喀斯特岩溶裂隙对地下径流和氮素垂直渗漏的影响

为了探究水土漏失过程对岩溶裂隙发育形态的响应,采用野外模拟降雨试验,研究了裂隙出露型岩土(XL)、裂隙埋藏型岩土(XM)两种结构形态岩溶裂隙对地下径流及氮素垂直渗漏的影响,并以全土微区(QT)为对照。结果表明:裂隙出露型岩土(XL)、裂隙埋藏型岩土(XM)和全土(QT)3个处理中地下径流对降雨的响应时间表现为XLXMQT,其初始地下径流产流时间分别是29,77,139min,XL和XM初始地下径流产流时间分别比QT减少了79.14%,44.60%;降雨产流阈值分别为20.64,55.06,94.90mm,以QT的降雨产流阈值为基准,XL和XM的降雨产流阈值分别减少了78.25%,41.98%;地下径流达到稳定的时间分别为59,107,169min,稳定径流速率分别为42.09,42.36,38.24mm/h。不同结构形态岩溶裂隙下XL全氮、硝态氮渗漏浓度最高,浓度均值分别为11.64,10.45mg/L,除XM外,XL、QT在降雨结束前地下径流中的全氮、硝态氮浓度基本达到稳定;不同结构形态岩溶裂隙下全氮渗漏量表现为XLXMQT,硝态氮渗漏量表现为XMXLQT,地下径流中氮素输出的主要形式为硝态氮,其比例约占全氮渗漏量的82.32%~90.12%,而铵态氮渗漏量占全氮渗漏量的比例不足2%。裂隙的存在,尤其是出露地表裂隙的存在,增加了微区底部单位面积土壤地下径流速率,同时还增加了微区底部单位面积土壤氮素渗漏量,喀斯特地区普遍存在的裂隙结构促进了水分入渗,加剧了地下径流中氮素的渗漏。本研究相关结果可为喀斯特地区水土漏失机制的探索以及物质迁移模型的构建提供科学依据。

Effects of Karst Fissures on Subsurface Runoff and Nitrogen Vertical Leaching

To explore the responses of soil and water loss to the development of karst fissures,the effects of two different karst fissures structures:fissures exposed rock-soil (XL) and fissures buried rock-soil (XM) on subsurface runoff and nitrogen leaching were studied through rainfall simulation experiments,in which soil experimental micro-plots (QT) were selected as control.The results showed that the responses time of subsurface runoff under different karst fissures structures listed in the order of XL＜XM＜QT,the responses time of subsurface runoff to the rainfall were 29,77,and 139 min,respectively,and responses time of subsurface runoff of XL and XM reduced by 79.14％ and 44.60％ compared to QT,respectively.The rainfall thresholds were 20.64,55.06,and 94.90 mm,respectively,and rainfall threshold of XL and XM reduced by 78.25％ and 41.98％ compared to QT,respectively.The times of the stability of subsurface runoff rate were 59,107,and 169 min,and the stability of subsurface runoff rates were 42.09,42.36,and 38.24 mm/h,respectively.The nitrate nitrogen and nitrogen concentration were the highest in XL,which could reach 11.64,10.45 mg/L,respectively.The nutrient concentration in subsurface runoff reached a stable value in XL and QT prior to runoff stopped.The total nitrogen amount under different karst fissures structures followed the order of XL＞XM＞QT,nitrate nitrogen leaching listed in the order of XM＞XL＞QT.Under different karst fissures structures,nitrate nitrogen was the main component of nitrogen leaching,which accounted for 82.32％ ～90.12％ in total nitrogen leaching amount,however,the proportion of ammonia nitrogen was less than 2％.The existence of the fissures,especially the existence of the XL,could enhance both the subsurface runoff rate and the leaching of nitrogen for per unit area soil,the soil which at the bottom of the experimental micro-plot.Because of the widely developed fissures in karst region,the infiltration of water was promoted,moreover,the leaching of nitrogen was intensified too.The relevant results can provide scientific basis for explore the mechanisms of soil and water loss as well as construction material migration model in karst region.