ABSTRACT The Rhône River originates in the high Alps and drains an intensely cultivated and industrialised catchment before it discharges to the Gulf of Lion. We investigated the interaction of catchment geomorphology with nitrate sources (atmosphere, agriculture, and nitrification of soil organic matter) and removal processes in large and diverse watersheds on the basis of dual nitrate isotope signatures in river water. In March 2015, we took surface water samples along the Rhône River, including its main tributaries, and measured nutrient concentrations and the stable isotopic composition of nitrate (δ15N, δ18O and Δ17O), and water (δ18O-H2O). Results show that high altitude regions are dominated by nitrate from nitrification in pristine soils and atmospheric deposition, while nitrate in the downstream Rhône River originates mainly from nitrification of agricultural/urban sources. Parallel increases in δ15N and δ18O reflect the influence of primary production. Previous studies suggested robust correlations between land use and . Based on our observation that nitrate δ15N values at higher altitudes are lower than expected, we assume that lower nitrate δ15N values likely reflect limited nitrate consumption and lower soil nitrogen turnover rates. We propose that correlation between land use and nitrate δ15N is sensitive to slope and geomorphology.

中文翻译：

---

硝酸盐来源和土地覆盖对罗纳河集水区硝酸盐同位素组成的影响

摘要 罗纳河发源于阿尔卑斯山，在排入狮子湾之前，流经一个密集耕作和工业化的集水区。我们根据河水中的双重硝酸盐同位素特征，研究了流域地貌与硝酸盐来源（大气、农业和土壤有机质的硝化作用）的相互作用以及大型多样流域的去除过程。2015 年 3 月，我们沿罗纳河（包括其主要支流）采集了地表水样本，并测量了营养盐浓度和硝酸盐（δ15N、δ18O 和 Δ17O）和水（δ18O-H2O）的稳定同位素组成。结果表明，高海拔地区以原始土壤硝化作用和大气沉降产生的硝酸盐为主，而下游罗纳河的硝酸盐主要来自农业/城市来源的硝化作用。δ15N 和 δ18O 的平行增加反映了初级生产的影响。以前的研究表明土地利用和 . 基于我们观察到较高海拔的硝酸盐 δ15N 值低于预期，我们假设较低的硝酸盐 δ15N 值可能反映了有限的硝酸盐消耗和较低的土壤氮周转率。我们提出土地利用与硝酸盐 δ15N 之间的相关性对坡度和地貌敏感。基于我们观察到较高海拔的硝酸盐 δ15N 值低于预期，我们假设较低的硝酸盐 δ15N 值可能反映了有限的硝酸盐消耗和较低的土壤氮周转率。我们提出土地利用与硝酸盐 δ15N 之间的相关性对坡度和地貌敏感。基于我们观察到较高海拔的硝酸盐 δ15N 值低于预期，我们假设较低的硝酸盐 δ15N 值可能反映了有限的硝酸盐消耗和较低的土壤氮周转率。我们提出土地利用与硝酸盐 δ15N 之间的相关性对坡度和地貌敏感。