Evidencing of copper impact on freshwater environments using Myriophyllum alterniflorum: restoration, biomonitoring, management
Résumé
Myriophyllum alterniflorum D.C., an aquatic macrophyte native to north-European stream freshwaters, was found even in polluted environments from the Vienne river and its tributaries which are often loaded with anthropogenic copper in the Limousin region (France). Vitroplants of this species were reintroduced in degraded localities and the restoration was successful as insect larvae's, crawfishes, leeches and moderlieschen alevins were found in reintroduced macrophyte beds. Furthermore, the good in situ acclimation of the M. alterniflorum patches foresaw potential applications of biomonitoring. Indeed, this species is known to be heavy-metal tolerant and it appears as a good candidate to develop new plant biomarker models specific to pollution in stream environments as none were developed until now. Among ten physiological parameters studied during 35 days after in situ reintroduction, the photosynthetic pigments (chlorophylls a and b, and carotenoids) presented an excellent sensitivity to copper contamination. A strong correlation is obtained between pigment contents of M. alterniflorum and the copper water concentration. This allowed the establishment of models to estimate (i) the phytotoxicity of the heavy metal and (ii) the heavy-metal concentration from the pigment data. The accuracy of the models is limited to copper concentrations ranging from 0,07 µg.l-1 to 12,60 µg.l-1 hence offering many opportunities to apply this new method in a large quantity of European polluted stream waters while using expensive and complex analytical methodologies (e.g. ICP-MS). Owning biological and chemical information from this rapid and cost-effective approach, allows to develop environmental health programs to manage the heavy-metal load in stream ecosystems. Moreover, this study is a breakthrough in the biomonitoring of freshwaters as it leads to enhance environmental management program with the development of new biomarkers from freshwater macrophytes.