Nitrate isotope database for meteoric waters, surface waters, soil waters, and groundwaters

This data publication includes water chemistry, nitrate isotopic values (δ15N and δ18O), apportioned amounts of unprocessed atmospheric nitrate in freshwaters, streamflow, streamflow apportioned into quick flow, and associated metadata. Data were collected from forested or predominantly forested catchments in the United States and Canada. Some samples were collected for this study or were compiled from published and unpublished studies. The compiled data are from many individual studies on more than 100 catchments measured between 1995 and 2016 from the United States and Canada. The sample types include precipitation (bulk and wet deposition), snow, snow melt, throughfall, stream water, seep water, spring water, soil water, and groundwater. While the data are freely and publicly available, we urge users to cautiously consider limitations of data. Values in this data publication were measured using several different methods (column, bacterial denitrifier, and chemical denitrifier). The absolute values of δ18O in nitrate from the column method may be inaccurate due to particular methodological steps that were used to prepare and analyze samples prior to 2003. Despite absolute errors, distinct end-members and mixed waters (when all were measured) maintain relative ranges. As such, the data from the column method before 2003 may be interpretable for some studies, while inappropriate for other data analyses and interpretations. After 2003, there was general movement to assess and correct exchange and fractionation via use of a more consistent and expansive suite of reference standards. Plus, the denitrifier methods emerged at about that time, and has effectively supplanted use of the column method and led to improved accuracy and precision in nitrate isotope studies. Future contributions of data are welcome and additional data can be added to this repository via contact with the lead author.We measured water chemistry and isotopic tracers of nitrate sources and reanalyzed data from other studies to determine when, where, and how unprocessed atmospheric nitrate was transported in catchments. We compiled data to create a repository for nitrate isotope data from freshwaters in the USA and Canada.Original metadata date was 02/28/2019. Metadata updated on 04/08/2019 to include information about a newly published article. On 06/24/2019 a few longitude measurements were updated in \Supplements\CatchmentInfo.csv.本数据集包含水化学数据、硝酸盐同位素值（δ¹⁵N与δ¹⁸O）、淡水中原生大气硝酸盐的分配占比、径流量（streamflow）数据、拆分为快速流（quick flow）组分的径流量数据，以及相关元数据（metadata）。数据采集自美国与加拿大的森林或森林主导型流域。部分样本为本研究专属采集，其余则整合自已发表及未发表的相关研究。本次整合的数据来自美国与加拿大境内1995至2016年间开展的多项独立研究，覆盖100余个流域。样本类型涵盖降水（总沉降与湿沉降）、积雪、融雪、穿透水（throughfall）、河流水、渗流水、泉水、土壤水与地下水。尽管本数据集可免费公开获取，但我们提请使用者审慎考量数据的局限性。本数据集的相关指标采用多种方法测定，包括柱法、细菌反硝化法与化学反硝化法。2003年以前，由于样品前处理与分析环节采用的特定实验步骤，柱法测定的硝酸盐δ¹⁸O绝对值可能存在误差。尽管存在绝对数值偏差，但明确的端元组分与混合水体（完成全项测定的情况下）仍可保持相对的数值区间。因此，2003年之前的柱法数据可适用于部分研究场景，但不适用于其他数据分析与解读工作。2003年后，学界普遍采用更为统一且覆盖范围更广的参考标准集，以评估并校正同位素交换与分馏效应。与此同时，反硝化法在同期问世，有效替代了柱法的使用，显著提升了硝酸盐同位素研究的准确度与精密度。本数据集欢迎后续数据补充，使用者可通过联系主要作者（lead author）将新增数据纳入本数据库。本团队通过测定水化学指标与硝酸盐来源的同位素示踪剂，并重新分析其他研究的数据，以明确原生大气硝酸盐在流域中的运移时间、路径与机制。我们整合各类数据，构建了美国与加拿大淡水硝酸盐同位素数据的共享数据库。元数据初始创建日期为2019年2月28日；2019年4月8日进行首次更新，补充了一篇新发表论文的相关信息。2019年6月24日，对SupplementsCatchmentInfo.csv文件中的部分经度测量值进行了更新。