Deposition, return flux, and burial rates of nitrogen and phosphorus in the sediments of two high-Arctic fjords

Abstract

Summary: The aim of this study was to determine the burial rates of nitrogen (N) and phosphorus (P) in the sediments of two high-latitude fjords: Hornsund and Kongsfjorden (Spitsbergen). Both deposition to sediments and the return flux from sediments to the water column of the various species of these elements were, therefore, quantified. The burial rate was then calculated as the difference between deposition and return flux. The required concentrations of N and P species were measured in surface sediments, in pore water extracted from the sediments, and in the above-bottom water at sampling stations situated along the axes of the fjords.Annual deposition to sediments ranged between 2.3–8.3 g m−2 for N and 0.9–2.8 g m−2 for P. The nitrogen return fluxes ranged from 0.12 to 1.46 g m−2 y−1. At most stations, the N flux was predominantly of dissolved organic (about 60–70%) rather than inorganic N. The P return flux varied between 0.01 and 0.11 g m−2 y−1, with organic species constituting 60–97%. The N and P burial rates differed between fjords: 2.3–7.9 g N m−2 y−1 and 0.9–2.8 g P m−2 y−1 in Hornsund vs. 0.9–1.3 N g m−2 y−1 and 1.0–1.2 g P m−2 y−1 in Kongsfjorden. This was accompanied by a different efficiency of N and P burial – higher in Hornsund than in Kongsfjorden, in both cases. This suggests differences in the quality and quantity of N and P organic species deposited to sediments and therefore differences in the intensity of their mineralization and/or decomposition. Keywords: Hornsund, Kongsfjorden, Sedimentary nitrogen and phosphorus, Pore water, Concentrations, Nutrients