Natural variations in ¹⁵N content of riverine and estuarine sediments

A study of the natural variations of ¹⁵N in the sediments of the river Tamar estuary and its catchment, south-west England, is described. The mean δ¹⁵N for freshwater sediments was +2·3‰ (SD ± 0·9) and distinct from the majority of estuarine sediments. Three catchment areas that together comprise the riverine system could be distinguished by a combination of the δ¹⁵N of the sediments and the riverine NO₃^- concentrations. Estuarine surface sediments fell into three groups: upper-estuary (mean δ¹⁵N = 5·6‰); mid-estuary (mean δ¹⁵N = 2·7‰) and lower-estuary (mean δ¹⁵N = 5·3‰). These distributions confirm earlier, non-isotopic, observations of the complex patterns of transportation of surface sediments in this estuary.