The Study On The Spatial And Temporal Distribution Of Anammox In The Pearl River Estuary By Ladderane Lipids

Anaerobic ammonium oxidation (anammox) is the anaerobic oxidation ofammonium by nitrite with dinitrogen gas as the end product, and it is an importantprocess of removing fixed nitrogen from the nature environment. Ladderane lipids,unique to anammox bacteria, consist of three or five linearly fused cyclobutane ringseither ester-or ether-linked to the glycerol backbone via an alkyl chain, and have beenwidely applied as biomarkers to indicate the anammox activity in differentenvironment. So far, ladderane lipids have been detected in the water column andsurface sediment of many seas, suggesting that it has an important indicatingsignificance for the nitrogen cycle and reconstruction of the anammox. However, littleis known on the important of anammox in the present and past nitrogen cycles in thePearl River Estuary. Due to the influence of human activities, the Pearl River Estuarywith frequently eutrophication can provide a good living environment for anammoxbacteria. Therefore, in order to study the spatial and temporal distribution ofanammox in the Pearl River Estuary, in this study ladderane core lipids in thesuspended particles, surface sediments and three sediment cores have been detectedand compared with the content of dissolved oxygen, ammonium, nitrite and totalorganic carbon (TOC) for revealing its factors.Firstly, the detection of ladderane lipids in all the suspended particles and surfacesediments suggested the widespread occurrence of the anammox in the Pearl RiverEstuary. The spatial distribution of the ladderane lipids in the water column wassimilar to the dissolved oxygen and nitrite, suggesting low dissolved oxygen and highvalue of nitrite may be a necessary factor. But the difference between ladderane lipidsand ammonium suggested that the content of ammonium was not a limiting factor forthe anammox. The high values in the water column of the upstream of Humen andwithin LingDing Yang suggested a stronger anammox, and the anammox activity inbottom water was stronger than the surface water. The different distribution ofladderane lipids and anammox bacteria indicated the source of ladderane lipids may be different in the surface sediment. The ladderane lipids in the upstream of Humenwere mainly produced by the settling of the bottom water column, but in the outsideLing Ding Yang it was mainly produced by the sediment itself. Anammox bacterialdominant genus in surface sediment changed from “Candidatus Brocadia” or“Candidatus Kuenenia” to “Candidatus Scalindua” along the salinity gradient fromfreshwater to the open ocean. The weak correlation of ladderane lipids and TOC alsosuggested the ladderane lipids in the surface sediment were not produced by thesediments self.Furthermore, in order to reveal the past anammox of the Pearl River Estuary, wealso analyzed the content of ladderane core lipids of three sediment cores from thePearl River Estuary. The results suggested that the anammox of the Pearl RiverEstuary indicated the evident geographical distribution of the upstream estuarystronger than the seaside area. The reconstruct of past anammox in the Pear RiverEstuary revealed that at site P03anammox activity had a slowly increasing trend in1970s-1990s and at site L1it had a similar trend over the last decade, but at site C2Tit showed a rapid increase in recent years. This could be because the increased humanactivities bring more and more nutrients influx, and the frequently eutrophication alsoenhanced the productivity. While the respiration of plankton and decomposition of theorganic matter lead to severe oxygen depletion, it also provide a well livingenvironment for anammox bacteria. The vertical distribution of ladderane lipidsindicated that the source of anammox bacteria may be different in the three sedimentscores. Ladderane lipids at site P03were possible mainly produced by the anammox ofthe sediment itself, but at site L1they maybe come from both the sediment itself andthe settling of the above water column, and at site C2T the anammox process mayonly occur in the anoxia bottom water. The correlation analysis between TOC and thesummed ladderane core lipids found that the high abundance of TOC had bettercorrelation, showing that the sediment of containing more organic carbon may havestronger anammox activity.