Contribution of vascular-plant carbon to surface sediments across the coastal margin of Cyprus (eastern Mediterranean)

Abstract

Elemental carbon and nitrogen and lignin-phenols were measured in sediments (whole and fractionated) collected from the coast of Cyprus (eastern Mediterranean) in 1997, to determine the sources, fate and distribution of vascular plant-derived organic matter in a system with virtually no river inputs. There was a significant increase in percent fines (<63 μm) in sediments with increasing distance offshore, reflecting the effects of hydrodynamic sorting processes. Although there were no significant differences between the mean total organic carbon (TOC) percentage of whole sediment (0.8±0.2%) and the <63 μm fraction (1.0±0.3%), mean lignin-phenol yields ( Λ) for whole sediments at all stations (0.11±0.07) were significantly higher than in the <63 μm fraction (0.02±0.01). The Λ values ranged from 0.09 to 0.72 and from 0.01 to 0.05 in whole sediment and the <63 μm fraction, respectively. Mean ratios of vanillic acid/vanillin (Ad/Al) v, indicative of the amount of oxidative degradation of the lignin component, were significantly higher in the <63 μm fraction (0.31±0.11) than whole sediment (0.23±0.10). The range of S/V (0.37–0.72) and C/V (0.02–0.06) ratios for both sediment types were within the range of ratios found in the tissues of the three dominant seagrasses ( Cymodocea nodosa, Halophila stipulaceae and Posidonia oceanica), S/V (0.42–1.85) and C/V (0.02–0.08). High syringyl/vanillyl (S/V) ratios (indicative of angiosperm tissues) were found in sediments across all stations along the transect, indicating that seagrass-derived lignin was transported to at least 6 km offshore. Higher (Ad/Al) v ratios in offshore fine particles compared to nearshore whole sediments suggested that there was subaqueous oxidative degradation of lignin which occurred during transport of fine particles across the Cyprus margin. Although biodegradation is likely to be an important mechanism for lignin decay, the high transparency of the ultraoligotrophic waters of Cyprus may have also allowed for photooxidation of lignin-phenols, a process less likely to occur in turbid coastal waters receiving high riverine inputs.