High δ15N and δ13C 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 northernNetherlands 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 ofthe 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 lowto 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.