Preliminary Investigation Of The Effect Of Rock Surface Litter On The Dolomite Corrosion In Shibing Karst Area

The fragility of karst ecological environment has attracted the attention and research of more and more scholars at home and abroad.With the development of the study of karst ecosystem,the role of biology in karst development has been paid more and more attention.At present,there are more researches on the corrosion effect of moss,lichen and microorganism,and less research on the dissolution effect of higher plants.This study applied grasp the world natural heritage site of dolomite karst as the research area,with the five kinds of forest litter?Evergreen broad-leaved forest,Eeciduous and evergreen broad leaved forest,Mixed coniferous broad leaved forest,Durisilvae and Coniferous forest?as the research object,through field sampling and laboratory analysis,the water holding capacity and water holding characteristics of different forest types were analyzed.The effect of different forest litter on the water performance of dolomite was revealed by the experiment of water holding and water evaporation about different types of litter.Through field monitoring to comparing the differences of the microclimate of the rock table covered by different types of litter and the non-litter coverage,the improvement of the microclimate of the rock surface with different types of rock surface is discussed.Through the above research,it has been preliminarily revealed that different types of rock surface debris have played an indirect catalytic role in carbonate karst erosion.The conclusions are as follows.?1?There is a large difference in the reserves of five types of forest,coniferous forest and sclerophyllum are more abundant in both semi-decomposed and undecomposed layers than mixed coniferous broad leaved forest?Eeciduous and evergreen broad leaved forest?Evergreen broad-leaved forest,the Evergreen broad-leaved forest and Eeciduous and evergreen broad leaved forest have less reserve and the reserve of the mixed coniferous broad leaved forest is in the middle.The maximum amount of water in both Durisilvae and Coniferous forest is similar,it is larger than Evergreen broad-leaved forest,Eeciduous and evergreen broad leaved forest and mixed coniferous broad leaved forest.The maximum moisture content of the litter is related to the reserves of the litter,and the larger the reserves,the larger the maximum amount of water.The maximum water-holding capacity of the five types of forest is greater than that of the undecomposed layer,the water-holding capacity of the semi-decomposed layer is higher,and the water-holding capacity of the undecomposed layer is lower.The natural moisture content of Coniferous forest is the smallest,the maximum retaining quantity and the effective holding capacity are the largest,and then the Durisilvae and mixed coniferous broad leaved forest.The natural moisture content of Evergreen broad-leaved forest and Eeciduous and evergreen broad leaved forest is highest,but the maximum retention and effective retention are lower than the Coniferous forest,Durisilvae and mixed coniferous broad leaved forest.The water content and water holding rate of the five types of forest were increased in logarithmic function with the increase of soaking time,and the water absorption rate decreased as the immersion time increased with power function.In the dolomite karst ecosystem,the greater the litter reserves of each forest type vegetation,the higher the content of organic carbon and CO₂ in the humus produced by its decomposition.The chemical properties of precipitation have undergone great changes after successively leaching litter layers and soil layers.The contents of carbonic acid and organic acids have risen greatly.The soluble salts in water have increased and the pH value has decreased,thus the ability of eroding the bedrock dolomite is greatly enhanced.?2?The water loss of the five samples with litter coverage is much larger than that of the individual dolomite samples,among them,the most significant difference was Evergreen broad-leaved forest,which water loss reached 11.1 times of the sample of individual rocks,and the lowest difference is the Coniferous forest,which is 4.9 times of the individual rock sample.From high to low,Evergreen broad-leaved forest>Eeciduous and evergreen broad leaved forest>Durisilvae mixed coniferous broad leaved forest>Coniferous forest.The Evaporation rate of water loss is as follow,Coniferous forest?70%?,mixed coniferous broad leaved forest?83%?,Evergreen broad-leaved forest?86%?,Eeciduous and evergreen broad leaved forest?90%?and Durisilvae?90%?.The five samples with litter coverage increased 3.9 to 7.3 times more than the individual rock samples.In addition,in 5 types of forest,Coniferous forest can maintain a higher proportion of water.Through further analysis,it can be concluded that after rain,the dolomite can maintain a layer of water film under the cover of litter,and when it is relatively dry,dolomite covered with litter can directly absorb some water from the air.This has greatly increased the water holding capacity of the rock,prolonged the interaction time of the water and rock,and thus promoted the dissolution of the exposed dolostone surface to some extent.?3?The daily variation law of surface temperature of different forest types is consistent,the time of the maximum and minimum temperature is the same,the maximum time is 12 noon,the lowest is 8 o'clock in the morning.In general,the temperature of A layer is significantly higher than that of B layer,it means that the temperature near the litter layer is lower than the surrounding temperature,and the most significant time period is 12 noon.Compared with the rock mass covered with litter,the temperature difference between A layer and B layer is the largest in the area of bare rock,it is higher than the temperature difference of five types of forest.The maximum humidity is 8 o'clock,and the minimum is 12 noon,according to the measurement data,the moisture content measured at each point of the litter was significantly higher than that of the bare rock.The CO₂ fluxes in the near surface layer are:0.83umol/m²/s?coniferous forest type?>0.67umol/m²/s?evergreen deciduous broad-leaved mixed forest?>0.58umol/m²/s?evergreen broad-leaved forest?>0.45umol/m²/s?stonyy forest?>0.43umol/m²/s?Coniferous and broad-leaved mixed forest?>0.18umol/m²/s?bare dolomite surface?,the CO₂ fluxes of the five forest types are greater than the bare dolomite surface.Therefore,it can be seen that the coverage of litters improves the surface microenvironment of dolomite by adjusting the surface temperature and humidity of dolomite,which is beneficial to the biological growth and metabolism of the micro-ecosystem of the rock surface,and accelerates the biological respiration producing a large amount of CO₂;at the same time,litters also produce a large amount of CO₂ during the microbial degradation process,thus increasing the exchange and exchange rates of CO₂ between the rock surface and the atmosphere,and ultimately greatly enhancing the dissolution of dolomite.At the same time,litters also produce a large amount of CO₂ during the microbial degradation process,thus increasing the exchange and exchange rates of CO₂ between the rock surface and the atmosphere,and ultimately greatly enhancing the dissolution of dolomite.