Simulated Study Of Effects Of Benthic Animals On Degradation Of Algal Lipids In Seasonal Hypoxia Environment

In this study, Skeletonema costatum was applied as research object to investigateeffect of benthic animals on degradation of organic matter in sediment in seasonalhypoxia environment. The degradation processes of S.costatum in simulatedincubation microcosm with and without the existence of Metapenaeus ensis undervarious oxygen saturations were compared. The degradations of four typical fattyacids and neutral lipids in the incubation systems with100%,50%,25%and0%oxygen saturations were tracked. The results showed that:(1) Bioturbation of benthic animals promoted transfer of lipids from surfacesediments to subsurface sediments and suspend particles, and then changed thedistributions of lipids. The activities of M. ensis weakened and much less lipids weretransferred into subsurface sediment with decrease of oxygen saturations. In detail,under100%oxygen saturation, the concentrations of fatty acids and neutral lipids inthe surface sediments declined rapidly, and a large amount of fatty acids and neutrallipids were transferred into subsurface sediments and suspend particles. Under50%oxygen saturation, much less amount of lipids was transferred by benthic animals.Suspended particles were only produced at early incubation and algal lipids weredetected in them. Although less amount of algal lipids was transferred into subsurfacesediment under50%oxygen saturation, the difference of the concentrations of algallipids in subsurface sediment under100%and50%oxygen saturations wasinsignificant, indicating slow degradation of lipids in subsurface sediment under50%oxygen saturation. Under25%and0%oxygen saturations, no suspend particles wereproduced and no algal lipids were detected in subsurface sediments.(2) Activities of benthic animals promoted degradation of biomarkers under100%oxygen saturation. The degradation rate constants kavs of fatty acids in experimental cores were1.2-1.7times than those in control cores, especially for14:0and16:0. The degradation rate constants kavs of neutral lipids in experimental coreswere2.2-2.8times than those in control cores. However, in hypoxia incubationsystem with50%oxygen saturation, the activities of M. ensis weakened eventuallyuntil their death in the initial incubation. Before the death of M.eniss, theirbioturbation buried more organic matter in the subsurface sediment and thendecreased degradation rate. The kavof fatty acids and neutral lipids in cores were lessthan or to control under25%and0%oxygen saturation environment, M. ensis diedsoon and had little effect on organic matter degradation, the degradation of fatty acidsand neutral lipids were mainly controlled by microorganism.(3) Besides bioturbation, redox regime and structure of lipids had importanteffect on degradation. In different environment, lower degradation rate constants offatty acids and neutral lipids were found in lower oxygen saturation systems,especially for neutral lipids. The kavs of fatty acids with different structure varieddramatically in the same system. The kavs of unsaturated fatty acids20:5and16:1(7)were higher than those of saturated fatty acids. Because of more double bonds in20:5, its degradation rate constant was also higher. The existence of benthic animalsdid not change the difference caused by the compound structure. Degradation rateconstants ranged from0.25to0.52for polyunsaturated fatty acids and from0.11to0.34for saturated fatty acids,kavrange, indicating significant effect of double bondson the degradation of fatty acids. Degradation rate constants of neutral lipids withdifferent structure varied insignificantly in the same experimental or control coresunder the same oxygen saturation, indicating little effect of molecule structure ofneutral lipids on their degradation.