Currently, climate change is considered as an important factor affecting nutrient loads introduced through riverine systems into the Baltic Sea. Although the prospect of a large increase in pollution has long seemed very real, it still does not translate into planning of effective remedial actions. One of the factors limiting the development of such activities is the scale of simulations, focusing generally on catchment outlet profiles. To fill this gap and enable a step forward in understanding responses toward future predictions in a higher resolution scale (subcatchment), we assessed nutrient load contribution using calculation profiles localized along a main watercourse and its tributaries. To track spatial and seasonal changes of total nitrogen and phosphorus for the Wełna River (central Poland), we used climate change data and the SWAT model. Having at our disposal a catchment model with a good performance we could follow not only total load changes in particular subcatchments, but also track localization of the pollution sources and their direct impact on load estimations. Our results showed an increase of the loads, especially from the agricultural land use type, up to 34% for TN and 85% for TP, in the most extreme scenario. Moreover, forest areas have been noted as highly reactive to climate change, and through their localisation are able to distinctly alter nutrient outflow. Finally, the contribution of urban areas should be further investigated since the dynamics of nitrogen and phosphorus release from impervious surfaces is noticeably different here than from the other diffuse sources.

中文翻译：

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气候变化情景下波罗的海地区低地流域养分源贡献的时空变化

目前，气候变化被认为是影响通过河流系统引入波罗的海的养分负荷的重要因素。尽管污染大幅增加的前景长期以来似乎非常现实，但它仍然没有转化为有效补救行动的规划。限制此类活动发展的因素之一是模拟的规模，通常侧重于流域出口剖面。为了填补这一空白并进一步了解对更高分辨率尺度（子流域）未来预测的响应，我们使用沿主要水道及其支流定位的计算剖面评估了养分负荷贡献。为了跟踪 Wełna 河（波兰中部）总氮和总磷的空间和季节变化，我们使用了气候变化数据和 SWAT 模型。有了性能良好的流域模型，我们不仅可以跟踪特定子流域的总负荷变化，还可以跟踪污染源的定位及其对负荷估算的直接影响。我们的结果显示，在最极端的情况下，负荷增加，尤其是农业用地类型的负荷增加，TN 高达 34%，TP 高达 85%。此外，森林地区对气候变化反应强烈，并且通过其定位能够明显改变养分流出。最后，应进一步研究城市地区的贡献，因为不透水表面的氮和磷释放动态与其他扩散源明显不同。