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Freshwater biodiversity is severely threatened, and despite many efforts to halt biodiversity loss the decline continues. Here, we used a transplantation approach to explore whether failure to reverse this trend for freshwater plants reflects that restoration measures applied to streams are inadequate for restoring suitable habitat conditions for plant species in decline.We identified declining species within the plant genus Potamogeton and introduced five of these (Potamogeton compressus L., Potamogeton gramineus L., Potamogeton lucens L., Potamogeton praelongus Wulfen., and Potamogeton pusillus L.) into five restored lowland stream reaches in three different habitat types to examine species establishment and growth.We found that plant establishment varied among streams and species, but we did not see any effect of habitat type within streams on either species growth or survival. Potamogeton compressus and P. pusillus failed to overwinter, while P. gramineus, P. lucens, and P. praelongus were all able to establish viable stands and to overwinter successfully in several of the experimental streams.Our results suggest that suitable habitats are available for declining Potamogeton species in restored stream reaches in Denmark, but their continued growth may be challenged by limited overwintering success. Consequently, we find it likely that dispersal constraints prevent declining Potamogeton species from naturally recolonising restored stream reaches.Understanding the importance of life history traits, such as overwintering and dispersal, can be crucial for the recovery of plant diversity in streams. Here we show that species that survived during winter were those with extensive growth of roots and rhizomes making them more adapted to withstand high flows than species relying on seeds and turions for overwintering. The creation of calmer backwater habitats can therefore be crucial when restoring stream reaches since these habitats may facilitate overwintering of species lost from the main channel during winter. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) from water samples is increasingly used to detect the presence and distribution of species in aquatic ecosystems. However, before implementing eDNA in monitoring programmes, various species‐specific sampling or analytical issues remain to be resolved in order to minimize frequencies of false‐positive and ‐negative results. For example, empty shells from freshwater pearl mussels (Margaritifera margaritifera) contain extractable DNA (chemical extraction from ground‐up shells) suggesting a risk of false‐positive samples at stream sites with extinct populations but with empty shell material remaining.The aim of this study was to investigate whether empty and naturally degrading shells from M. margaritifera can cause false‐positive eDNA signals in water samples.Water samples were collected from outdoor stream channels (in Lemming, Denmark) with living freshwater pearl mussels or empty shell material (density ~10 individuals m−2) during a 3‐week experimental period. Living freshwater pearl mussels were collected from Hemgravs stream in Sweden and transported to Denmark according to permissions granted by the Swedish and Danish authorities.All water samples from stream channels containing empty shells were negative for eDNA indicating that eDNA traces in stream water are most likely to originate from living individuals located upstream of the sampling site. Water samples collected from stream channels containing living individuals of M. margaritifera were consistently positive for eDNA except for one sample (interpreted as a false negative).The study shows that positive eDNA signals for freshwater pearl mussels most likely reflect the presence of living individuals. Consequently, we suggest that eDNA should be used to locate remaining population fragments of M. margaritifera in deep and turbulent streams, providing a platform for faster and more efficient decision making when launching investigative and mitigation initiatives. [ABSTRACT FROM AUTHOR]