气象要素及土壤理化性质对不同土地利用方式下冬夏岩溶作用的影响

为揭示岩溶作用对不同人类活动强度土地利用方式、季节变化的响应,在重庆青木关岩溶槽谷区选取地质背景相同的6种典型土地利用方式(旱地,水田,退耕林,荒草地,杉竹混交林,竹林),利用标准溶蚀试片法得到各样点冬、夏两季单位面积溶蚀数据。并用自动气象站降水、气温,各样点土壤水、土壤CO2、土壤有机质、土壤pH、土壤容重、土壤孔隙度等数据对溶蚀结果进行分析。结果是:(1),夏季各样点壤中平均溶蚀量为冬季的3.87倍,且最大溶蚀量从夏季-80cm处上升为冬季-20—-50cm处;(2),受人类活动影响强度大的旱地、水田溶蚀量大于人类活动强度逐渐削弱的退耕林、旱地,而受人类活动影响最小的山竹混交林、竹林溶蚀量最小。且在人类活动强度较大的夏季三者之间差值较大。分析认为:水分、热量与溶蚀的季节变动存较好正相关关系,是影响溶蚀的最基础因素;土壤CO2在降水量大的夏季才能更好地促进溶蚀;土壤有机质与土壤pH反相关,二者协同影响溶蚀,在有机质含量高、pH偏低的表层对溶蚀影响大,其它层位影响较小;土壤容重、土壤孔隙度反映的土壤质地对溶蚀的影响是双向的,偏黏土持水性好而渗透性差,可促进降水少的冬季的溶蚀,如荒草地;砂土则渗透性好而持水性差,对降水多的夏季溶蚀有利,如旱地。另外,农业活动中用到的农家肥、化肥含NO-3、SO2-4,也会促进溶蚀。研究成果可为更科学准确地评估岩溶碳汇效应提供参考。

The influence of meteorological factors and soil physicochemical properties on karst processes in six land-use patterns in summer and winter in a typical karst valley

Many studies showed that the carbon sink resulted from karst process is fast and stable, which compose the very important part of "Missing carbon sink". Different land-use patterns can affect the karst process by influence the soil properties. Commonly, with the land-use change from forest land to cultivated field the soil organic matter will reduce, the stability of soil structure get worse, the soil moisture retaining quality get down and the quantity of soil microbiology will diminish, all the above would affect the karst process.This study took 6 different land-use patterns(Tilled land (code: Ha),Paddy field(St), Reforested land(Tu), Abandoned Land(Hu),Mixed Woodland with Chinese fir-bamboo(Sz) and Bamboo land(Zh))with the same geological backgrounds but different human influence intensity in Qingmuguan karst valley as a case study to determine the influence factors on karst processes. Standard limestone tablets were buried in the field to test the dissolution process rate. HOBO automatic weather station was located in the roof of local people's house to get the precipitation and temperature data. CO₂ content in different soil layers were tested by Gas-Tec CO₂ tester. Soil samples in different layers were taken back to laboratory to detect the pH value, the organic matter, soil moisture content, and soil bulk density.The dissolution data from tablets showed that, firstly, the mean dissolution mass per unit area of different land-use patterns in different layers in Summer were 3.87 times than in Winter. The max mean dissolution mass changed from -80cm layer in Summer to -20--50cm layers in Winter. Secondly, the mean dissolution mass in these two land-use patterns Ha and St with strong human influence intensity (Abbr. HII) was higher than that inTu and Hu in which the HII get weaker, while that in Sz and Zh which had the weakest HII with the lowest mean dissolution mass. Also, the range between them was higher in summer with strong HII than that in winter.Afteranalyzing the temperature(T), precipitation (P) and the soil physicochemical properties data, we can find that, there was a positive correlation between the change of dissolution mass with seasons and T,P which were the most important factors affecting the former. The soil CO₂ content can only play an important role on dissolution in summer which has more precipitation, and these two factors can react each other enough to form more carbonic acid so more carbonate tablets can be dissoluted. There was a negative correlation between soil organic matter and soil pH, and these two factors affected the dissolution jointly. They can influence dissolution greatest only in surface layer with high organic matter and low pH, while less in deeper layers. The influence of soil texture determined by soil bulk density and soil porosity on dissolution was bidirectional. The clay with good moisture retaining quality but bad permeability was benefit for the dissolution in winter for there was less precipitation that time, but bad in summer for there was no so much water pass through the soil, Hu was a good example of this. However, there was an oppose process in sandy soil with good permeability but bad moisture retaining quality, corresponded more dissolution in summer and less in winter, there was a good example of tilled land also. Additionally, the use of farmyard manure and chemical fertilizer which include NO₃^- and SO₄^2- can promote the dissolution process too. Above all, the results of this study can provide consultation for evaluate karst carbon sink more scientifically and accurately.