青藏高原热融湖塘沉积物理化性质特征

Physicochemical Properties of Sediment of the Thermokarst Lake within Different Vegetation Types on the Qinghai-Tibet Plateau

热融湖塘是多年冻土区常见的地貌,全球气候变暖导致多年冻土退化会加快热融湖塘的形成和扩张,进而会增加多年冻土区碳的释放。热融湖塘沉积物与温室气体释放有着重要的关系,明确其沉积物碳氮含量等理化性质特征有助于认识青藏高原C、N循环对全球气候变化的响应。该研究选择青藏高原中东部116个热融湖塘为研究对象,采集热融湖塘沉积物样品,测定其总碳(TC)、有机碳(OC)、总氮(TN)、pH、沉积物粒径等理化性质,分析TC、OC、TN含量分布特征和各理化性质之间的关系。结果表明,TC、OC、TN含量均为高寒沼泽草甸区>高寒草甸区>高寒草原区>高寒荒漠区,沉积物粒径中粉粒加黏粒含量为高寒沼泽草甸区>高寒草原区>高寒草甸区>高寒荒漠区。研究表明:(1)沉积物TC含量为0.78~110.71 g/kg,OC含量为0.87~85.91 g/kg,TN含量为0.19~7.5 g/kg;(2)沉积物粒径与TC、OC和TN极显著相关(p<0.01);(3)热融湖塘深度与TC、OC和TN呈极显著正相关(p<0.01),表明热融湖塘越深,C、N含量越高;(4)高寒沼泽草甸区热融湖塘沉积物OC(15.37 g/kg)和氨氮(10.05 mg/kg)含量高,pH(7.99)相对较低,具有产甲烷优势。研究表明,热融湖塘沉积物性质与其所在流域的植被类型有关,植被类型是评估热融湖塘温室气体释放的重要因素。

Thermokarst lakes are common landforms in permafrost regions.The permafrost degradation will accelerate the formation and expansion of thermokarst lakes,which can increase the release of carbon from permafrost regions.There is a close association between the sediment of thermokarst lakes and greenhouse gas release.Therefore,understanding of the physicochemical properties such as carbon and nitrogen content in the sediment is helpful to reveal the response of the carbon and nitrogen cycle in the Qinghai-Tibet Plateau.In this study,116 sediment samples were collected from thermokarst lakes located in the central and eastern Qinghai-Tibet Plateau.The physicochemical properties including total carbon(TC),organic carbon(OC),total nitrogen(TN),and sediment particle size were determined.The relationships among soil TC,OC,TN,sediment particle size and sediment physical and chemical factors were analyzed.The results showed that the contents of TC,OC and TN were the highest in alpine wet meadow,followed by alpine meadow and alpine steppe,the alpine desert had the lowest values.The content of silt and clay in the sediment showed a pattern of alpine wet meadow>alpine steppe>alpine meadow>alpine desert.Results indicated that the sediment TC content is 0.78~110.71 g/kg,OC content is 0.87~85.91 g/kg,TN content is 0.19~7.5 g/kg.Sediment particle size is significantly correlated with TC,OC and TN(p<0.01).The depth of thermokarst lake was significantly positively correlated with TC,OC and TN(p<0.01),indicating that the deeper the thermokarst lakes is,the higher the content of C and N is.The sediments of thermokarst lakes in alpine wet meadow areas are characterized by high OC(15.37 g/kg),high ammonia nitrogen(10.05 mg/kg),and relatively low pH values(7.99),which can benefit the methanogenesis.The results indicated that the sedimental properties of the thermokarst lakes are related to the vegetation type within the catchments,and vegetation type is an important factor affecting the greenhouse gas release from thermokarst lakes.