The Distribution Pattern Of Organic Carbon And The Affecting Factors In The Typical Wetlands In Shandong Province

The greenhouse effect is being a threat to the global environment due to the industrial revolution and large emission of greenhouse gases.Terrestrial ecosystem can absorb atmospheric CO2 by plant photosynthesis and convert it into stable organic matter and then deposit into soils or sediments.Therefore,terrestrial ecosystem is a huge carbon pool.Wetland,as one kind of the terrestrial ecosystem,composes of swamp,peat,fen,and perennial water area,either natural or artificial constructed,either flowing or silent,either freshwater or brackish.Wetland also includes coastal sea with a water depth lower than 6 m.Wetlands hold up to 40%of the organic carbon(OC)budget(?1400 Pg C)globally,despite accounting for just 4-6%of the global land area.Wetlands can be divided into natural wetlands and constructed wetlands,natural wetlands are dominated by rivers,lakes,swamps,etc.Many environment factors may have significant impacts on the carbon deposition in wetland,such as wetland types and soil depths,which can further affect the efficiency of carbon storage.Therefore,the study on carbon distribution pattern and the affecting factors in different wetlands can not only evaluate the carbon deposition in wetlands,but also improve the managing and maintaining strategies effectively and then alleviate greenhouse effect.Organic carbon can be classified into dissolved organic carbon(DOC)and insoluble organic carbon based on the solubility.Insoluble organic carbon can be classified into light fraction organic carbon(LFOC)and heavy fraction organic carbon(HFOC)based on its density.DOC is the organic carbon that can be dissolved into water or neutral salt solution,and the particle size of DOC must be filtered through the 0.45 ?m filter membrane.DOC is refer to the metabolite or intermediate metabolite of microbial and biological residues,and mostly it composes of humic acid and other organic acids,phenols and sugar,etc.LFOC is a sum of OC of undecomposed or decomposed biological residues,and it composes of monosaccharides,polysaccharides,lignin,and other liable structure.HFOC is one stable organic carbon,which in forms of the organic-inorganic compounds,and it is the main component of carbon pool in terrestrial system.The study on the distribution of LFOC and DOC not only can evaluate the proportion of liable organic carbon in wetlands,but also can explore the effect of environmental factors on the carbon stock.The study on the distribution of HFOC can analyze the deposition trend of stable organic carbon.Although the contents of greenhouse gases are in an increasing trend,the study on the distribution of OC and its affecting factors in Chinese wetlands is still not comprehensive.Tuhai River and Majia River system(TR&MR)is one of the three river systems in Haihe River Basin,TR&MR flows through Henan Province,Hebei Province,and Shandong Province,and into Bohai Bay at Binzhou city.Zhaoniu River(ZR),as a tributary of Tuhai River,flows through the industrial districts of Qihe county and Yucheng city,and withstands the pressure of local industrial pollution.Thus,government constructed the Zhaoniu River Constructed Wetland(ZRCW)to purify water from ZR.Nansi Lake(NL),is not associated with TR or MR,is an inland lake.Nansi Lake is located in south of Jining,Shandong Province,is an important reservoir lake in the South to North Water Diversion Project.The Xinxue River(XR)is a tributary flowing from Xuecheng district of Weishan county into NL on the southeast side.For the purification of XR and prevent the water from further polluting NL,the government built the Xinxue River Constructed Wetland(XRCW)in downstream of XR.The carbon distribution,composition and the affecting factors in natural and constructed wetland were analyzed by field study on TR,MR,ZR,ZRCW,XR,XRCW,NLE,and NL.Based on the field sampling and experimental analysis to sediments and shore soils in MR and TR,the results showed that HFOC had no significant difference between sediments and bank soils,or among upstream,midstream,and downstream.The LFOC is higher in upstream than in midstream or downstream of the two rivers.HFOC and LFOC in MR were the highest in downstream and the lowest in midstream.The distribution of HFOC and LFOC in MR or TR had similar trends between sediments and bank soils,and the content of HFOC in sediments was higher than that in the bank soils totally.The study demonstrated that the deposition of OC in wetland sediments is higher than in bank soils.TR and MR,as the same river system and flowing trend,have different distribution pattern of carbon fractions.To further study the distribution pattern of carbon fractions and the affecting factors in natural and constructed wetlands,two researches were conducted by sampling XR,XRCW,ZR and ZRCW twice.It was found that the distribution pattern of HFOC was not affected by wetland types,up/mid/downstream,or depths.The content of LFOC in ZRCW is significantly lower than in other wetlands.The distribution pattern of dissolved organic carbon(DOC)between upstream and downstream or wetland types was not different during the two studies.The significant linear relationship between organic carbon and organic nitrogen indicated that nitrogen content was an important factor restricting carbon accumulation in light groups.The distribution of OC among the seasons showed that the carbon fractions in summer was higher than that in autumn.The distribution of heavy metals(copper,zinc,manganese,cadmium and lead)was higher in downstream than in upstream in XR and XRCW.The contents of cadmium and lead in the surface sediment were significantly higher than those in the subsurface sediments,which were significantly correlated with HFOC.The study showed that the contents of LFOC and DOC can be affected by the environmental factors,whereas HFOC was the main form to deposit organic carbon stably.The distribution of carbon fractions under the invasion of Alternanthera philoxeroides and different microbial richness and diversity have analyzed by sampling the invaded and uninvaded sediments in XR,XRCW,NLE and NL.The results showed that the contents and storage of light fraction organic nitrogen(LFON)and heavy fraction organic nitrogen(HFON)increased significantly under the invasion of A.philoxeroides,whereas the increase in LFOC and HFOC were not significant.Depths had no significant effect on the content of carbon and nitrogen fractions,while LFOC and LFON were significantly higher in constructed wetlands than in natural wetlands.The content of LFOC and LFON in the four studied areas can be sorted as:XRCW>NLE>XR>NL.The storage of HFOC also showed the opposite trend with that of LFOC,and sorted as:NL>XR>XRCW>NL,which was opposite to the storage of LFOC.The distribution and composition of microorganism had no significant difference under the invasion,and three clusters were divided by the cluster analysis of the microbial phyla among the sampling sites.Clusters 1 and 3 were dominated by Actinobacteria and Proteobacteria respectively,which had significantly lower contents of LFOC.The study proved that the contents and storage of carbon and nitrogen fractions can be increased by the plant invasion,while stock of HFOC in natural wetlands was higher than constructed wetlands,and the high microbial diversity and richness can contribute to the accumulation of liable organic carbon.According to the literature search on the distribution of organic carbon in wetland of China,this research found that precipitation was a sensitive factor affecting the distribution of OC.With the increase in precipitation,OC in inland wetlands increased firstly and then decreased and reached the maximum value in precipitation about 800 mm.The distribution of OC in the coast seas(Bohai Sea,Yellow Sea,East Sea,and South Sea)significantly differed from that in inland wetlands,it increased gradually with the decrease in latitude.The distribution and composition of OC and its affecting factors were studied from regional and national scales.Regional study showed that wetland types,up/mid/downstream,depths,seasons,microbial communities,and plant invasion can affect the distribution and composition of OC.Whereas precipitation can affect the distribution of OC in national scale.This research has laid the elementary knowledge for further study on organic carbon at global scale.