UMR 7619 Metis (Sorbonne Université-CNRS-EPHE) BP 123, Tour 56-55, Etage 4, 4 Place Jussieu, 75005, Paris, France.
Université Grenoble Alpes, CNRS, IRD, Grenoble INP (Institute of Engineering Univ. Grenoble Alpes), IGE, F-38000, Grenoble, France.
Environ Sci Pollut Res Int. 2018 Apr;25(12):11924-11939. doi: 10.1007/s11356-018-1428-1. Epub 2018 Feb 15.
The Lot river, a major tributary of the downstream Garonne river, the largest river on the Northern side of the Pyrenees Mountains, was intensively studied in the 1970s. A pioneering program called "Lot Rivière Claire" provided a diagnosis of water quality at the scale of the whole watershed and proposed an ambitious program to manage nutrient pollution and eutrophication largely caused by urban wastewater releases. Later on, the implementation of European directives from 1991 to 2000 resulted in the nearly complete treatment of point sources of pollution in spite of a doubling of the basin's population. At the outlet of the Lot river, ammonium and phosphate contamination which respectively peaked to 1 mg N-NH L and 0.3 mg P-PO L in the 1980s returned to much lower levels in recent years (0.06 mg N-NH L and 0.02 mg P-PO L), a reduction by a factor 15. However, during this time, nitrate contamination has regularly increased since the 1980s, from 0.5 to 1.2 mg N-NO L in average, owing to the intensification of agriculture and livestock farming. Application of the Riverstrahler model allowed us to simulate the water quality of the Lot drainage network for the 2002-2014 period. We showed that, with respect to algal requirements, phosphorus and silica are well balanced, but nitrogen remains largely in excess over phosphorus and silica. This imbalance can be problematic for the ecological status of the water bodies. Using the model, for simulating various scenarios of watershed management, we showed that improvement of urban wastewater treatment would not result in any significant change in the river's water quality. Even though arable land occupies a rather limited fraction of the watershed area, only the adoption of better farming practices or more radical changes in the agro-food system could reverse the trend of increasing nitrate contamination.
洛特河是加龙河下游的一条主要支流，也是比利牛斯山脉北坡最大的河流，在 20 世纪 70 年代得到了深入研究。一个名为“洛特清洁河流”的开创性计划对整个流域的水质进行了诊断，并提出了一项雄心勃勃的计划，旨在主要通过管理城市废水排放来治理营养物污染和富营养化。后来，1991 年至 2000 年期间实施了欧洲指令，尽管流域人口增加了一倍，但基本上已完成了点源污染的处理。在洛特河的出口处，氨氮和磷酸盐污染分别在 20 世纪 80 年代达到峰值，浓度分别为 1mg N-NH₄⁺/L 和 0.3mg P-PO₄³⁻/L，近年来已降至较低水平（分别为 0.06mg N-NH₄⁺/L 和 0.02mg P-PO₄³⁻/L），减少了 15 倍。然而，自 20 世纪 80 年代以来，硝酸盐污染由于农业和畜牧业的集约化而定期增加，平均值从 0.5mg N-NO₃⁻/L 增加到 1.2mg N-NO₃⁻/L。应用河流斯特拉勒模型，我们可以模拟 2002-2014 年洛特河排水网络的水质。结果表明，就藻类需求而言，磷和硅是平衡的，但氮仍然大大超过磷和硅。这种不平衡可能会对水体的生态状况造成问题。通过该模型，我们模拟了各种流域管理情景，结果表明，改善城市废水处理不会对河流水质产生任何显著变化。尽管耕地仅占流域面积的一小部分，但只有采取更好的农业实践或更激进的农业食品系统变革，才能扭转硝酸盐污染增加的趋势。
