Storage Features Of Soil And Eco-hydrological Effects In Typical Karst Underground Fissures

Erosion and weathering of carbonate rocks would form unique karst landform in the shallow layer of karst area,such as pores,fissures and so on.Some of the pores(fissures)filled with soil well form relatively stable niches,which could provide water and nutrients to support the growth of plants.In this paper,the karst shallow fissures filled with soilwas investigated.Based on field survey,some tipical karst shallow fissures were selected.The soil particle composition,nutrient,water holding capacity and infiltration characteristics were studied through field sampling and laboratory experiments.The typical karst rocky desertification area was selected to study the utilization of karst fissure water by analysing main afforestation plants.Through the research,we could enrich the cognition of the ecological environment in karst area,and offered a reference for revealing factors of plant growth in the fragile karst,especially under the environment conditions of stone,in order to provide the basis for the study of vegetation restoration and soil improvementand to promote the ecological restoration and management in karst area.The main results were as following:(1)The content of clay(<0.002mm)in the vertical section of carbonate rock fissures was 25.60%~76.67%,which in the fractal dimension of soil particles was 2.53~2.86.From the surface to the lower layer,the fractal dimension of dolomite fissures gradually increased,whereas it could also reduce in dolomite fissures.The content of clay was linear with fractal dimension of carbonate rock fissures,that was y=0.006x+2.414,R2=0.908.The soil sand content ofsurface(S)soil was significantly larger than that of underground space(U1,U2 and U3)(p<0.05),and the soil clay content was significantly less(p<0.05),but the soil silt content was no significant difference.There was no significant difference among different layers of underground space(U1,U2 and U3).The coefficient of variation of soil particle composition was relatively large,which reflected the spatial heterogeneity of carbonate rock in different regions.(2)Soil pH of carbonate rock fissures ranged of 6.66~8.50,basically belonged to the neutral and weak alkaline,and soil pH of surface was a little smaller.The range of total nitrogen content in soil was 0.400g/kg ~3.710g/kg and changed remarkably,from the surface to the lower layer,which indicated a downward tendency of total nitrogen content roughly.The range of total phosphorus content in soil was 0.156g/kg ~1.152g/kg.From the surface to the lower layer,it indicated a downward tendency of total nitrogen content roughly in dolomite fissures and it seemed complex in dolomite fissures.The range of total potassium content in soil was 0.561g/kg ~33.771g/kg,whichshowed no significant change.(3)Thesurface(S)soil pH of carbonate fissureswas smaller than that of underground space(U1,U2 and U3).The difference among S,U1 and U2 was not significant,but the difference was significant with U3(P<0.05).Thetotal nitrogen content of S was higher than that of underground space(U1,U2 and U3),and the difference was significant(P<0.05).There was no significant difference among different layers of soil(U1,U2,U3)in the underground space.The total phosphorus of surface(S)soil was higher,butthe potassium content was lower.There was no significant difference among different layers of soil.In the underground space of carbonate rock fissures,the average of soil p H was 7.48,and the average content of total nitrogen was 0.698g/kg,the average content of total phosphorus was 0.588g/kg,the total potassium content was 9.554g/kg.Itbelonged to lack of total nitrogen,total phosphorus and potassium content is relatively suitable,neutral or weak alkaline soil.(4)On the whole,soil maximum moisture capacity of carbonate rock fissures varied between 37.67%~56.35%,soil capillary moisture capacityvaried between 30.18%~49.07%,soil water-holding capacity varied between 28.77%~46.87%,soil water holding capacity had a wide variation range.Compared with the layersof underground(U1,U2 and U3),the soil maximum moisture capacity,soil capillary moisture capacity and soil water-holding capacity of surface(S)was lower than U1 and U2,but was higher than U3.But the difference was not significant.There was no significant difference among different layers of soil.(5)In the tipical carbonate rock fissure,soil maximum moisture capacity,soil capillary moisture capacity and soil water-holding capacity boosted with the increase of content of clay generally,andpresented linear relationships respectively,whose fitted curves were y=0.694x+10.35(R2=0.843)?y=0.619x+9.629(R2=0.867)?y=0.55x+9.989(R2=0.856).(6)There was good effect to simulate the infiltration process of tipical carbonate rock fissures by Kostiakov model,and the average fitting coefficient was 0.913,which was 0.887 in CK sample.Compared with the content of soil sand,the soil-rock interfaces in karst fissures became the infiltration channel of rain more easily.The fissures filled with soil had good effect on infiltration and storage of rain.(7)The annual average precipitation is 858.7mm in recent 16 years near Caohai of Weining country,the maximum annual precipitation was 1313.9mm,and the minimum annual precipitation was 619.3mm.These years belonged to hemiplegia time from the view of hydrological years.The local climate was monsoon.The rainfall stable 18 O showed the characteristics of positive indry season and negative in rainy season,the variation of the fissure spring was small and had certain stability.The soil stable 18 O of Pyracantha was more positive than that of Ligustrum bothin rainy and dry seasons.(8)The most proportion of water utilization was soil water by Ligustrum(60.81%)in rainy seasons and the most proportion of water utilization was fissure water by Pyracantha(44.69%).The most proportion of water utilization was fissure water by Ligustrum(44.74%)in dry season,and the same to Pyracantha(58.23%).The proportion of fissure water utilization increased nearly 30% in dry season by Ligustrum compared with in rainy season,the gap of fissure water utilization had narrowed almost to15% between Ligustrum and Pyracantha in dry season,which had greatly improved than in rainy season.It showed that Ligustrum roots coulduse fissure water well after three years of afforestation,and there was a good effect of ecological restoration whenLigustrum planted.(9)The weight indicator forstorage features of soil and eco-hydrological effects in typical karst underground fissures of soil composition and nutrient characteristics,soil water holding capacity and infiltration characteristics,water use characteristics of plant roots is 0.078,0.287 and0.635 respectively.It should be given to the selection of those plants which had well-developed root system and high utilization efficiency of the karst fissure water during the process of ecological restoration preferentially.In the early stage of ecological restoration,could promote soil nitrogen accumulation in karst shallow fissures improve soil quality,and provide the possibility for ecological restoration of forest.