Analysis of coleopterans from Late Holocene natural spring deposits in south-central Sweden

The usage history of a natural spring deposit in associated glacial till was investigated via analysis of coleopteran remains found in peat. This material was recovered during archaeological excavations in a spring outflow in south central Sweden. The geographical region of southern Sweden has been heavily affected by uplift following the terminal glaciation (Weichselian) in Scandinavia, with the study area for this project having risen above sea level about 1200 BC. The spring was found in connection to the northern part of a large settlement and religious area, dating from the Younger Bronze Age and Pre Roman Iron Age (1100–300 BC). However, the area has been used for agricultural land up until the present day. Sampling was conducted for interpretation of the usage history of the site, with the insect fragments showing exceptional preservation as a result of unusual conditions in the sediments. ¹⁴C-dating from the lower to upper part of the spring yielded a stratigraphic range of 670–870 to 660–810 AD respectively. A half-circle boulder construction provides clear evidence that the spring was used early in prehistory, probably during the Bronze Age, and potentially excavated at irregular periods. The coleopteran assemblage was dominated by beetles indicative of open landscapes, grazing land, and forested environments. This closely resembles the vegetation setting of today, in which the spring is situated on the border between arable land and mixed deciduous and coniferous forest. A high frequency of carabid beetles suggests that the spring may have functioned as a pitfall trap, and correlated well with the relative inorganic to organic compound composition of the ground conditions. The spring was probably abandoned in the late Iron Age (600–800 AD). Identification of two red-listed threatened species that are not present in the current fauna implies that radical change in the agricultural landscape over the last 1200 years could be negatively affecting diversity dynamics within the local fauna.