Phosphorus Distribution Characteristics Of Sediments-Macrophytes-Water Systems Of Mudong Lake In Huixian Karst Wetland

This paper takes Mudong Lake,Huixian Karst Wetland,Guilin City,China as the research area,and collects three kinds of typical wetland plants,their root sediments and overlying water samples from Cladium chinense,Phragmites australis and Jussiaea repens.Seven-step continuous extraction method was used to extract different forms of phosphorus from sediments.The seasonal variation characteristics of C,N,and P contents in wetland plants were studied.The occurrence characteristics and influencing factors of phosphorus in wetland sediments are discussed.In turn,the relationship between them and the phosphorus interface process in wetland sediments has been studied.The relationship between the physicochemical factors of sediments and the distribution and transformation of phosphorus species was analyzed.In order to further understand the distribution of phosphorus and the characteristics of sediment adsorption on phosphorus in wetlands.The main findings are as follows:?1?The pH value of water in the overlying lake of Mudong Lake is weakly alkaline,ranging from 7.30⁷.60.The TP content in the water is between 0.08⁰.19 mg·L^-1.The TP content in winter and summer waters is high.The content is relatively low in autumn.The TOC,N,and P contents of the three dominant plants,Cladium chinense,Phragmites australis,and Jussiaea repens,ranged from 28.78%⁵3.00%,0.82%².67%,and 0.08%⁰.39%,respectively.In addition,the differences in TOC,N and P contents among plants were extremely significant.The differences in TOC and P content were extremely significant between seasons.The differences in C/N,C/P and N/P between plants were extremely significant.Only differences in N/P were significant between seasons.?2?The content of total phosphorus in the sediments of Mudong Lake is 453.45¹256.87 mg·kg^-1.There is no significant difference between plants and seasons.The content of all forms of phosphorus in the sediments showed ACa-P>Or-P>Fe-P>De-P>Ex-P>Al-P>Oc-P.In the vertical direction,the contents of TP,Ex-P,Fe-P,and De-P appear to be higher?0⁵ cm?in the surface layer of the sediment than in the bottom layer?5²0 cm?.The biologically available phosphorus content of sediments was 81.2²95.0 mg·kg^-1,accounting for 13.3%³1.2%of the TP content of sediments.Correlation analysis showed that there was a very significant correlation between TP and OM,Ex-P,Fe-P,De-P,and Or-P,indicating that TP content reflects the potential release of phosphorus in sediments to a certain extent.Effective control of TP content can reduce the risk of phosphorus release from wetland sediments.?3?Phosphate adsorption kinetics experiments show that the adsorption and release process of sediment phosphorus includes rapid adsorption?0^l h?,slow adsorption?l²4 h?and equilibrium?24⁷2 h?.And the differences in vegetation types have no significant effect on this trend.48 h as the equilibrium time for isothermal adsorption experiments.The Langmuir model fitting isotherm adsorption process showed that the maximum adsorption capacity(Q_max)of the sediments in the study area was between 381.9⁵22.7 mg·kg^-11 and the background adsorbed phosphorus?NAP?was between 4.67⁶7.1 mg·kg^-1.The equilibrium concentration of adsorption and desorption?EPC₀?ranged from 0.009⁰.107 mg·L^-1.The Q_max,NAP and EPC₀ of sediments in the study area were affected by the contents of Eh,TIP and Or-P,and NAP and EPC₀ were also affected by pH.