The Study On The Spatial And Temporal Distributions Of Anammox In The East China Sea By Ladderane Lipids

Anaerobic ammonium oxidation （anammox） is an oxidation process ofammonium under anoxic conditions with nitrite as the electron acceptor and releasingof N2. It occurs in the anammoxosome of the anammox bacteria and plays animportant role on the marine nitrogen cycle. Ladderane lipids, the specific membranelipids unique to anammox bacteria, have been successfully used as biomarkers foranammox process in marine environments. However, little is known on theimportance of anammox in the present and past marine nitrogen cycles in the EastChina Sea （ECS）. In this study, ladderane core lipids in the surface sediments,suspended particles and one sediment core （T06,122°40.248ˊE,29°29.975ˊN,water depth48.8m） have been measured and compared with some indicators oforganic matter and dissolved oxygen for studying the temporal and spatialdistributions of anammox and its influencing factors.The detection of ladderane lipids in all the surface samples suggested thewidespread occurrence of the anammox in the ECS. The spatial distribution of theladderane lipids was similar to that of TOC（Total Organic Carbon）, marinebiomarkers （A+B+D （alkenones+brassicasterol+dinosterol）, GDGTs, crenarchaeol）and terrestrial biomarker (C₂₇+C₂₉+C₃₁n-alkane), with high values locating in theYangtze River Delta southern mud area, the Zhejiang-Fujian mud area and the mudArea Southwest off Cheju Island. The results suggested that the anammox may beattributed to the inputs of nutrients via Changjiang river, costal upwelling offZhejiang-Fujian and Cheju Island and the decomposition of organic matter, and thenthe enhanced marine productivity and lower dissolved oxygen. The estimatedsynthesis temperature of ladderane lipids based on NL5index （the iNdex of Ladderanelipids with5cyclobutane rings, the ratio of the related ladderane lipids with different chain length） indicated that anammox most likely occurs in the water column, butlower levels of anammox bacteria live in the sediments. In addition, the frequentdetection of ladderane lipids in the suspended particles also suggested the occurrenceof stronger anammox in the water column. For lack of the sites of the suspendedparticles, it is still difficult to describe the distribution of anammox in the watercolumn.The ladderane records in T06revealed the occurrence of anammox in the last100years, with an increasing trend in recent years. In1898-1960, anammox basicallyremained stable and then began to increase since1960, especially from1980, Thetemporal trends are similar to all the selected marine biomarkers （A+B+D, GDGTsand crenarchaeol）. The coincidence on the temporal patterns of anammox and marineproductivity suggested the occurrence of their relationship. That is, the increasedhuman activities which bring more and more nutrients influx to the ECS and then leadto the enhanced marine productivity should be involved for the enhanced anammox.Meanwhile, the respiration of the enormous plankton and decomposition of theorganic matter often lead to severe oxygen depletion and then are favorable foranammox. For TOC and terrestrial biomarker of C₂₇+C₂₉+C₃₁n-alkane, no significantrelationship between them and ladderane lipids has been observed. In all, the resultsin the present study indicated that anammox is closely related to the marineproductivity, and the dissolved oxygen and the nutrients （i.e. NH₄⁺and NO₂^-） may bethe controlling factors on anammox, but further research is needed. Anammox, inaddition to denitrification, seems to play an important role on the significant loss ofnutrient nitrogen in the East China Sea in present and past.