Université Grenoble Alpes, CNRS , IRD, Grenoble INP, Institut des Géosciences de l'Environnement, IGE , 38000 , Grenoble , France.
Université Grenoble Alpes, CNRS , Laboratoire d'Ecologie Alpine, LECA , 38000 , Grenoble , France.
Environ Sci Technol. 2018 May 15;52(10):5561-5570. doi: 10.1021/acs.est.7b02395. Epub 2018 Apr 30.
Nitrogen is an essential nutrient for life on Earth, but in excess, it can lead to environmental issues (e.g., N saturation, loss of biodiversity, acidification of lakes, etc.). Understanding the nitrogen budget (i.e., inputs and outputs) is essential to evaluate the prospective decay of the ecosystem services (e.g., freshwater quality, erosion control, loss of high patrimonial-value plant species, etc.) that subalpine headwater catchments provide, especially as these ecosystems experience high atmospheric nitrogen deposition. Here, we use a multi-isotopic tracer (ΔO, δN and δO) of nitrate in aerosols, snow, and streams to assess the fate of atmospherically deposited nitrate in the subalpine watershed of the Lautaret Pass (French Alps). We show that atmospheric N deposition contributes significantly to stream nitrate pool year-round, either by direct inputs (up to 35%) or by in situ nitrification of atmospheric ammonium (up to 35%). Snowmelt in particular leads to high exports of atmospheric nitrate, most likely fast enough to impede assimilation by surrounding ecosystems. Yet, in a context of climate change, with shorter snow seasons, and increasing nitrogen emissions, our results hint at possibly stronger ecological consequences of nitrogen atmospheric deposition in the close future.
氮是地球上生命的必需养分，但过量的氮会导致环境问题（例如氮饱和、生物多样性丧失、湖泊酸化等）。了解氮收支（即输入和输出）对于评估亚高山集水区提供的生态系统服务（例如淡水质量、侵蚀控制、高遗产价值植物物种丧失等）的潜在衰减至关重要，特别是因为这些生态系统经历了较高的大气氮沉积。在这里，我们使用气溶胶、雪和溪流中硝酸盐的多同位素示踪剂（ΔO、δN 和 δO）来评估法国阿尔卑斯山劳特雷特山口（Lautaret Pass）亚高山流域中大气硝酸盐的归宿。我们表明，大气氮沉积全年通过直接输入（高达 35%）或大气氨的原位硝化（高达 35%）对溪流硝酸盐库有显著贡献。特别是融雪导致大气硝酸盐的大量输出，这很可能快到足以阻止周围生态系统的吸收。然而，在气候变化的背景下，雪季缩短，氮排放量增加，我们的结果表明，在不久的将来，大气氮沉积可能会对生态系统产生更强的影响。
