Spatial distribution, chemical speciation and source apportionment of carbon, nitrogen and phosphorus in surface sediments of northern Beibu Gulf, South China

This study presents the spatial distribution and chemical speciation of carbon (C), nitrogen (N) and phosphorus (P) in sediments, and traces the origins of sedimentary organic matter (SOM) with C-N isotopes composition and elemental ratios in the northern Beibu Gulf. The spatial distribution of biogenic elements was significantly related to the grain size composition and terrestrial inputs. The liable nitrogen (LN) accounted for 20.74 f 14.84 % of total nitrogen (TN), and organic matter-sulfide form-N (OSF-N) was the dominant part among four LN forms. The bio-available P (BAP) accounted for 76.49 f 5.92 % of total phosphorus (TP), and the average proportions of P fractions followed the order of organic P (OP) > Fe-bound P (Fe-P) > authigenic P (Ca-P) > detrital P (De-P) > exchangeable P (Ex-P). The SOM was mainly derived from terrestrial sources in Lianzhou Bay and Maowei Sea, whereas marine phytoplankton primarily contributed to the SOM in other coastal bays.