Agricultural lime disturbs natural Sr isotope variations – Now what?

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The use of 87Sr/86Sr in prehistoric mobility studies requires accurate strontium (Sr) reference maps, which are often based on present-day surface waters. However, the use of modern agricultural lime in calcium-poor soils can substantially change the 87Sr/86Sr compositions of surface waters. Water unaffected by agriculture in western Denmark has an average 87Sr/86Sr ratio of 0.7124, whereas water from nearby farmland has an average of 0.7097. Moreover, a systematic investigation of a 1.5 km segment of a river originating in a forest—Karup Å shows that 87Sr/86Sr ratios decrease abruptly from 0.7131 to 0.7099 upon entering lime-treated farmland. Calculations based on these data indicate that more than half of the Sr in the river’s catchment area comes from agricultural runoff.

Thus, Sr-based mobility and provenance studies in regions with calcium-poor soils should be reassessed; however, the data still hold valuable information. For example, reinterpreting the iconic Bronze Age women at Egtved and Skrydstrup using values unaffected by agricultural lime indicates that it is most plausible that these individuals originated close to their burial sites, and not far abroad as previously suggested. Yet the results are interesting, in particular, The Egtved Girl’s, which show that she may have lived part of the year in one area—likely the nearby river valley, and part of the year in another place—likely the local plateau, perhaps in the practice of transhumance farming. Hence, the knowledge that agricultural lime affects natural Sr variations does not change that Sr-based mobility and provenance studies are very much worth doing. However, future studies should take great care in sampling of waters, plants, soils, bones, etc. for Sr-reference maps in areas affected by modern-day agriculture.
Original languageEnglish
Publication year14 Jun 2019
Publication statusPublished - 14 Jun 2019
Event15th Nordic Bronze Age Symposium - LUX, Lund University, Lund, Sweden
Duration: 11 Jun 201915 Jun 2019
Conference number: 15
https://konferens.ht.lu.se/15th-nordic-bronze-age-symposium/

Conference

Conference15th Nordic Bronze Age Symposium
Number15
LocationLUX, Lund University
CountrySweden
CityLund
Period11/06/201915/06/2019
Internet address

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