Intraregional variability in chironomid-inferred temperature estimates and the influence of river inundations on lacustrine chironomid assemblages.

Floodplain lakes are rarely analysed for fossil chironomids and usually not incorporated in modern chironomid-climate calibration datasets because of the potential complex hydrological processes that could result from flooding of the lakes. In order to investigate this potential influence of river inundations on fossil chironomid assemblages, 13 regularly inundated lakes and 20 lakes isolated from riverine influence were sampled and their surface sediments analysed for subfossil chironomid assemblages. The physical and chemical settings of all lakes were similar, although the variation in the environmental variables was higher in the lakes isolated from riverine influence. Chironomid concentration and taxon richness show significant differences between the two classes of lakes, and the variation in these variables is best explained by loss-on-ignition of the sediments (LOI). Relative chironomid abundances show some differences between the two groups of lakes, with several chironomid taxa occurring preferentially in one of the two lake-types. The variability in chironomid assemblages is also best explained by LOI. Application of a chironomid-temperature inference model shows that both types of lakes reconstruct July air temperatures that are equal to, or slightly underestimating, the measured temperature of the region. We conclude that, although there are some differences between the chironomid assemblages of floodplain lakes and of isolated lakes, these differences do not have a major effect on chironomid-based temperature reconstruction. © 2007 Springer Science+Business Media B.V

Response of littoral chironomid community and organic matter to late glacial lake level and environmental changes at Lago dell'Accesa (Tuscany, Italy).

International audienceThis study focuses on the response of lacustrine littoral chironomid communities to late glacial changes in limnological, environmental and climate conditions in the Mediterranean context. Late glacial chironomid (Diptera: Chironomidae) assemblages, organic petrography and geochemistry were analysed in a sediment core from the littoral zone of Lago dell'Accesa (Tuscany, Italy), where the lake-level fluctuations and the vegetation history have been previously reconstructed. Comparison of the chironomid stratigraphy to other proxies (pollen assemblages, organic petrography and geochemistry, lake-level) and regional climate reconstruction suggested the predominant influence of lake-level changes on the littoral chironomid fauna. The main lowering events that occurred during the Oldest and the Younger Dryas were followed by higher proportions of taxa typical of littoral habitats. A complementary study of organic matter suggested the indirect impact of lake-level on the chironomids through changes in humic status and habitat characteristics, such as the type of substrate and aquatic macrophyte development. Several chironomid taxa, such as Glyptotendipes, Microtendipes and Cricotopus type patens, were identified as possible indicators of low lake-level in the late glacial records. Nevertheless, this study suggested that parallel analyses of organic matter and chironomid assemblages may be needed to circumvent misinterpretation of littoral chironomid assemblage stratigraphy. There was a weak response of the chironomid assemblages to small lake-level lowerings that corresponded to the Older Dryas and Preboreal oscillations. A higher level of determination, e.g. to the species group level, may be necessary to increase the sensibility of the indicators to lake-level changes

Les affluents des cours d'eau méditerranéens: rôle dans le maintien de la diversité du macrobenthos

International audienceThe taxonomic richness erosion and the role of tributaries in the maintenance of the taxonomic richness were considered in a Mediterranean catchment in southeastern France. Nine stations were chosen along the Arc stream (three stations downstream from an organic effluent and one station upstream from the pollution source) and on two groups of tributaries (three intermittent and two perennial). High biodiversity erosion was noticed in the main stem, revealing diffuse sources of pollution added to the expected effect of the localized organic pollution. Jackknife richness estimator and beta diversity indicated that the intermittent tributaries had the highest richness values and harboured 70% of the taxa recorded at the catchment scale. The intermittent flow tributaries seem to play a major role in maintaining the taxonomic richness in such catchments, highly impacted by anthropogenic activities. The detailed examination and the preservation of these ecosystems should be an important step in catchment management, and support the need for catchment-scale conservation of freshwater invertebrates.L'érosion de la richesse taxinomique ainsi que le rôle des affluents temporaires dans le maintien de cette richesse taxinomique on été étudiés dans un petit bassin versant méditerranéen du Sud-Est de la France. Neuf stations d'études on été choisies le long de la rivière Arc (une station en amont de la station d'épuration de Trets et trois en aval), ainsi que sur deux types d'affluents (trois affluents temporaires et deux permanents). Une importante érosion de la richesse taxinomique a été observée le long de la rivière Arc, même dans la station située en amont de la source de pollution organique localisée ; ceci suggère l'existence de pollutions diffuses dans le bassin versant. L'estimation de la richesse par la méthode Jackknife ainsi que la diversité bêta montrent que les affluents temporaires abritent 70% des macroinvertébrés benthiques recensés dans cette partie du bassin versant. Ces affluents semblent jouer un rôle important dans le maintien de la richesse taxinomique dans ce type de bassin et plaide pour la conservation de la faune benthique d'invertébrés à l'échelle du bassin versan

Hydroclimatic changes in Iran, during the Lateglacial/Holocene transition, based on chironomid analysis: Comparison of records from Lake Neor (NW Iran) and Lake Arjan (SW Iran)

International audienc

Halmyris: Geoarchaeology of a fluvial harbour on the Danube Delta (Dobrogea, Romania)

In Northern Dobrogea, north of the Dunavăţ promontory, the Roman fortress of Halmyris was founded in the late 1st century AD on a Getic settlement dating to the middle of the 1st millennium BC, probably associated with a Greek emporium of the Classical and Hellenistic periods. At the time of the foundation of Halmyris, the Danube delta had already prograded several kilometres to the east leading to the progressive retreat of the sea and the formation of a deltaic plain characterised by numerous lakes and river channels. Here, we present the results of a multiproxy study combining sedimentology and palaeoecology to (1) understand the evolution of fluvial landscapes around Halmyris since ca. 8000 years BP and (2) identify the fluvial palaeoenvironments close to the city in Getic/Greek and Roman times, in order to locate and characterise the waterfront and the harbour. Our overriding objective was to improve understanding of human–environment relations in river delta settings. We demonstrate that Halmyris, protected by the Danubian floods due to its location on a palaeo-cliff top, had direct access to the river. A secondary channel of the Saint George, flowing north of the site, has been elucidated between the 7th century BC and the 7th century AD and could have been used as a natural harbour