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International audience; Palaeoecology is increasingly contributing to conservation biology and restoration ecology by extending the recent annual to decennial records of ecological observations to centennial and millennial time scales. One of the almost neglected potential applications of palaeoecological investigations in conservation biology is the discovering of hidden species in subrecent fossil records. Such discoveries can be common in biodiversity hotspots in which the fauna and flora are not still fully known. In this study, we present the case of the liverwort Riella in continental southwest Asia (Iranian plateau), a very vulnerable taxon growing and reproducing under very special ecological circumstances. Our study adds two new species of Riella (R. echinata and R. helicophylla) in addition to the formerly reported R. cossoniana, to the subfossil bryophyte flora of Iran. We demonstrate the important contribution that the genus has played in the history of wetland flora of the semi-arid to arid areas of Iran during the late Quaternary. We further demonstrate the possibility that it is still thriving in many wetland systems and may need to be discovered and then protected in its potential habitats. We suggest that in the biodiversity hotspots of lower latitudes, more attention has to be paid to taxonomic identification of species to reveal the hidden part of the biodiversity for defining better conservation strategies for vulnerable aquatic ecosystems such as the seasonal wetland systems.

International audience; The late glacial-early Holocene transition is a key period in the earth's history. However, although this transition is well studied in Europe, it is not well constrained in the Middle East and palaeohydrological records with robust chronologies remain scarce from this region. Here we present an interesting hydrobiological record showing a major environmental change occurring in the Dasht-e Arjan Wetland (southwestern Iran, near to Persepolis) during the late glacial-early Holocene transition (ca. 11 650 years cal BP). We use subfossil chironomids (Insecta: Diptera) as a proxy for hydrological changes and to reconstruct lake-level fluctuations. The Arjan wetland was a deep lake during the Younger Dryas marked by a dominance of Chironomus plumosus/anthracinus-type, taxa adapted to anoxic conditions of deep waters. At the beginning of the Holocene, a drastic decrease (more than 80% to less than 10%) of Chironomus plumosus/anthracinus-type, combined with diversification of littoral taxa such as Polypedilum nubeculosum-type, Dicrotendipes nervosus-type, and Glyptotendipes pallens-type, suggests a lake-level decrease and a more vegetalized aquatic environment. We compare and contrast the chironomid record of Arjan with a similar record from northwestern Iran. The palaeoclimatic significance of the record, at a local and regional scale, is subsequently discussed. The increase in Northern Hemisphere temperatures, inferred by geochemical data from NGRIP, at the beginning of the Holocene best explains the change from the Younger Dryas highstand to early Holocene lowstand conditions in the Dasht-e Arjan wetland. However, a contribution of the meltwater inflow from small local glaciers in the catchment basin is not excluded.; La transition tardiglaciaire-Holocène précoce représente une période clé de l'histoire de la terre. Si cette transition est bien étudiée en Europe, ce n'est toutefois pas le cas au Moyen-Orient, et les profils paléohydrologiques associés à des chronologies robustes demeurent rares pour cette région. Nous présentons un profil hydrobiologique intéressant qui montre un important changement environnemental s'étant produit dans la zone humide de Dasht-e Arjan (sud-ouest de l'Iran, près de Persépolis) durant la transition tardiglaciaire-Holocène précoce (vers 11 650 ans cal BP). Nous utilisons des subfossiles de chi-ronomidés (insectes : diptères) comme indicateurs de changements hydrologiques et pour reconstituer les fluctuations du niveau de lacs. Le milieu humide d'Arjan était un lac profond durant le Dryas récent, caractérisé par une prépondérance de taxons de type Chironomus plumosus/anthracinus adaptés aux conditions anoxiques des eaux profondes. Une baisse drastique (de plus de 80 % à moins de 10 %) de ces taxons au début de l'Holocène, combinée à la diversification de taxons littoraux de types Polypedilum nubeculosum, Dicrotendipes nervosus et Glyptotendipes pallens, indiquerait une baisse du niveau du lac et un milieu aquatique plus végétalisé. Nous comparons le profil des chironomidés d'Arjan à un profil semblable du nord-ouest de l'Iran. La signification paléoclimatique du profil, aux échelles locales et régionales, est ensuite abordée. L'augmentation des températures dans l'hémisphère nord au début de l'Holocène, inférée à partir de données géochimiques du NGRIP, est ce qui explique le mieux le passage de conditions de haut niveau du Dryas récent aux conditions de bas niveau de l'Holocène précoce dans la zone humide de Dasht-e Arjan. Un effet de l'apport d'eau de fonte de petits glaciers locaux dans le bassin versant n'est toutefois pas exclu. [Traduit par la Rédaction] Mots-clés : Dryas récent, changement climatique, karst, changement du niveau des lacs, Zagros.

International audience; Palynological and geochemical analyses provide valuable information about modern and past climatic regimes and vegetation. The impact of climate and humans on past vegetation in the semi-arid areas of northwestern Iran has received increased interest in the wake of warming temperatures in the Middle East. Palynological and down-core XRF elemental abundances from a peat core from Lake Neor enabled a reconstruction of vegetational changes of the past 7000 years over the highlands of northwestern Iran. Periods of increased arboreal pollen (AP) types and high (Artemisia + Poaceae)/Chenopodiaceae ratios along with low titanium abundances, high percentages of total organic carbon, more negative δD values, and higher carbon accumulation rates suggest a relatively wet climate. These conditions have persisted during the periods 6700-6200, 5200-4450 and 3200-2200 cal a BP. The overall low AP values, substantial rise of Chenopodiaceae, high Ti abundances and low values of palaeo-redox proxies, are all evidences of a drier climate, as has been reconstructed for the periods 6200-5200 and 4030-3150 cal a BP and the last 2200 years. An important feature of the last centuries is the increase of anthropogenic and pastoral indicator pollen types. Our results may provide basic data to predict future trends in vegetation dynamics under future climate change in western Asia.

