岩溶流域不同土壤剖面溶解性碳氮分布和淋失特征

Distribution and Leaching of Dissolved Carbon and Nitrogen in Different Soil Profiles in Karst Basin

选取了重庆青木关岩溶流域不同土壤剖面,按10 cm间隔取样,测试各种土壤溶解碳氮含量,探讨不同土壤剖面溶解碳氮分布和淋失特征。结果表明,岩溶流域不同地质背景、植被类型和土地利用方式下的土壤剖面溶解碳氮均具有横向和垂向差异。砂岩区林地土壤DOC、DON和铵态氮含量高于灰岩区的土壤,而其硝态氮含量比灰岩区土壤低。灰岩区土壤DOC和DON含量为草地≈林地>退耕还林地>灌丛>耕地(稻田除外),它们均随着深度增加而降低。岩溶区土壤DOC和DON与土壤pH值成反比,受富钙镁偏碱的岩溶生态环境制约,土壤溶解性有机碳氮会发生中和或螯合反应而被固定。岩溶区特殊的土壤剖面结构使得土壤DOC和DON在降雨条件下存在淋失的可能性。不同土壤剖面溶解无机氮形态以硝态氮为主,其次为铵态氮,亚硝态氮含量较低。林地铵态氮受植被类型影响较小,且低于耕地。不同土壤剖面硝态氮含量为耕地土>灌丛土>退耕还林土>草地土>林地土,其含量均随深度增加而升高,具有累积效应,表明土壤硝态氮发生了淋溶作用,其在降雨条件下极易淋失进入岩溶地下水中。

Soil samples were investigated at 10 cm intervals in different profiles in Qingmuguan karst basin,Chongqing,China.Soil dissolved carbon and nitrogen（organic and inorganic species included） were analyzed to explore the distribution and leaching in different soil profiles.The results show that contents of soil dissolved carbon and nitrogen varied both laterally and vertically in different soil profiles under different geology,vegetation and land use conditions.Forest soils in sandstone area had higher DOC,DON and NH＋4-N contents but lower NO-3-N content than those in limestone area.In limestone area,the mean contents of soil DOC and DON decreased from grassland,coniferous forest land,afforestation land,shrub land,to tilt land（except for paddy soil） successively and from surface to bottom in soil profile.Both DOC and DON contents of karst soil were correlated negatively with soil pH value due to the neutralization or sequestration in the karst environment with high pH value,Ca2＋ and Mg2＋ contents.Owing to the special structure of karst soil profile,soil DOC and DON could possibly leach into karst aquifer by rainfall.NO-3-N was the main species of dissolved inorganic nitrogen,followed by NH＋4-N,and NO-2-N was much lower.NH＋4-N content of forest land was lower than that of tilted land and affected less by vegetation types.The mean NO-3-N content declined from tilt land,shrub land,afforestation land,grassland to coniferous forest land successively,but they rose with soil depth increase,showing the cumulative effect,which indicates that the soil nitrate occurred leaching and would be easily carried away into the karst groundwater during rainfall events.