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地球陆地岩石的风化过程要消耗大气或土壤中的CO2,成为大气CO2巨大的汇。以中国云南小江流域为例,研究了典型岩溶地区碳酸盐岩风化吸收CO2(碳汇)强度与土地利用变化之间的关系。选择了有代表性的12块土地及其利用变化的25个地下水监测点,分析了1982年、2003年这些监测点的600多组地下水化学监测数据。12块土地利用变化中,有4块为林地变耕地,3块未利用地变耕地,4块未利用地变林地,1块为林地变建设用地。研究结果表明:首先,土地利用变化后,地下水化学成分变化极大;第二,将风化过程中吸收大气或土壤中CO2的那部分C(用HCO3-表示)与整个风化过程中参与风化的全部C的百分比,定义为碳酸盐岩化学风化对土壤或大气CO2吸收强度(简写为CIS,%),推出了计算式子为CIS(%)=100×[1-(Ca2++Mg2+)total waters)/HCO3-total waters]。估算了4种土地利用类型从1982年到2003年22年间CIS的变化值。结果是,(1)林地的CIS比未利用地高,前者为48.84%,后者47.66%;(2)未利用地转变为耕地后,CIS平均减少了7.85%;林地转变为耕地后,CIS平均减少了8.59%;林地转变为建设用地后,CIS平均减少了1.66%,而未利用地转变为林地后,CIS平均增加了1.74%。(3)讨论了土地利用变化对CIS的影响机理,如未利用地或林地变为耕地后,(NH4)2PO4、CO(NH2)2、NH4NO3、(NH4)2SO4等氮肥的大量使用,硝化后产生的硝酸等干扰或抵消了碳酸对碳酸盐岩化学风化作用,导致了岩溶地下水中Ca2+,Mg2+离子的相对增多,HCO3-离子相对减少,促使CIS减小。
The weathering of Earth’s terrestrial rocks consumes CO2 in the atmosphere or in the soil and becomes a huge sink of atmospheric CO2. Taking Xiaojiang watershed in Yunnan as an example, the relationship between carbon dioxide (CO 2) uptake intensity and land use change of carbonate rocks in typical karst regions was studied. A total of more than 600 sets of groundwater chemical monitoring data were selected from these 12 monitoring sites in 1982 and 2003 by selecting 12 representative sites and 25 groundwater monitoring sites that make use of the changes. Among the 12 land-use changes, 4 were cultivated land for forest land, 3 cultivated land for unutilized land, 4 unused land for change of forest land, and 1 for woodland conversion. The results show that: firstly, the chemical composition of groundwater changes greatly after the land use change; secondly, the part C (denoted as HCO3-) that absorbs atmospheric CO2 or CO2 in the weathering process and all the weather-related chemicals involved in the weathering process The percentage of C, defined as the CO2 absorption intensity of the chemical weathering of the carbonate rock to the soil or the atmosphere (abbreviated as CIS,%), is calculated as CIS (%) = 100 × [1- (Ca2 + Mg2 +) waters / HCO3-total waters]. The changes of CIS in four types of land use from 1982 to 2003 were estimated. As a result, (1) the CIS of forest land was higher than that of unutilized land, with the former 48.84% and the latter 47.66%; (2) CIS decreased by 7.85% on average after unused land was converted into cultivated land; after the conversion of cultivated land to CIS An average reduction of 8.59%. After the conversion of forestry land to construction land, CIS decreased by 1.66% on average, while CIS increased by 1.74% on average after unused land was converted to forest land. (3) Discussed the mechanism of the impact of land use change on CIS, such as the extensive use of (NH4) 2PO4, CO (NH2) 2, NH4NO3, (NH4) 2SO4 and other nitrogenous fertilizers after unused land or woodlands into farmland, Generated nitric acid or interfere with or counteract the chemical weathering of carbonates on carbonate rocks, resulting in the relative increase of Ca2 + and Mg2 + ions in karst groundwater and the relative reduction of HCO3- ions, leading to the decrease of CIS.