International audience; Sedimentological (dry density, micro-fa-cies analysis on thin-slides, X-ray diffraction, layer counting) and elemental analyses (X-ray fluorescence) of a 3.5-m-long sediment core (MAH-B) from saline Lake Maharlou (SW Iran) were used to infer hydrological changes over the last * 3800 years. The sediment consists of thin, alternating beds of evapor-ites (halite, gypsum), carbonates (calcite, aragonite) and detrital minerals (quartz, muscovite, chlorite). We interpret the data with respect to three main hydrologic conditions: (1) nearly complete desiccation of the lake, marked by frequent halite layers, (2) hypersaline conditions marked by gypsum abundance, (3) wet conditions, characterized by high river-borne terrige-nous sediment input with high potassium content. Distinct flood layers indicate fluvial activity. From about 3800-2000 cal year BP, terrigenous sediment supply was high, with peaks at 3700-3650, 3500-3450, and 3400-3250 cal year BP. Evaporative conditions were not common. From ca. 2000 cal year BP to present, detrital minerals are less abundant, and the increase in gypsum abundance suggests drier climate with enhanced evaporation. Frequent desiccation events occurred from 1100 to 700 cal year BP. The late Holocene hydrology of Lake Maharlou corresponds well with records of dune formation and phases of river alluviation in Iran and the Arabian Peninsula, and with regional speleothem records. In addition to the influence of climate change on the lake hydrology, ancient humans modified water drainage in the catchment. Periods of subterranean tunnel (qanats) use correspond to dramatic shrinkage of the water body. We propose that climate changes drove long-term water shortages that were enhanced by anthro-pogenic activities, leading to more frequent desiccation of the lake during the last millennium.

International audience; Palustrine carbonates are frequently found with active and dried karstic springs in the foothills of the mountains bordering the Persepolis Basin, southwest Iran. A combination of geological conditions favours their formation, including (i) the presence of karstic limestone aquifers in the limbs of anticlines cut through by fault systems; (ii) very gentle slopes from the spring resurgence point towards the centre of the alluvial plain, creating a flat waterlogged area; and (iii) a semiarid climate with marked precipitation seasonality or significant fluctuations in water discharge and wetland water table. We suggest the term "anastomosing wetlands" or "anastomosing palustrine environments" to denote the studied karstic spring-fed carbonate wetlands, because of similarities with anastomosing river systems in aerial view. The common presence of extended anasto-mosing wetland carbonates in the Persepolis Basin and adjacent basins in the central and southern Zagros suggests that they can play an important role in the geological records of collision-related basin-and-range settings dominated by karstic limestones. Karstic spring wetlands are a main source of fresh water hosting a rich biodiversity, which attracts human communities, whose impact is visible in the archaeological material imbedded in the wetland stratigraphy. Fresh water availability, through these spring wetlands, partly explains why the semiarid Persepolis region was selected by successive civilizations, from Elamites to Persians until early Islamic entities, to establish regional centres throughout the period from the third millennium B.C. to the first millennium A.D. Only a few of these ecosystems have survived the intensive human activities of recent decades.; Des carbonates palustres sont fréquemment associés à des sources karstiques actives et asséchées dans le contrefort des montagnes bordant le bassin de Persépolis, dans le sud-ouest de l'Iran. Une combinaison de conditions géologiques favorise leur formation, à savoir : i) la présence d'aquifères de calcaires karstiques dans les flans d'anticlinaux découpés par des systèmes de failles, ii) les pentes très douces des points de résurgence de sources vers le centre de la plaine alluviale, créant une zone plane saturée et iii) un climat semi-aride caractérisé par une saisonnalité marquée des précipitations ou d'importantes fluctuations de l'écoulement de l'eau et de la nappe phréatique dans les zones humides. Nous proposons le terme « zones humides anastomosées » ou « milieux palustres anastomosés » pour désigner les zones humides à carbonates karstiques alimentées par des sources en raison de similitudes qu'elles présentent en vue aérienne avec des réseaux hydrographiques anastomosés. La présence répandue de carbonates dans les zones humides anastomosées du bassin de Persépolis et des bassins voisins des parties centrales et sud des monts Zagros indiquerait qu'ils peuvent jouer un rôle important dans les profils géologiques des milieux de bassins et montagnes. Ces milieux sont associés à des collisions tectoniques dans lesquels prédominent des calcaires karstiques. Les zones humides karstiques alimentées par des sources constituent une source d'eau douce majeure abritant une grande diversité). biologique qui attire les collectivités humaines, dont l'impact est visible dans le matériel archéologique présent dans la stratigraphie des zones humides. La disponibilité d'eau douce qu'offrent ces zones humides alimentées par des sources explique en partie pourquoi la région semi-aride de Persépolis a été retenue par des civilisations successives, des Élamites aux Perses jusqu'aux premières entités islamiques, pour y établir des centres régionaux durant toute la période allant du 3 e millénaire avant notre ère au 1er millénaire de notre ère. Seuls quelques-uns de ces écosystèmes ont survécu à l'intense activité humaine des récentes décennies.