Aquatic and terrestrial proxy evidence for Middle Pleistocene palaeolake and lake‐shore development at two Lower Palaeolithic sites of Schöningen, Germany

The archaeological sites in the open‐cast mine of Schöningen, Germany, represent outstanding archives for understanding Middle Pleistocene interglacial–glacial transitions and human adaption. Aquatic microfossil and pollen assemblages from the ‘Reinsdorf sequence’, likely correlated to Marine Isotope Stage 9, document environmental changes from a thermal maximum to succeeding glacial conditions recorded in two sequences of excavation sites 12 II and 13 II. Multi‐proxy analyses enable detailed reconstruction of lake‐shore and landscape developments despite variable microfossil preservation in changing carbonate‐ and organic‐rich deposits. Rich aquatic vegetation with abundant charophytes suggests repeated phases with water depths of 0.5–2 m at site 13 II, while even greater temporary depths are deduced for 12 II DB. Mesorheophilic and mesotitanophilic ostracod species indicate stream inflows with medium–low calcium contents of >18 mg Ca L –1 originating from nearby springs. Diatoms point to meso‐eutrophic conditions and an alkaline pH of the lake water. Interglacial conditions with thermophile forests but no aquatic microfossils preserved, suggesting a dry or only temporarily flooded site, mark the beginning of the sequence. Continuous presence of aquatic organisms and overall dominance of small tychoplanktonic diatoms during a subsequent cool steppe phase provide evidence for increased water depths and unstable habitats characterized by erosion and probably prolonged periods of lake ice cover. During the succeeding boreal forest‐steppe phase, surface runoff into the productive, shallow lake decreased due to a more extensive vegetation cover. Concurrently, intensified groundwater input in contact with the nearby salt wall caused elevated salinities. Following a lake level drop, stream inflows and lake levels increased again towards the end of the Reinsdorf sequence and promoted development of a diverse fauna and flora at the lake shore; thereby maintaining an attractive living and hunting environment for early humans during a phase of generally cooler temperatures and landscape instability at the transition into a glacial period

Aproximación a las comunidades de carófitos que existieron en la Albufera de Valencia a partir del estudio de las oósporas del sedimento

Charophyte oospores and their features (size, shape, colour, outer wall ornamentation, etc.) are able to persist in seed banks of aquatic ecosystems. Thus, these characteristics can be used for taxonomic species identification, thereby providing knowledge about the specific composition of the charophyte community in a habitat that currently lacks, or has greatly altered, submerged vegetation. Several years ago, l’Albufera de València lost the charophyte meadows that covered the lake bottom in the past, which had never been studied in detail. Several sediment cores were extracted from the lagoon at three sites and the oospores and gyrogonites were isolated and characterized. The oospore/gyrogonite densities in the sediment layers were estimated. Ten different taxa have been identified: six belonging to genus Chara [Ch. vulgaris, Ch. Hispida var. major, Ch. fragilis (Ch. globularis), Ch. Hispida var. baltica, Ch. aspera, Ch. tomentosa]; one Nitella species (N. hyalina), two Tolypella species (T. glomerata and T. hispanica) and one Lamprothamnium species (L. papulosum). The latter, which indicates the period when water salinity was high in the lagoon, was found in the deepest sediment layers. An increase in the oospore abundance and diversity was observed in line with sediment depth. This indicates, on the one hand, that the lagoon went through different ecological stages (with important changes in salinity, mainly) and, on the other hand, the eutrophication process that the lagoon has been undergoing for at least the last 45 years, has progressively affected the abundance and diversity of the charophyte community.Las oósporas de carófitos y sus características (tamaño, forma, color, ornamentación de la pared, etc.) pueden persistir en los bancos de semillas del sedimento de ecosistemas acuáticos, y pueden ser utilizadas para identificar los diferentes táxones y obtener de este modo una aproximación a la composición florística de las comunidades de carófitos que colonizaron ambientes acuáticos en los que actualmente no existe vegetación acuática o se encuentra muy alterada. La Albufera de Valencia perdió hace muchos años las praderas de carófitos que cubrían sus fondos sin tener un estudio detallado de las mismas. Se han extraído diversos testigos de sedimento en tres puntos de esta laguna, se han caracterizado las oósporas y girogonitos encontrados y se ha estimado la densidad de oósporas-girogonitos en diferentes profundidades del sedimento. En total se han identificado 10 táxones, que corresponden: 6 al género Chara [Ch. vulgaris, Ch. hispida var. major, Ch. fragilis (Ch. globularis), Ch. hispida var. baltica, Ch. aspera y Ch. tomentosa]; una especie de Nitella (N. hyalina); 2 de Tolypella (T. glomerata y T. hispanica), y una de Lamprothamnium (L. papulosum). Esta última, indicadora de la época en la que la laguna poseía una mayor salinidad, se encontró en las capas más profundas del sedimento. Se ha observado un aumento del número y de la diversidad de oósporas en capas más profundas del sedimento, lo que indica, por un lado, que la laguna atravesó distintas fases ecológicas (con importantes cambios de salinidad principalmente) y, por otro, que el proceso de eutrofización que padece la laguna durante al menos los últimos 45 años afectó progresivamente a la abundancia y diversidad de carófitos

