Nitrogen pollution is one of the main problems affecting the environment and human activity. This is especially true in semiarid regions where the quantity-quality relationship is a key constraining factor. In this paper, we propose and apply a method to quantify the economic value of the environmental service a river provides as a nitrate purifier/diluent. The main aim is to provide water management decisions with a solid and easily replicable method. Specifically, this study proposes a method to assess two processes of the water quality regulation service, namely, nitrate removal and dilution, through avoided decontamination costs. The proposed method is applied in the Ebro river basin as a role model. This application allows us to define the concepts in an operational manner. Since water availability forecasts are a key factor, we explore and analyze our results in accordance with several climate-change scenarios. The results show that the economic value of the removal service at the watershed scale amounts to about €92.3 million per year. Estimates of the annual economic value of the dilution service in the whole basin range more largely from €21.8 to €111.7 million, depending on the climate change scenario considered. To our knowledge, this is the first time that the dilution and removal services provided by rivers are jointly assessed.

氮污染是影响环境和人类活动的主要问题之一。在数量-质量关系是关键约束因素的半干旱地区尤其如此。在本文中，我们提出并应用一种方法来量化河流作为硝酸盐净化器/稀释剂所提供的环境服务的经济价值。主要目的是通过可靠且易于复制的方法来提供水管理决策。具体而言，本研究提出了一种通过避免去污成本来评估水质调节服务的两个过程（即硝酸盐去除和稀释）的方法。所提出的方法在埃布罗河流域作为榜样被应用。该应用程序允许我们以操作方式定义概念。由于水供应量预测是关键因素，我们根据几种气候变化情景探索和分析我们的结果。结果表明，分水岭地区拆除服务的经济价值每年约为9,230万欧元。根据所考虑的气候变化情景，整个流域稀释服务的年度经济价值估计范围从21.8欧元到1.117亿欧元不等。据我们所知，这是首次对河流提供的稀释和去除服务进行联合评估。取决于所考虑的气候变化方案。据我们所知，这是首次对河流提供的稀释和去除服务进行联合评估。取决于所考虑的气候变化方案。据我们所知，这是首次对河流提供的稀释和去除服务进行联合评估。