Crested floating heart [Nymphoides cristata (Roxb.) Kuntze] is an invasive aquatic plant in the southeastern United States. For clonal plants like N. cristata, clonal diversity may influence response to control tactics and/or evolutionary potential. However, little is known about the diversity of introduced N. cristata. In this study, we used genotyping-by-sequencing to quantify N. cristata diversity in the southeastern U.S. and determine how that diversity is distributed across the invaded range. Our results show that at least three distinct genetic lineages of N. cristata are present in the southeastern U.S. Geographic distribution of the lineages varied, with one widespread lineage identified across several states and others only found in a single waterbody. There is also evidence of extensive asexual reproduction, with invaded waterbodies often host to a single genetic lineage. The genetic diversity reported in this study likely results from multiple introductions of N. cristata to the southeastern U.S. and should be considered by managers when assessing control tactics such as screening for biocontrol agents or herbicide testing. The extent and distribution of genetic diversity should also be considered by researchers studying the potential for invasive spread of N. cristata within the U.S. or hybridization with native Nymphoides species.

Eurasian watermilfoil (Myriophyllum spicatum L.) is an aquatic vascular plant that forms extensive dense beds in lakes. This invader competes with native plants, interferes with aquatic activities, and decreases riparian property values. In Canada, the use of aquatic herbicides is highly restricted. Environmental managers must therefore rely on physical methods such as hand pulling or benthic matting for control. Although these methods are not new, there has been little scientific investigation regarding their effectiveness and cost over multiple years. Benthic matting and hand pulling were used in Lac des Abénaquis (area: 1.2 km2) to control 3.6 ha of M. spicatum beds. Initiated by citizens in 2016, control procedures were scientifically studied in 2020 and 2021. Benthic fiberglass mats were deployed on dense M. spicatum patches for 10 wk. Isolated plants and patches <100 m2 were hand pulled by divers, and the harvested material surfaced via a suction hose or in hand-filled bags. By August 2021, all the M. spicatum patches had been eliminated, and only 560 widely scattered plants remained. Over the last 2 yr of control, hand pulling required 243 person-hours and removed 2,245 kg of biomass. The biomass brought to the surface was 2.4 times higher per person-hour with the suction system than with bags. The use of 1,000 m2 of benthic mats required 47 to 51 person-hours per summer season, including installation, removal, and maintenance. Intensive management (years 1 to 5) using benthic mats and hand pulling cost an estimated Can$185,000 (US$140,000) ha−1 of M. spicatum bed. Hand pulling of scattered individuals (years 6+), estimated at Can$20,000 (US$15,000) per summer, is essential to avoid reinfestation. An invasion of M. spicatum can successfully be managed in small lakes without herbicides, but control remains a costly and long-term endeavor.

De 1977 à 2009, plus de 600 analyses d’activités en tritium organique ont été réaliséessur les poissons, les végétaux aquatiques et les sédiments, en amont et en aval des 15CNPE français situés en bord de rivière. L’exploitation de ces résultats montre que lesactivités en tritium organique ont diminué de façon exponentielle au cours des trentedernières années, dans tous les compartiments des écosystèmes aquatiques. Dans les zonesen amont de tout CNPE, les activités en tritium organique dans les sédiments sontsupérieures aux activités mesurées dans les poissons et les végétaux, elles-mêmessupérieures aux activités en HTO des eaux de surface. L’ampleur de ces écarts dépend dubassin concerné et s’explique par la nature différente des sources de tritium. Dans lesbassins versants où les retombées des essais nucléaires atmosphériques constitue la sourceprincipale de tritium, les niveaux observés résultent de l’exposition des organismesaquatiques à deux formes distinctes de tritium d’âges différents : l’eau tritiée del’atmosphère, image des retombées au moment du prélèvement, et le tritium organique dessols, formé sur plusieurs dizaines d’années, qui alimente le compartiment sédimentaire descours d’eau. Dans les bassins du Rhône et du Rhin, une source supplémentaire de tritium detrès faible biodisponibilité, provenant vraisemblablement de l’industrie des peinturesluminescentes, marque la matière organique des sédiments à hauteur de 100 à 100 000Bq.L-1 d’eau de combustion. La comparaison des niveaux observés en amont eten aval des CNPE montre que l’influence des rejets est détectable seulement dans les coursd’eau où le bruit de fond est faible, c’est-à-dire dans les bassins autres que ceux duRhône et du Rhin. L’augmentation des activités en tritium organique dans les végétaux etles poissons est inférieure à l’augmentation de l’activité en HTO due aux rejets, ce quitémoigne, d’une part, de l’absence de phénomène de bioaccumulation à partir de l’eautritiée et, d’autre part, de l’absence de composés organiques bioaccumulables dans lesrejets.

The aim of this work was to evaluate the potential of aquatic macrophytes as biological indicators of the environmental conditionsof rivers in north-eastern Spain. To this end, twenty five river basins were studied to assess the species composition andabundance of macrophytes, and to examine their relation with different geographic, morphometric, mineralization, and trophicstatus parameters. Of the twenty six macrophyte species found, five appeared to be useful as biological indicators of the environmentalconditions of the rivers. L. minor was a good indicator of high mineralization (i.e., conductivity and Cl-) and high trophicstate (especially, N-NO2 -). C. stagnalis was a good indicator of high P-PO4 3- concentrations. P. crispus, P. polygonifolius,and R. penicillatus seemed to be useful indicators of high N-NO3 - concentration. We conclude that, in our study area, aquaticmacrophytes can indeed be used as biological indicators of the environmental conditions of rivers.

The aim of our paper was to study the space and time variations of phosphorus contents in the sediment, water and tissue of aquatic plants. Tissue Total Phosphorus of six aquatic plants (Callitriche platycarpa, C. hamulata, C. obtusangula, Elodea nuttallii, E. canadensis and Ranunculus peltatus) was analysed alongside the sediment Total Phosphorus (TP) and Soluble Reactive Phosphorus concentrations (SRP) in water, at the same site. Twelve sites were selected, and, samples were collected to test the seasonal and the annual patterns of phosphorus variation in 3 compartments. Streams ranged from oligotrophic to eutrophic waters. The sediments varied from mesotrophic to eutrophic states. A highly significant site effect was shown for water and for sediment. Water SRP varied with time (season, year), whereas no significant time effect was established for the sediment TP. Tissue TP varied according to year and season in Callitriche platycarpa, C. hamulata and E. nuttallii. The tissue phosphorus storage depended on the trophic level of sediment and water and varied according to species. The rank order of tissue TP content was C. obtusangula > R. peltatus ≥ E. nuttallii ≥ E. canadensis > C. platycarpa > C. hamulata. Removal of aquatic plants biomass with its accumulated phosphorus could be an alternative technique to other eutrophication control strategies. Further work is needed to improve our knowledge to estimate the ecological risk of harvesting on biodiversity and on ecosystem function.