The input of nitrogen (N) and phosphorus (P) into rivers has been reduced in recent decades in many regions of the world to mitigate adverse eutrophication effects. However, legislation focused first on the reduction of nutrient loads from point sources and only later on diffuse sources. These reduction strategies have implications on riverine N:P stoichiometry, which potentially alter patterns of algal nutrient limitation and the functions or community structure of aquatic ecosystems. Here, we use a dataset spanning four decades of water quality for the Ruhr River (Germany) to show that the asynchronous implementation of point- and diffuse-source mitigation measures combined with time lags of catchment transport processes caused a temporally asynchronous reduction in dissolved inorganic nitrogen (DIN) and total phosphorus (TP) concentrations. This asynchronous reduction increased the molar N:P ratios from around 30 to 100 in the river sections dominated by point sources, reducing the probability of nitrogen limitation of algae in favor of phosphorus limitation. The Ruhr River catchment and the environmental policies implemented here illustrate the unintended effects of nutrient-control strategies on the ecological stoichiometry at the catchment scale. We urge to assess systematically, whether unintentionally warped macronutrient ratios are observable in other managed river systems and to evaluate their environmental impacts.

中文翻译：

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点源和扩散源的控制异步降低了河流养分浓度，从而扭曲了摩尔 N:P 比率

近几十年来，世界许多地区减少了向河流中输入的氮 (N) 和磷 (P)，以减轻不利的富营养化影响。然而，立法首先侧重于减少点源的营养负荷，后来才侧重于扩散源。这些减少策略对河流 N:P 化学计量有影响，这可能会改变藻类营养限制的模式以及水生生态系统的功能或群落结构。在这里，我们使用跨越鲁尔河（德国）四个十年水质的数据集来表明，点源和扩散源缓解措施的异步实施与集水区运输过程的时间滞后相结合导致溶解无机物的时间异步减少氮 (DIN) 和总磷 (TP) 浓度。这种异步减少使点源主导的河流断面的 N:P 摩尔比从大约 30 增加到 100，降低了藻类氮限制的可能性，有利于磷限制。鲁尔河流域和这里实施的环境政策说明了养分控制策略对流域尺度生态化学计量的意外影响。我们敦促系统地评估在其他受管理的河流系统中是否可以观察到无意扭曲的常量营养素比率，并评估它们的环境影响。鲁尔河流域和这里实施的环境政策说明了养分控制策略对流域尺度生态化学计量的意外影响。我们敦促系统地评估在其他受管理的河流系统中是否可以观察到无意扭曲的常量营养素比率，并评估它们的环境影响。鲁尔河流域和这里实施的环境政策说明了养分控制策略对流域尺度生态化学计量的意外影响。我们敦促系统地评估在其他受管理的河流系统中是否可以观察到无意扭曲的常量营养素比率，并评估它们的环境影响。