| Summary: | 碩士 === 弘光科技大學 === 職業安全與防災研究所 === 101 === The human activity patterns began to alter since the industrial revolution that increasing global greenhouse gas emissions resulted in changes of ecosystems, agriculture and regions such as Arctic or Africa. Therefore, the United Nation Framework Convention on Climate Change (UNFCCC) was enacted to decrease greenhouse gas emissions. In 1997, Kyoto Protocol was signed to require the reduction targets and timetables while afforestation was recognized as a feasible approach for reducing greenhouse gas emissions. The study objective was to estimate carbon sequestration amounts by afforestation from heavy metal contaminated farmland control sites of Changhua county in central Taiwan. The carbon sequestration amounts were estimated by tree biomass growth model and carbon content percentage that the different tree species were compared. Moreover, the soil carbon storage amounts were estimated by on-site sampling and analysis soil organic carbon amounts which provided the baseline for comparison with that of future afforestation.
First of all, 15 common broad-leaved forest tree species were seleted to estimate and compare the carbon sequestration amounts that the highr were Acacia confusa, Zelkova serrata and Fraxinus formosana of 1.33, 1.28 and 1.26 kg CO2/m3, respectively. Moreover, three heavy metals contaminated farmland sites such as Xiandong, Zhuanyao and Citong in Changhua were chosen to conduct on-site soil samling and analysis of organic carbon for estimation of soil carbon storage amounts. Initially, the tree species were screened by area suitability to obtain Acacia confuse and Fraxinus formosana. The tree biomass carbon sequestration were estimated by biomass(WE) multipling with carbon content percentage(C%) that WE was obtained by two equations: curves of current annual increment of aboveground biomass(CAIAB) and tree volume. The dry specific weight S0 and C% were checked from Table 3.2.
The CAIAB equations of Acacia confuse were quoted from Lin(2007) in Miaoli and Lin(2009) in Taitung: (a)y=2.793–1.061x+0.088x2–0.001x3, (b)y=1.1749–0.5925x+0.1016x2–0.0025x3. The tree volume equations were 1/logV=0.33569364+2.20049718(1/A) from Liu and Lin (1968). Moreover, the CAIAB equations of Fraxinus formosana were by Lin(2010): y=–0.0371x2+1.3936x–2.8174. The tree volume equations by Lin(2002) were V=0.0042-0.0038A+0.0009A2-0.00002A3. From the Forestry Bureau database, suppose 1500 trees/ha and the average volume growth of 5-10 m3/ha•yr, the CO2 sequestration by afforestation is 7.45-14.9 ton/ha•yr, average 11.175 ton/ha•yr. Besides, the soil carbon storge was estimated by equation A(m2)×H(m)×D(ton/m3)×C(%) that Desity D of 0.2 ton/m3 (for farmland) was from chen and Hseu(1997). Area A(m2) was selected from control sites of TWEPA(Taiwan Envirommental Protection Agency) while Height H(m) and C% were from on-site sampling and analysis. From the results, the carbon sequestration (ton/ha) of 20-year Acacia confusa estimated by tree volume equation, CAIAB and Forestry Bureau were 385.37, 34.15(Miaoli), 108.75(Taitung) and 223.50, respectively that Fraxinus formosana were 350.32, 172.18 and 223.50, respectively. Therefore, The carbon of tree biomass for Xiandong, Zhuanyao and Citong sections by Acacia confusa were 150.95 (0.3917 ha), 70.14 (0.1820 ha) and 70.14 (0.1820 ha), respectively that Fraxinus formosana were 137.22, 63.76 and 63.76, respectively. Furthermore, soil carbon storage amounts of Xiandong (0.3917 ha), Zhuanyao (0.1820 ha) and Citong (0.1820 ha) were 2.54, 1.64 and 0.96 (tons), respectively with soil depth 0-30 cm. The soil bulk density usually increases to an average value of 1.3 ton/m3 after afforestration. If the bulk density of 1.3 ton/m3 (for usual land) with soil depth 0-30 cm was assumed, the soil carbon storage amounts of 16.51, 10.66 and 12.16 were calculated.
Therefore, phytoremediation by afforestation is an environmental friendly remediation including carbon-fix, soil remediation, soil and water conservation, green landscape and ecological conservation for national land resources effectiveness. However, there are no any contaminated framlands applied to the proved projects with passed small-scale methodologies and baseline scenarios that needs further research and disscussions. On the other hand, TWEPA has not announced the organizations of afforestation project audit, validation and verification that hinders the implementation of afforestation. Secondly, people maintain or cut trees in heavy metal containmated farmlands after afforestation may expose or contact the contaminants. The heavy may be directly and indirectly enter into food chain by the insects and other animals activities that suggest to conduct health risk assement. Finally, the tolerance and absorption of heavy metals for various tree species affect the removal of soil heavy metals and control site deletion that suggests to plan the pot, pilot and site tests for the future.
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