Identifying recent sources and fate of sedimentary nitrogen in the Baltic Sea based on organic matter elemental composition and nitrogen and carbon stable isotopes ratios
2020
Winogradow, Aleksandra | Pempkowiak, Janusz
Sedimentary nitrogen (SN) provenience and fate in surface and subsurface sediments collected from the Baltic Sea were assessed. SN and sedimentary organic carbon (SOC) concentrations, stable isotopic signatures (δ¹⁵NSN and δ¹³CSOC) and SOC/SN molar ratios, were determined in subsequent layers of twenty-four sediment cores dated with ²¹⁰Pb/¹³⁷Cs and fifty-seven surface sediments. Sedimentation rates in the range 66–736 g/m²yr⁻¹ (0.05–0.34 cm/year) were measured. Prolonged incubation of sediments in the laboratory led to a 17–37% decrease of SN in surface sediments, and no SN loss in sediments deposited before 1940. Decrease of δ¹⁵NSN on incubation (1‰ on average), and gradients of δ¹⁵NSN, between recent - surface (3.5‰) vs. 100 years old - subsurface (2.1‰) sediments were attributed to varying contributions of labile nitrogen to the SN pool. Annual deposition of SN to sediment surface and burial in subsurface sediments amounted, respectively, to 5 ± 2 g/m² and 3.5 ± 1 g/m².
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