土地覆盖对岩溶地下河碳汇的影响——以广西打狗河流域为例

以广西打狗河为例,对比分析河流东、西两岸地下河的土地覆盖差异及其对岩溶碳汇的影响。打狗河东岸林地占56.13%,耕地占15.15%;而西岸林地、耕地分别只占20.8%、12.95%。但西岸的裸岩和荒地比例大,分别占29.57%和25.95%,而东岸分别占14.19%和10.98%。植被和土壤覆盖差异导致了东、西两岸碳循环的地球化学指标有明显的差异,东岸地下河水的HCO3-、Ca2+、PCO2(平均分别是233.71mg/L、85.5mg/L、909.46Pa)明显高于西岸(分别为177.26mg/L、64.65mg/L、257.37Pa),而东岸的SIC、pH值(分别为0.12和7.40)又低于西岸(分别是0.38和7.85)。因此,东岸有更强的岩溶动力条件,东岸地下河的平均碳汇强度比西岸高14%,其中,东岸下桥地下河的碳汇强度是西岸旦峒地下河的3.7倍。东西岸地下河水的δ13CDIC、TOC资料也进一步证明了土地覆盖条件对地下河岩溶碳汇具有重要的影响。 

Influence of land covers on carbon sink of underground river:A case in the Dagouhe Basin in Guangxi

Taking the Dagouhe Basin in Guangxi Autonomous Region as a study area,the influences of land covers on carbon sink of underground rivers on both the east and west banks are analyzed in this paper.The forest land and farmland respectively occupy 56.3 % and 15.15 % of the total area on the east bank,but in the west bank they only respectively occupy 20.8 % and 12.95 % of the total area.The bare rocky land and wasteland respectively occupy 29.57 % and 25.95 % of the total area on the west bank,while the bare rocky land and wasteland only respectively occupy 14.19 % and 10.98 % of the total area on the east bank.The differences of land covers on the east bank and the west bank of the Dagouhe lead to a lot difference of geochemical indexes in the carbon cycle of the underground river between the two banks,for example,HCO-3,Ca2＋ and PCO2 contents of the underground river on the east bank,being 233.71 mg/L,85.5 mg/L and 909.46 Pa respectively,are higher than that on the west bank,177.26 mg/L,64.65mg/L and 257.37 Pa respectively;but SIc and pH value of the underground river on the east bank,being 0.12 and 7.40 respectively,are lower than that on the west bank,0.38 and 7.85 respectively.Therefore,there are stronger karst dynamic conditions on the east bank.That is why the mean carbon sink intensity of the underground river on the east bank is 14 % higher than that on the west bank.Especially,the carbon sink intensity of the Xiaqiao Underground Stream on the east bank is 3.7 times as that of the Dandong Underground Stream on the west bank of the Dagouhe.The water δ13CDIC and TOC data of the underground river on the two banks can further prove that some carbon content of the underground river water comes from the land cover environments.Land cover has a very important influence on carbon sink intensity of the underground river.