.02-0.45 μm) 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 μm) 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.
冰川环境已被视为生物可利用养分的重要来源，冰川融水的输入可能会影响下游生态系统的生产力。然而，目前尚不清楚河流养分浓度如何随冰川覆盖范围的变化而变化，这使得准确预测随着冰川持续消退陆地通量将如何变化具有挑战性。我们以智利巴塔哥尼亚的40条河流作为一个独特的天然实验室，研究冰川覆盖如何影响河流中的硅和铁浓度，并推断这些生物必需养分的输出在未来可能会如何变化。在冰川补给的河流中，溶解态硅（以硅酸形式存在）和可溶性铁（<0.02μm）的浓度相对较低，而胶体 - 纳米颗粒态（0.02 - 0.45μm）的硅和铁浓度则随着冰川覆盖范围的增加而显著增加。这些胶体 - 纳米颗粒相主要由铝硅酸盐和铁的氢氧化物组成，这突出了进行粒径分级分析以及进一步研究以量化胶体 - 纳米颗粒物种活性的必要性。我们还证明了硅和铁的活性颗粒态（>0.45μm）相的重要性，这些相在陆地养分预算中通常未被考虑，但可能在河流输出中占主导地位。溶解态硅和可溶性铁的输出量估计值未显示出随冰川覆盖范围的变化趋势，这表明随着冰川持续消退，总输出量没有显著变化。然而，在冰川覆盖度高的集水区，胶体 - 纳米颗粒态和与沉积物结合的活性硅和铁的输出量要高出一个数量级，并且与冰川覆盖范围呈现出显著的正相关。因此，随着智利巴塔哥尼亚地区冰川覆盖消失，这些相的区域尺度输出量可能会减少，这可能会对下游生态系统产生影响。
