Palaeoenvironmental reconstruction from Eemian insect remains at Ejstrup, Denmark: Evidence for a riverine setting

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Abstract
The freshwater environments of the Eemian are well documented, although mostly focussed on lakes. Here, we present results from lake sediments of dark grey, laminated, organic‐rich medium sand, on top of very dark grey gyttja at the site of Ejstrup, west of Kolding, Denmark. Based on pollen counts, the sediments were biostratigraphically classified as mid‐Eemian. Despite the lake deposition, the assemblage of aquatic insect subfossils clearly indicates a river environment. The aquatic assemblage was rich, including five beetle taxa, 23 caddisfly taxa and 29 taxa of dipterans (non‐biting midges, blackflies and brine flies). Specifically, analyses of the species' habitat traits point to a 15–25 m wide river, likely a tributary to a lake. This lowland river was likely fast‐flowing, and meandering, with a sequence of riffle areas containing boulders, stones and gravel, separated by areas of sand, and bordered by silty/muddy areas along the banks. Furthermore, the riverbed may have contained a large amount of submerged dead wood but only sparse vegetation, due to an overall dense riparian canopy dominated by Carpinus betulus , Corylus avellana and Alnus sp. Based on the Trichoptera species, we reconstruct a mid‐Eemian July mean air temperature of 18.1°C, that is, 1.2°C higher than the 1991–2020 average. The Eemian river environment, assumed to be unaffected by human influence, may serve as a useful reference for the present‐day restoration of heavily anthropogenically impacted Danish and European rivers.

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