| Poyang Lake is an important inflow-and-outflow lake in Yangtze Basin,whose water levels change,and drying rewetting alternates frequently on its beaches.In recent years,influenced by many factors,such as the amount of rainfall and the operation of the Three Gorges Project,the processes of the Poyang beaches flooded or exposed have changed significantly.Meanwhile,the water quality of Poyang deteriorates to some extent,with its nutritional status transiting from trophic to eutrophic.In order to fully figure out how the seasonal changes of the water levels of Poyang influences the amount of endogenous nutrients in wetland,the variation characteristics and other affecting factors of the contents of Nitrogen and Phosphorus in wetland under different water-content conditions.Results are as follow:1,Withdifferentcultured conditions,the most obvious change of soil physical property of Poyang is water content,then is the soil pH.According to the stimulation experiments,compared with the original ones,the soil pH of different cultured groups has increased to some extent.Specific performance: the soil pH of the groups with more water content is slightly higher than that with less water content,and the soil pH of the groups with waterweeds added is higher than that without waterweeds.Moreover,the differences of the contents of Oxygen absorbed by soils of different cultured groups are not obvious: they are at anaerobic conditions.2,The initial value total Nitrogen of wetland soils is 1375-1416mg/kg,and the percentage of organic Nitrogen reaches 90%.Under different cultured conditions,the Ammonia Nitrogen in soils shows an increasing trend.But the increase extent of Ammonia Nitrogen in top soil(0-2cm)is smaller than that in subsoil.As for the Nitrate Nitrogen,no matter in topsoil or subsoil,the contents of Nitrate Nitrogen decline largely,but it is little difference vertically.Among the different cultured groups,the soil total Nitrogen changes significantly in the constant dryness groups and the constant wetness groups.In addition,carex decomposition contributes to the increases of total soil Nitrogen,Ammonia Nitrogen and Nitrate Nitrogen in partial soils.But in cultured groups with carex added,the total soil Nitrogen and the amount of organic Nitrogen in topsoil(0-2cm)are lower than that of the groups without carex.3,The content of the Poyang soil total Phosphorus is 531mg/kg,most Phosphorus combines into Ca-p,and Ca-P is the main component of Poyang wetland soil Phosphorus.The total Phosphorus content influenced by the dry-wet alternation is mainly in topsoil(0-2cm),while that of subsoil has not obvious changed.In the groups with waterweeds in,the soil total Phosphorus increases the most,and the maximum is 650mg/mg,increased by 22%.With dry-wet alternation,the change rule of inorganic Phosphorus and Ca-P is similar with that of the soil total phosphorus.While it is different from that of Fe/Al-P.The content of Fe/Al-P in 0-2cm topsoil in different nutritive conditions is lower than the initial value,especially the 3 groups with waterweeds added,and the largest decline is by 28.7%.4,The initial value of Poyang wetland soil organic Phosphorus is 218mg/kg.Seen as a whole,the change of soil organic Phosphorus concentration is small in the groups without waterweeds.While in the groups with adding waterweeds,the soil organic Phosphorus content presents the tendency of decreasing within 0-2cm of topsoil.However,in subsoil of 2-5cm depth,where the sample waterweeds are added,the soil organic Phosphorus contents increase in varying degrees,and that of groups of dry-wet alternation increases to 248mg/kg,increased by 14.4%.From the perspective of components,the main body of organic Phosphorus are monoester and diester.And in the constant humidity groups and the constant dryness groups,the contents of diester/monoester and the diester/inorganpyphosphate remarkably increases,while with waterweeds added,the contents of diester/monoester and diester/niorganpyphosphate increase sharply too. |
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