Typical Study On Karst Processes And Elemental Migration In Ecological Environments In Fengcong Stone Mountains

Fengcong stone mountain environments in the karst areas of southwest China,about 500,000 km² , are very fragile. Now Chinese governments face up to theproblems to stop the deforestation tendency, rebuild forest environments and helpthe local people take off poverty. This paper picked up some typical areas, such asNongla in Mashan county, the karst experimental site in Guilin, Shidie in Xinchengcounty, Guangxi autonomous region and Puding, Maolan in Guizhou province, forfield investigations, surveys and collecting samples for experimental analyses in thelaboratory. On the basis of former research results and by means of the systematicanalysis, the karst processes, elemental migration law and the ecological effectsin the fengcong karst areas are approached.The humid and warm monsoon climate and the carbonate rock uplift make thefengcong stone moutain system far away from equilibrium. So there usually arestrong karst processes in the CO₂-water-carbonate rock system. Passing through afengcong depression system, the rainwater with low Ca²⁺ content(less than 5mg/l) becomes rich in Ca²⁺ up to 70-110 mg/l only in Several hours. The solutionrate in Guilin fengcong area is 91.21 m³/km²Â·a. Such rapid and strong solutionprocesses not only promote the formation of both deep epikarst zone and themacroscopic tower or cone stone peak landforms, but also result in the rare soil andbare rocks. However, the solution rate is different in different geomorphologicpositions, hydrodynamic zones and ecological environments. For differentgeomorphologic positions, there is the highest solution rate on the bottom ofdepression, the second highest in the saddle between peaks, the third highest on the top of peaks and the lowest on the steep slope of peaks. For differenthydrodynamic zones, the solution rate is high in the epikarst of vadose zone andgoes down quickly with increase of depth. The karst processes in saturation zoneoccur in the rock near flow water in karst conduit. The quiet water only can lead aweak solution process. The evident differential solution is very important forChinese marvellous fengcong karst landforms. It is also a key factor to understandthe development and evolution of the fengcong stone mountains.The cycle of CO₂-water-calcium in the karst dynamic system can drive theelement migration of the karst environments. Under the strong karst dynamicconditions, a forward element migration happens with dissolution of the carbonaterocks, and the temporary hardness of the karst spring water usually is 11-15 Germandegree. But under the dense forest at Nongla, the highest temporary hardness canreach up to 18.9 German degree, and the insoluble Fe, Si, Al, P and Mn can also bepartly dissolved into karst water. If some carbon dioxide escapes from the karst water,a backward element migration happens with the deposition of calcium carbonate.With the element migration, the fengcong karst areas become calcium-rich and a littlealkaline geochemical environments. For example, there are calcareous soil which itschemical composition has a close relation with the karst processes, high hardnesskarst water, and enriched calcium trees.The geochemical background of rocks has an important role in the elementmigration of the environments. In dolomite areas, there is a complete soil profilestructure(from D, C, B to A) on the gentle slope of mountain. And below B layer,there is a general law that main consituents and some trace elements increase with thedepth, which show that the soil is the monochronogenous soil and is leached andweathered gradually. However, no C layer and the gradual change law of elements isin the limestone soil profiles. There are relative abundant background value of traceelements in the argillaceous and silicaeous dolomite of the Donggangling Group ofDevonia in Nongla, which, with element migration, results in the relative highmineral nutritious elements in water, soil and vegetation.The special element migration law in fengcong stone mountains results in thekarst geological ecology. The vegetation is characterized by calciphile, xerophyte andlithophyte. And the species is quite different in different geological regions. Somespecial karst areas, such as Nongla in Guangxi, have enough mineral nutritiouselements for promoting development of species diversity. There are a lot of good fruits and precious herbs in Nongla, which help the local people take off their poverty.