Study On Phosphorus Forms, Adsorption And Release Risk In Sediments Of Huixian Wetland, Guilin

Phosphorus in water is an important factor of eutrophication.In this study,8representative samples from the Huixian karst wetland in Guangxi were collected for research.Based on basic physical and chemical properties of wetland sediments and overlying water,the eutrophication of overlying water was assessed by trophic level index?TLI?and grey clustering methods.The distribution characteristics of phosphorus forms in different depths sediments were studied,and the adsorption and desorption characteristics of phosphorus by surface sediments were compared under different environmental factors.The phosphorus pollution risk and release risk of surface sediments were evaluated by single factor standard index and phosphorus release risk index?ERI?methods.The following conclusions were obtained through research:?1?In Huixian wetland,except for GSL,whose overlying water quality has reached Grade IV,the other samples are all V or inferior V.The eutrophication level of the overlying water is between light to medium.The total phosphorus content of sediments is 531.31¹322.385 mg/kg,and the organic matter mass fraction is3.22%⁸.18%,average content is 6.80%.The main minerals in surface sediments are quartz,calcite and a small amount of kaolinite,and the main chemical elements are Ca,Si,Fe and Al.?2?Inorganic phosphorus?IP?is the main part of total phosphorus?TP?in sediments of Huixian wetland,accounting for 75.8%⁸5.06%of total phosphorus in sediments.Occluded phosphorus?Or-P?is the main part of inorganic phosphorus,which accounts for 26.64%⁵8.70%of total phosphorus.Iron-bound phosphorus?Fe-P?and organic phosphorus?OP?are the main forms of bioavailable phosphorus?BP?,the BP content of QX point is as high as 286.92 mg/kg⁹80.84 mg/kg,accounting for48.77%to 61.06%of total phosphorus,and which is the highest among the 8 sampling points.Correlation analysis showed that the phosphorus in the overlying water of Huixian wetland was mainly BP from 0-15 cm sediment,and Fe-P was its main source;the correlation between total phosphorus and other forms of phosphorus in sediment was not obvious.?3?The fast adsorption stage of phosphorus in the sediments of Huixian wetland is mainly within the first 0.5 h,and the adsorption amount accounts for 86.58%of the total adsorption.The kinetic fitting results accord with the quasi-second-order kinetic equation.According to the thermodynamic fitting results,the Langmuir adsorption model can well fit the isothermal adsorption of phosphorus in the sediments of Huixian wetland,and the adsorption amount increases with the increase of temperature.The adsorption capacity in acidic environment is higher than that in alkaline environment.?4?Except LSD,LSM and GSL,the total phosphorus standard index of sediments in other sampling points is all higher than 1,which means the high pollution risk to overlying water.The PSI value is 21.053⁴7.803[mgP?100 g?^-1][?mol/L]^-1,which belongs to the lower level,and shows the weak buffering capacity of phosphorus.The content of Fe_ox and Al_ox is lower than that of other lake wetlands,indicating that the active sites of phosphorus adsorption on the surface are less in the sediments.The ERI index is greater than 25%except for GSL,and the release risk of phosphorus from sediments is greater.