【作者】 班凤梅；

【导师】 潘根兴； 谭明；

【作者基本信息】 南京农业大学 ， 土壤学， 2007， 博士

【摘要】 石笋作为高分率气候指标的记录体,因其自身的诸多优势,在古气候、古环境重建研究中发挥着重要作用。但其形成机制及其与土壤过程之间的联系研究相对薄弱。本论文通过对石花洞洞穴滴水温度、电导率、pH、主要离子、可溶性有机碳（DOC）等物理化学指标,以及上覆土壤环境和洞穴空气指标近3年的观测分析,对洞穴滴水水化学变化及其沉积过程与上覆土壤的关系进行了研究,获得如下主要结论:1.土壤温度、湿度和CO₂浓度在雨季（7-8月）均达到最高,旱季12-1月最低;土壤CO₂浓度与土壤温度呈指数正相关,而与土壤湿度呈线性正相关;随着土壤深度的增加,土壤温度逐渐降低且趋于平缓,而土壤湿度和CO₂浓度则明显升高;受土壤温湿度条件以及土壤有机质含量的影响,山谷耕地土壤CO₂浓度高于阴坡灌丛土壤。2.土壤DOC在雨季前期最高,经降雨淋滤后,雨季后期出现降低;受土壤微生物活性和植物根系分布影响,土层10-30cm的DOC最高;3个土壤样本DOC含量与其总有机碳（TOC）含量空间变化一致,耕地土壤＞灌丛土壤＞阳坡土壤。3.洞穴滴水主要来自于地表降水,滴率变化对降雨存在3种响应关系:快速响应、滞后响应和稳定响应。快速响应型滴水主要以与地表连通性较好的裂隙或管道补给;滞后型滴水为管道和大面积裂隙双重补给;稳定型滴水仅响应高频低强的降雨事件,主要以基质流或渗流水补给。4.观测点滴水水化学均表现出明显的季节性变化。雨季,随滴率的增加,水流溶解土壤CO₂以及SO₄^2-量增加,滴水pH出现明显降低,稀释作用使快速响应降水的滴水HCO₃^-略有降低;而滴水Ca²⁺、Mg²⁺和Si浓度及EC均出现不同程度的升高,响应降雨越快的滴水点,变化幅度越明显;滴水Mg/Ca和Si/Ca均旱季高于雨季,二者随Ca²⁺浓度的变化趋势符合CaCO₃沉积模拟曲线,表明滴水在旱季存在明显的CaCO₃优先沉积过程。5.滴水方解石饱和指数（Saturation indice for calcite,简称SIc）和沉积量的观测均表明,滴水旱季沉积速率高于雨季,且观测点滴水SIc与滴率呈显著的指数负相关;另外,洞穴温度、湿度和CO₂浓度也可对沉积速率产生影响。6.滴水中DOC含量与土壤DOC变化特点较为一致,雨季出现明显的脉冲峰;降雨强度是滴水DOC脉冲的开关之一,而不同年份降雨的频率和强度差异是DOC年际变化的主要原因,雨季初期高频低强度的降雨易于滴水DOC浓度峰的形成;不同滴水点洞穴顶板厚度、水动力差异引起滴水DOC浓度变化明显不同,顶板较厚且响应降雨慢的滴水DOC浓度可能出现多年一峰,而顶板薄响应降雨快的滴水点表现出一年一个主峰、并伴有多个亚峰的DOC变化特点。本研究表明石花洞土壤CO₂及其地球化学过程对滴水水化学性质变化起着重要的控制作用,进而影响到石笋微层亮、暗层的形成时间及变化特征,初步阐明石笋年层的亮层（方解石层）形成于旱季,暗层（有机质界面层）形成于雨季;石笋微层有机质含量的变化可反映土壤DOC变化及输出特点。更多还原

【Abstract】 In recent years there has been increasing interest in the study of cave stalagmites because of its some unique advantages of being archives of palaeoclimate and palaeoenvionment.In this study,parameters of drip water geochemistry（including temperature,electrical conductance（EC）,pH,main ions and dissolved organic carbon （DOC））,soil environment overlying cave（including temperature,humidity and CO₂ concentration of soil air） and cave air（including temperature,relative humidity and CO₂ concentration） have been monitored over the past 3 years to understand the mechanisms of formation of stalagmites and the relationship of stalagmites growth with soil processes in Shihua Cave.A number of conclusions have been achieved as shown below.1) The temperature,humidity and CO₂ concentration of soil air are highest in July or August（rainy season） and lowest in December or January（dry season）.It has been observed that CO₂ concentration is exponentially correlated with temperature and linearly correlated with humidity.With the increase of the depth of soil section, temperature of soil air decreases,but humidity increases.The CO₂ concentration of cultivated soil in valley is higher than shrub-covered soil on the slope of hill.2) The highest value of soil DOC occurred at the beginning of rainy season. Afterwards,it shows a decresing trend due to the rain leaching.The higher value of DOC is distributed in the soil profile between 10cm and 30cm from the surface associated with the microbial activities and plant roots.The valley has the maximal concentration of soil DOC,followed by shrub-covered soil,and the discontinuous soil between bedrocks has the lowest one. 3) Dripwater in Shihua Cave comes from surface flow.Drip discharges show three types of response to surface flow variations:1) rapid response,2) time-lag response and 3) stable response,which are related to different flow routes of recharge.For rapid reponse,the drip discharge is recharged through the flow routes with intensive fractures and interconnectivities;for time-lag response,the drip discharge is recharged by double-porosity system composed of a high conductivity,low storage capability conduit network and a low-conductivity high-storage capability rock matrix under variable boundary conditions;for stable response,the drip discharge is mainly recharged by seepage flow and base flow.4) Dripwater in all studied sites shows clearly seasonal variations in hydrochemical parameters.During the rainy period,pH is lower because the rain water dissolves more CO₂ and SO₄^2- than dry period.On the contrary,concentrations of Ca²⁺,Mg²⁺, Si and EC increase in rainy season and the more rapid response of the drip water to the recharge,the higher degree of the increase.In addition,Mg/Ca and Si/Ca in drip sites are higher during dry period than rainy season.The trends of Mg/Ca and Si/Ca with Ca²⁺ concentration are consistent with the results of the prior calcite precipitation model,suggesting that there is a process of prior calcite precipitation in the recharge of drip sites during dry period.5) The saturation index of cacite（Sic） of dripwater in all drip sites shows some degree of seasonality.Drip water is more saturated with respect to Ca during the dry period and lower during the rainy period,in agreement with the results of situ calcite growth experiments.It is negatively exponential correlated between the value of SIc and drip rate.In addition,variation in temperature,humidity and CO₂ concentration of interior air within Shihua Cave could affect the calcite growth.6) The content of DOC in drip waters varies inter- and intra-annually and has a significant correlation with discharge of dripwater for the rapid response sites.High DOC was detected in July or August in the three observed years.The flushing of soil organic matter is dominated by the intensity of rain events.The content of DOC was lower and less variable during the dry period than the rainy period.The shape of DOC peak also varies annually as it is influenced by the intensity and frequency of rainfall. Different drip sites show marked differences in DOC response that are dominated by hydrological behaviour linked to the recharge of the soil and karst micro-fissure/porosity network.It has been demonstrated in this study that the sharp peak of DOC in drip water during the rain period corresponds with the formation of the thin and dark layers of the stalagmites,while high Sic in the dripwater during the dry period corresponds with the formation of calcite layer.The variation of DOC content in drip waters,in the mean time,reflects the changes of the origination and transport of DOC in soil.更多还原