Reproduction of Crassula helmsii by seed in western Europe

The amphibious plant species Crassula helmsii is a widely established and still-spreading alien in various parts of Europe, where it is considered invasive as its dense swards stress the viability of local biota. The species was considered to exclusively reproduce through vegetative means, until ex situ germination was recorded from a single locality in Belgium. We assessed whether this seed viability holds on a wider scale, by testing 16 populations from The Netherlands, Belgium, northern France, eastern England and northern Germany in a greenhouse germination experiment. Seedlings were observed from all populations but two, and from each of the five countries. Although most fruits were lacking seeds and the inferred germination percentages were overall low, germinable seed numbers are considerable given the high density of flowering stems. An in situ test revealed seeds to make it through normal winter conditions without signs of physical damage and with retention of germinability. Our results suggest that reproduction by seed is a relatively cryptic but widespread phenomenon throughout western Europe. The persistency of seed banks requires further investigation. Nonetheless, these findings already challenge the efficacy of techniques currently applied in C. helmsii control

Exposition des enfants par ingestion de sol et de poussières contaminés : quels choix pour les évaluations de risque ?

National audienceEn Evaluation Quantitative des Risques Sanitaires (EQRS), l'ingestion de sol est une voie d'exposition influente dans le calcul de la prédiction des expositions des populations. Le potentiel d'exposition aux polluants du sol est plus grand pour les enfants que les adultes, en raison notamment de comportements très différents, lors d'activités de jeu par exemple. Cette voie d'exposition est conditionnée par deux paramètres sensibles : la quantité de terre ingérée et la biodisponibilité pour l'homme du composé chimique à partir de la matrice sol. Ce dernier paramètre qui caractérise la fraction absorbée d'un polluant peut être approché par la bioaccessibilité (fraction dissoute du contaminant dans le tube digestif). Actuellement il est considéré qu'un enfant ingère entre 100 et 150 mg/j de terre et que la biodiponibilité d'un élément dans cette terre est totale.L'analyse des connaissances scientifiques disponibles a eu pour objectifs d'être à même de justifier d'éventuelles propositions : fixer une valeur ou une distribution de quantité de sol et de poussières ingérée pour l'enfant (hors pica et géophagie) ; examiner la façon dont les notions de biodisponibilité/bioaccessibilité des polluants dans le sol et les poussières ingérés pouvaient être intégrées dans les pratiques d'évaluation de risque

Een dijk en een woonplatform uit de Romeinse periode in Stene (Oostende)

De opgravingen in Stene behoren tot een van de weinige archeologische operaties in de Vlaamse kustvlakte waarbij bewoningssporen uit de Romeinse periode in situ onderzocht zijn. Bovendien werd hier een nieuw inzicht verkregen in de bewoningsstructuur en de manier waarop de mens het dynamische kustlandschap naar zijn hand probeerde te zetten. Waarschijnlijk kende de vindplaats vóór de aanleg van de dijk een volledig zout milieu waarbij zeewater tweemaal per dag werd aangevoerd via een systeem van getijdengeulen. Bedijking was dus nodig om een zone aan de invloed van het water te onttrekken. Enige tijd later bouwde men tegen deze dijk een woonplatform aan dat in meerdere fasen is opgeworpen en dat minstens twee bewoningsfasen heeft gekend. Vondsten wijzen erop dat het gebied gericht was op veeteelt en akkerbouw. Het is duidelijk dat menselijke ingrepen en activiteiten in de kustvlakte significanter waren dan tot nog toe gedacht, in elk geval in de Romeinse periode en misschien ook vroeger. Dit onderzoek zet aan om met andere ogen en met behulp van een andere methodiek toekomstig onderzoek in de kustvlakte aan te pakken en deze site te beschouwen als een eerste stap naar nieuwe inzichten in het complexe kustcultuurlandschap

Cabomba caroliniana Gray (Cabombaceae) invades major waterways in Belgium

Recently, unattached viable stem fragments of the invasive macrophyte Cabomba caroliniana Gray were found at several locations in two canals in northern Belgium. A subsequent survey of the canal Zuid-Willemsvaart revealed one site with rooted plants and the presence of floating stem fragments along the entire length of the canal (25 km). These findings indicate that C. caroliniana is already well established in the Zuid-Willemsvaart and probably considerably more widespread than previous records from isolated lentic water bodies indicate. We have summarised the new records and discuss the potential spread and risks associated with further establishment and spread of C. caroliniana in Belgium

Macrophyte assessment in European lakes: Diverse approaches but convergent views of 'good' ecological status

The European Water Framework Directive has been adopted by Member States to assess and manage the ecological integrity of surface waters. Specific challenges include harmonizing diverse assessment systems across Europe, linking ecological assessment to restoration measures and reaching a common view on ‘good’ ecological status. In this study, nine national macrophyte-based approaches for assessing ecological status were compared and harmonized, using a large dataset of 539 European lakes. A macrophyte common metric, representing the average standardized view of each lake by all countries, was used to compare national methods. This was also shown to reflect the total phosphorus (r2 = 0.32), total nitrogen (r2 = 0.22) as well as chlorophyll-a (r2 = 0.35–0.38) gradients, providing a link between ecological data, stressors and management decisions. Despite differing assessment approaches and initial differences in classification, a consensus was reached on how type-specific macrophyte assemblages change across the ecological status gradient and where ecological status boundaries should lie. A marked decline in submerged vegetation, especially Charophyta (characterizing ‘good’ status), and an increase in abundance of free-floating plants (characterizing ‘less than good’ status) were the most significant changes along the ecological status gradient. Macrophyte communities of ‘good’ status lakes were diverse with many charophytes and several Potamogeton species. A large number of taxa occurred across the entire gradient, but only a minority dominated at ‘less than good’ status, including filamentous algae, lemnids, nymphaeids, and several elodeids (e.g., Zannichellia palustris and Elodea nuttallii). Our findings establish a ‘guiding image’ of the macrophyte community at ‘good’ ecological status in hard-water lakes of the Central-Baltic region of Europe

Redundancy in the ecological assessment of lakes: Are phytoplankton, macrophytes and phytobenthos all necessary?

Although the Water Framework Directive specifies that macrophytes and phytobenthos should be used for the ecological assessment of lakes and rivers, practice varies widely throughout the EU. Most countries have separate methods for macrophytes and phytobenthos in rivers; however, the situation is very different for lakes. Here, 16 countries do not have dedicated phytobenthos methods, some include filamentous algae within macrophyte survey methods whilst others use diatoms as proxies for phytobenthos. The most widely-cited justification for not having a dedicated phytobenthos method is redundancy, i.e. that macrophyte and phytoplankton assessments alone are sufficient to detect nutrient impacts. Evidence from those European Union Member States that have dedicated phytobenthos methods supports this for high level overviews of lake condition and classification; however, there are a number of situations where phytobenthos may contribute valuable information for the management of lakes