Rivers
Résumé
Quaternary insect subfossils preserved in river deposits allow for the reconstruction of past environmental and climate changes. During the last glacial period, warm climate periods such as Dansgaard/Oeschger events or the Late-Glacial Interstadial have been recorded by the reappearance of temperate faunas, typical of very shallow lakes or low-energy anastomosing rivers. Inference models indicate temperatures reaching values similar to those of the present day. During cold periods such as the Younger Dryas, insect faunas were characterized by the presence of numerous cold-adapted species. Summer air temperatures ranged between 9 and 11°C. Winter temperatures were close to −11 to −12°C. During the early Holocene, temperatures rapidly increased to reach a thermal optimum (about 18-20°C) at around 8,000 year 14C bp. From the Middle Holocene, climate reconstructions are biased by increasing local impact of human activities on river water bodies. In France, cultivation and pastoralism led to the clearance of alluvial forest around 5,000-4,000 bp. This induced the disappearance of riffle beetles due to the rise in load in fines in the stream resulting from soil erosion. The fossil fauna from 2,000 bp to the present is mainly made of ruderal grassland associated taxa, dung-beetles and synanthropic taxa associated with food stored products. Keywords (separated by '-') Chironomids-Coleoptera-River-Climate change-Flood impact-Human impact Footnote Information The potential of biological remains in palaeoecological investigations of alluvial sedimentary deposits: with special emphasis to Insect data from France.