The palaeoenvironments of coastal lagoons in the southern Baltic Sea,I. The application of sedimentary Corg/N ratios as source indicators of organic matter

C/N ratios of organic matter sources in coastal lagoons and their drainage areas in the southern Baltic Sea region are investigated to determine the origin of organic matter (i.e. terrigenous or marine) in the sediments of the lagoons. These ratios are compared with δ¹³C values in the area. Terrestrial plants in the study area show C/N ratios between 10 and 85, whereas aquatic macrophytes have values in the range of 6 to 44. Peat and shore vegetation have C/N ratios between 15 and 16, and plankton shows values close to 6. In conjunction with δ¹³C values, the C/N ratios in the sediments allow the reconstruction of the Holocene palaeoenvironments and palaeoecology in the lagoons (Oder Estuary and Greifswalder Bodden). Distinct stages in the development of the water bodies, resulting from sea level changes in the region, can be derived: post-glacial lake stages with sandy sedimentation, lacustrine phases with high autochthonous productivity, terrestrial stages with peat formation, sedimentation as a result of marine transgression, and brackish sedimentation after the formation of sand spits and barrier islands. The application of C_org/N_tot ratios instead of C_org/N_org does not have any significant influence on the interpretation of the data and may thus be used in the coastal sediments of the southern Baltic Sea after having applied the test procedures presented in this study.