Research On Epi-Hydrogeochemi-Cal Of Secondary Forest In Southeast Yunnan Peak Forest-lake Basin

In order to explore the Epi-hydrogeochemical of secondary forest in Southeast Yunnan Peak Forest-lake Basin,to evaluate the‘autotrophic regulation’ability of the micro-habitats,to reveal the restoration status of the structural functional layer of the Epi-karst ecological system.By means of hydrological observation and comprehend-sive research method of water chemical tracer,the Epi-hydrogeochemical were obser-ved synchronously in different niches of the secondary forest in the Southeast Yunnan Peak Forest-lake Basin.This paper studies the physical and chemical characteristics of various levels of water in the process of atmospheric rainfall flowing through the vegetation-litter,layer-soil,Epi-karst spring and the change mechanism,the nutrient return amount of litter decomposition rate in different habitats,and the spatial hete-rogeneity of soil nutrients.The results are as follows:（1）Studies on physical and chemical characteristics of atmospheric rainfall and rainfall components in secondary forest show that:Vegetation has a significant effect on the physicochemical properties of atmospheric rainfall,soil water,and Epi-karst spring water;and the vertical spatial distribution of rainwater physicochemical pro-perties is significantly different.The associated ions that flow with rainfall follow the‘atmospheric-forest-surface runoff-subsurface runoff’trajectory and some ion con-centrations are‘enriched’or‘discrete’.According to its vertical change in space,it can be divided into 3 types:Sustained enrichment type,including Ca²⁺,Mg²⁺,sur-face enrichment type,including K⁺,NO₃^-,NH₄⁺,and other types including PO₄^3-.The associated ion amount of net increase of secondary forests per year is 142.29 kg/（hm²·a）.Among them,K⁺,Ca²⁺,Mg²⁺account for 0.21⁰.34%,0.28¹.25%,0.01⁰.23%of the total forest‘vegetation-soil’system,respectively.This shows that the functional layer of the water-bearing structure in the Epi-karst of the secondary forest in the study area is relatively complete,during the restoration of the secondary forest,the nutrient supply of the surface karst ecosystem can be increased by precipitation.（2）According to heterogeneity analysis of soil nutrients in different microhabitats of secondary forests,it shows that the soil temperatures of rock gully,slopes are reduced during the rainy season and increased during the dry season,however,the pH,EC,exchangeable Mg,exchangeable Ca and K characteristics of the soil shows opposite trends under the same conditions.This analysis reveals the heterogeneity of soil nutrients that annual average value of rock gully is higher than that of the slope.On the basis of differences in physicochemical properties of different soil layers in the microhabitats,it indicates that the difference of nutrient in soil of rock gully,slopes between 0²0cm,20⁵0cm and 50⁸0cm is the most significant.Ca²⁺and Mg²⁺are the maximum of ion concentration in surface runoff of Epi-karst ecological system which is arranged in descending order as Ca²⁺>Mg²⁺>K⁺>NH₄⁺>NO₃^->PO₄^3-.The concentrations of ions in the soil water are Ca²⁺>NO₃^->Mg²⁺>K⁺>NH₄⁺>PO₄^3-in which Ca²⁺,NO^3-and Mg²⁺are the most concentrated.Ca²⁺,Mg²⁺,K⁺,NH⁴⁺,NO^3-,and PO₄^3-in surface runoff water is higher than that in soil water in the rainy season.Fluxes in surface runoff and soil water are all negative except that the NO^3-flux difference is positive.That indicates the water flowing with surface runoff has the effects of static dissolution and elution on PO₄^3-,Ca²⁺,Mg²⁺,K⁺,and NH₄⁺.（3）The study on nutrient release of the litter in different habitats of secondary forest shows that the amount of litter in soil slope is the largest（16.98 t/hm²）and the release dynamics of rock gully,soil slope and stone surface are released the fastest during the rainy season which the rate of release is slopes>stone surface>rock gully.However,there are significant differences in the elements flux of the decomposition and release of different habitats which the elements flux is organic carbon>N>Ca>Mg>K>P.The elements flux of organic carbon,N,Ca and Mg is the soil slope>rock gully>stone surface and the elements flux P,K the soil slope>stone surface>rock gully.The study on the spatial heterogeneity and the nutrient release of litter in the soil of the microhabitats shows that the differences in the restoration of soil slope,rock gully and stone surface,and the Epi-karst ecological system of soil slope and rock gully is recovered better.It is indicated that the recovery of the vegetation layer in the secondary forest can promote the restoration of the water structure functional layer of Epi-karst ecological system and enhance the ability of‘Autotrophic regulation’.