We combine historical and recent monitoring data with modeling to get a better insight into water quality development of the large Oder/Szczecin Lagoon at the German/Polish border in the southern Baltic Sea region and especially of the role of macrophytes. Data indicates that the system is eutrophic for centuries and a naturally eutrophic system. During the last decades, external nutrient loads decreased but still keep the system in a eutrophic state. The systems primary production is limited by light and nitrogen and cannot be sufficiently managed by external nutrient load reductions. We consider 36% macrophyte coverage of the lagoon area as potential historical maximum. Despite its shallowness the lagoon was never a macrophyte dominated, clear water system. About 31% of the lagoon area would be covered by macrophytes in a good ecological status according to the European Water Framework Directive. However, the existing water transparency targets seem too ambitious and not realistic. Changes in macrophyte coverage on water quality are restricted to near shore areas and hardly affect the open lagoon. Existing models require an improved representation of water transparency and effects on macrophyte colonization depth. Presently the patchy macrophyte coverage is only about 12% of the lagoon area. This low coverage and a relatively poor species composition results in a non-satisfactory state classification. However, ecologically valuable angiosperms and charophytes seem to recover. A strict avoidance of mechanical disturbances could be a measure to support macrophyte re-colonization. A systematic improvement of piscivorous fish stocks may be a supporting measure to reduce eutrophication. Restoration perspectives and consequences for environmental policies are discussed.

中文翻译：

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大型波罗的海泻湖的水生植物和水质：相关性、发展和恢复前景

我们将历史和最近的监测数据与建模相结合，以更好地了解位于波罗的海南部地区德国/波兰边界的大型奥得河/什切青泻湖的水质发展，尤其是大型植物的作用。数据表明，该系统富营养化了几个世纪，是一个自然富营养化的系统。在过去几十年中，外部养分负荷减少，但仍使系统处于富营养状态。该系统的初级生产受到光和氮的限制，不能通过减少外部养分负荷来充分管理。我们认为泻湖地区 36% 的大型植物覆盖率是潜在的历史最大值。尽管泻湖很浅，但它从来不是以大型植物为主的清澈水系。根据欧洲水框架指令，大约 31% 的泻湖面积将被生态状况良好的大型植物覆盖。然而，现有的水透明度目标似乎过于雄心勃勃且不现实。大型植物覆盖对水质的影响仅限于近岸地区，几乎不会影响开阔的泻湖。现有模型需要改进水透明度和对大型植物定植深度影响的表示。目前，片状水生植物覆盖率仅为泻湖面积的 12% 左右。这种低覆盖率和相对较差的物种组成导致状态分类不令人满意。然而，具有生态价值的被子植物和轮藻似乎正在恢复。严格避免机械干扰可能是支持大型植物重新定植的一项措施。系统性改善食鱼鱼类种群可能是减少富营养化的辅助措施。讨论了环境政策的恢复观点和后果。