Distribution And Source Analysis Of Carbon And Nitrogen In The Wetland Soil Of Poyang Lake

In this study, the Poyang Lake wetland is the research object. We studied thecarbon and nitrogen content distribution characteristics of types of wetland soil duringthe high water period and low water period and cleared the relationships between thecarbon and nitrogen distribution of wetland soil and the physical and chemical factorsof soil by analyzing the carbon and nitrogen content of types of wetland soil during thehigh water period and low water period and its essential physical and chemicalproperties, with combining the hydrology and seasonal variation characteristics ofwetland. On this basis, thoroughly analyzed and discussed the vertical distributioncharacteristics of organic carbon, nitrogen in the profile of sediment, analyzed thecontent of organic carbon, nitrogen, characteristics, sources and evolution process ofPoyang Lake in different historical period, revealed that series of changes of theorganic matters in Poyang Lake internal environment. All we did can provide certaintheoretical basis for regional carbon and nitrogen cycle study.Study received the following valuable results:(1) In high water period, the main type of wetland is water, overall area is around2778.22km2；In low-water period, mainly in the carex wetland, overall area is around is828.84km2. In high-water and low-water period, the difference between soil physicaland chemical properties of different wetland, and the temperature, moisture contentand Eh difference are obvious, while the pH were similar. The vegetation communitiesof the different type of wetland is different too. The vegetation communities isPotamogeton malaianus--Vallisneria+Hydrilla in water type, the vegetation communities is Potamogeton malaianus--Vallisneria in mud type; the vegetationcommunities is sedge+Chinese Cinquefoil Herb in sedge type and the vegetationcommunities is Phragmites-sedge-Potentilla tanacetifolia in Phragmites type.(2) The total carbon content of Poyang Lake wetland’s surface soil is in the rangeof1.6~32.7g/kg, and the total nitrogen content is in the range of0.08~0.08g/kg.Variation characteristics of C and N content in soil is mainly manifested in thevariation in content of organic carbon, and nitrogen, whose characteristics are high inwet reason and low in dry season. The content of TC in the wet and dry season iscarex> reeds> mudflats> waters while that of TN is reeds> carex> mudflats>waters. The peak of the content of organic carbon and nitrogen value appears in dryseason, and the organic carbon mass fraction in carex type wetland up to14.36g/kgwhile the organic nitrogen mass fraction up to1.47g/kg. Through the analyses of thecontent of C and N, physical and chemical properties of soil and the relationshipbetween the vegetation, the main factors that influencing the content of C and N in soilare the change of physical-chemical property of soil (temperature, moisture contentand Eh value) and growth cycle of wetland vegetation.(3) The trend of change of the physical and chemical characters of the deposits inthe whole profile of the northern Poyang Lake center L1column shows consistent withthat change in the southern Poyang Lake center L2column, and the various indicatorschange marginally. The value of δ13C in the two column sample sediment ranges from25.49‰to20.89‰, the value of δ15N varies between4.00‰and6.00‰, the value oftotal organic C varies between0.34%and1.26%, the TOC value of the two columnsshowed a trend of rising and similar and the value of TN varies from0.03%to0.10%.Through comparative analysis of the two column profile find that the sedimentaryorganic matters in the southern and northern center of the Poyang Lake are mainlyderived from native aquatic organic matters and less affected by terrigenous input. Thesediment profile of L2column changes not obviously. The land matters pollutants havelittle influence on the southern lake. Before the1970s, the nitrogen in the sediment ofthe Poyang Lake L1column was mainly derived from the algae in lakes. From1970sto now, the main sources of the nitrogen in the sediment are still aquatic plantcommunity. But as the growing of the industry and agriculture surrounding the PoyangLake and the input of the exogenous pollutants increasing gradually, the effect on theorganic nitrogen source is increasing. In the early20th century to the1960s and80s,the sediment nitrogen of the L2column mainly came from the deposits of the aquatic plant and the water and soil loss. From1980s till now the main sources of the depositnitrogen in deposits are the lake algae and the input of the exogenous pollutants. Thenitrogen in sediment of L1and L2column is consistent on time scales.