Nitrogen pollution negatively affects Stratiotes aloides in Central-Eastern Europe. Implications for translocation actions

1. The preliminary evaluation of threats and the possibility of their removal or mitigation is a key issue for a successful translocation. Here, the possibility to reintroduce Stratiotes aloides in Italy where it had become extinct about 25 years ago was investigated by studying the difference in water quality in sites where the species currently exists in Europe, where the species has recently disappeared (extinct) and in proposed translocation sites. 2. Sediment pore-water samples and surface water samples were collected in 18 localities in The Netherlands, Germany, Hungary, Italy and Romania, representing six European river basins. 3. The high concentrations of surface water inorganic nitrogen (especially nitrates) were identified as the likely cause of decline of S. aloides in central-eastern Europe and the cause of extinction of the species in Italy. 4. The proposed translocation sites are more similar to current conditions of extinct sites than current sites of occurrence of S. aloides, affecting the possibility of successfully reintroducing the species at the southern edge of its European range. Increasing concentration of nitrates in other parts of the species range might further decrease the species abundance.