Influence of grazing on structure, composition and dynamics of vegetation in Mediterranean temporary pools (northern Tunisia)

Three temporary pools of Sejenane region (northern Tunisia) have been studied with the aims of characterizing their vegetation, and of specifying the impact of grazing on their structure, composition and dynamics. Permanent transects of quadrats have been surveyed in spring and summer during two (not-grazed pool) to three years (grazed pools). The vegetation of the three pools is organized in three concentric belts related to the topographic gradient. The between-years dynamics is strongly characterized by the alternation of distinct spring and summer vegetations. Grazing appears as the main control of the composition and structure of hydrophytic plant communities. It prevents the colonization by competitive, perturbation-sensitive species, and favours the persistence of annual, light-demanding dwarf plants. In order to protect the biodiversity of these rare habitats in Tunisia, it is necessary to maintain, through an adapted management of grazing, a landscape mosaic of grazed and not-grazed zonesTrois mares temporaires de la région de Sejenane (Tunisie septentrionale) ont été étudiées afin de caractériser leur végétation et de préciser l’influence du pâturage sur sa structure, sa composition et sa dynamique intra- et interannuelle. Des transects de quadrats permanents ont été suivis au printemps et en été durant deux (mare non pâturée) à trois ans (mares pâturées). Le cortège floristique des mares étudiées est organisé en trois ceintures concentriques liées au gradient topographique. La dynamique intra-annuelle de la végétation est nettement marquée par l’alternance de cortèges printaniers et estivaux distincts. Le pâturage apparaît comme le principal facteur contrôlant la composition et la structure des communautés végétales hydrophytiques. Il limite le développement des espèces compétitives sensibles aux perturbations et favorise le maintien d’une flore de petite taille, thérophytique et héliophile. Afin de préserver la biodiversité de ces habitats rares en Tunisie, il apparaît nécessaire de maintenir, par une gestion adaptée du pâturage, une mosaïque paysagère de zones non pâturées et pâturée

New finds of Chara oedophylla Feldmann in Tunisia: significance of sejoined gametangia

International audienceChara oedophylla was established as a new species after examination of specimens collected by L. Gauthier in Tunisia in 1926, which were kept at the herbarium of Paris. Subsequently, several scientists considered it to be a variety of Chara vulgaris. During fieldwork in northern Tunisia, we found the species close to its type locality (Mogods region). Detailed examination of abundant populations of these plants revealed their particular, specific morphology. Chara oedophylla is characterised by a sejoined arrangement of the gametangia (on different nodes), whereas they are conjoined in C. vulgaris. The antheridia are very large, as is usually the case in dioecious species. In contrast to C. vulgaris, where geminate oogonia are side by side, they are vertically geminated in C. oedophylla. The female nodes bear numerous swollen bract cells, hence the etymology of the species name. Here we provide an emended diagnosis that highlights the differences compared to C. vulgaris in order to maintain C. oedophylla as a valid species. The significance of sejoined gametangia with respect to speciation is discussed

New finds of Chara oedophylla Feldmann in Tunisia: significance of sejoined gametangia

Chara oedophylla was established as a new species after examination of specimens collected by L. Gauthier in Tunisia in 1926, which were kept at the herbarium of Paris. Subsequently, several scientists considered it to be a variety of Chara vulgaris. During fieldwork in northern Tunisia, we found the species close to its type locality (Mogods region). Detailed examination of abundant populations of these plants revealed their particular, specific morphology. Chara oedophylla is characterised by a sejoined arrangement of the gametangia (on different nodes), whereas they are conjoined in C. vulgaris. The antheridia are very large, as is usually the case in dioecious species. In contrast to C. vulgaris, where geminate oogonia are side by side, they are vertically geminated in C. oedophylla. The female nodes bear numerous swollen bract cells, hence the etymology of the species name. Here we provide an emended diagnosis that highlights the differences compared to C. vulgaris in order to maintain C. oedophylla as a valid species. The significance of sejoined gametangia with respect to speciation is discussed

Evidence of Chara fibrosa Agardh ex Bruzelius, an alien species in South France

The paper describes the discovery of a species of genus Chara, hitherto unknown in France. The morphological features of the plants and oospores are shown and identify the plant as Chara fibrosa ssp. benthamii, a tropical taxon, non-native to the European Charophyte flora. The ecological conditions of this particular find correspond to an artificial temporary pond located in the Crau plain, north of the Camargue. In contrast to the normal hydrological cycle ruled by local precipitation during winter, the studied pond is flooded from irrigation water in late spring and during summer. This context allowed C. fibrosa to out-compete the indigenous Chara species, Chara vulgaris and Chara globularis. The accidental introduction of C. fibrosa is attributed to original contamination from rice seed material imported to the nearby Camargue, rather than to dispersal by migratory water birds. Although the species has formed a very large population in that pond within a few years, it might not be classified as “invasive” because this occurrence is linked to a particular man-made habitat. However, spread of the species in the future, as a function of global warming related to climate change, cannot be excluded