High <i>δ</i> ¹⁵ N and <i>δ</i> ¹³ C Values in Aurochs, Cattle and Sheep Bones from Salt Marshes in the North of The Netherlands

185 pairs of δ¹³C and δ¹⁵N values for aurochs, cattle and sheep bones from the northern Netherlands were studied to establish the influence of salt marsh grazing on bone δ¹³C and δ¹⁵N values. The observed values proved significantly increased compared to livestock that grazed inland. The δ¹³C and δ¹⁵N values of animals grazing former salt marshes were significantly less increased than those grazing the unembanked salt marsh. Absent regular salt marsh flooding may explain the reduced δ¹³C increase in bones of animals grazing there. The δ¹⁵N values of ruminants grazing the embanked salt marshes continued to be increased, presumably due to persisting saline water at shallow depths. The δ¹³C values of the salt marsh grazing ruminants correspond with a δ¹³C increase of 5‰ compared to eleven modern salt marsh plants from Schiermonnikoog studied in this paper. The δ¹⁵N values of the eleven Schiermonnikoog salt marsh plants proved variable, on average too low to explain the observed 3.5‰ increase in δ¹⁵N values. This suggests that vegetation δ¹⁵N values cannot be the only cause of the high δ¹⁵N values observed in salt marsh ruminants. Other processes may be responsible for the high δ¹⁵N values of salt marsh grazing ruminants as well.