Among many greenhouse gases, carbon dioxide(CO2) has increased dramatically during the 20th century. The concentration of CO2 in the atmosphere in the last century has risen significantly ever, from 280 ppm in 1750 to 367 ppm in 1999, which has never exceeded what for the past 420,000 years. emissions affecting climate changes could be made by engineering methods, such as developing alternative energy sources and increasing the efficiency of energy use. However, considering the stability and time and cost-saving aspects, it seems the most efficient method to use the ecosystem. The riparian zone is regarded as a potential space for a reduction of carbon in South Korea, where the government continuously purchases and restores the land in the zone to green space.
However, the restoration project of the riparian zone is in its early stage with the insufficient carbon-reducing researches and the lack of the development and management standards to satisfy the functions of soil carbon stock. If the development and management of the riparian zone goes on the right track, it can help to improve urban ecosystem services by promoting soil productivity, and contribute to the carbon dioxide decrease in the atmosphere, which would have a great effect on gaining the carbon emission rights in the future.
Therefore, the dissertation was aimed: (ⅰ) to identify the characteristic of soil organic carbon(SOC) distribution in the planting areas of the riparian zone, (ⅱ) to quantify the relationship between SOC stock and environmental factors, and finally (ⅲ) to develop a quantitative model and identify the influencing factors for predicting SOC stock in the planting ground of the riparian zone.
The author acknowledged the global carbon cycle and the storage mechanism by a literatures review, both domestic and foreign related to the riparian zone and SOC, and confirmed the possibility for carbon stock in the domestic riparian zone. The investigation into the characteristics of the use and cladding of lands, topography, vegetation and soil environment in the planting areas of the riparian zone was conducted by deducing influential variables linked to the stock of soil organic carbon from preceding studies, also the relation to SOC stock was ascertained. Finally, a model for the predict of SOC stock in the planting areas of the riparian zone was developed through multiple linear regression(MLR) analysis for items with significant correlation, and influential variables were derived.
The result of the analysis, the total SOC stock from 0 to 30 ㎝ was 27.75±3.95 Mg/ha, with total SOC stock by layer was 11.84±1.70 Mg/ha between 0 and 10 ㎝, 8.25±1.37 Mg/ha between 10 and 20 ㎝, 7.66±1.30 Mg/ha at 20∼30 ㎝. The amount of SOC stock in each year of the development was proved to be 38.46±3.14 Mg/ha in 2006, 16.78±6.06 Mg/ha in 2011 and 23.26±9.12 Mg/ha in 2016. The amount of SOC stock before being restored was estimated 35.17±5.31 Mg/ha in agricultural lands, followed by 23.66±12.10 Mg/ha in residential areas, 21.87±9.05 Mg/ha in commercial areas, 19.23±12.48 Mg/ha in industrial areas, and 17.07±11.33 Mg/ha in the barren areas. It turned out that the amount of SOC stock gradually fell down as the depth of the soil came down, and that there was the many amount of SOC in the planting area in 2006 which was the oldest.
It showed that there was a correlation between SOC stock and environmental variables in 27 out of 38 items. MLR analysis was performed, considering the environmental variables identified in the correlation analysis phase. Based on the result, nine models in total were developed: three models at point 0∼10 cm, two at the point of 10∼20 cm, two at the point of 20∼30 cm, and two models at the point 0∼30 cm. The coefficient of determination(R2) and the root mean square error (RMSE) were compared with the data from four additional points to verify and select the developed model. Out of the nine soil organic carbon stock prediction models which had developed, a total of four models were set; one with the smallest actual value and error from each soil layer.
The model selected at 0∼10 cm point showed Adjusted R-square(Adj. R2) as 0.959, F-values as 141.98 and p-value as p<0.000. The influencing variables were seen as organic matter(X1), C/N ratio(X2) and diameter of a breast height(X6).
Y = -3.360 + 4.445X1 + 0.165X2 + 0.415X6
The model selected at 10∼20 cm point showed Adj. R2=0.933, F=25.94 and p<0.000, and the influencing variables were seen as organic matter(X1) and sand content(X3).
Y = 10.909 + 3.724X1 - 0.119X3
The model selected at 20∼30 cm point showed Adj. R2=0.861, F=40.15 and p<0.000, and the influencing variables were seen as organic matter(X1), sand content(X3) and C/N ratio(X2).
Y = 18.784 + 2.933X1 ? 0.260X3 + 0.257X2
The models selected at points 0∼30 cm were significantly shown with Adj. R2=0.977, F=151.23 and p<0.000, and the influencing variables were analyzed as organic matter(X1), amount of fallen leaves(X5), C/N ratio(X2), sand content(X3) and aggregate percentage(X4).
Y = 19.089 + 3.145X1 + 0.400X5 + 0.141X2 ? 0.124X3 + 0.065X4
Therefore, the total number of variables giving an impact on SOC stock in the planting areas of the riparian zone was expected to be six; organic matter, the C/N ratio, sand content, the aggregate percentage, the amount of fallen leaves and the diameter at the height as one''s breast. It is believed that the planting area of the riparian zone needs to be focused on these six items to improve the carbon stock in the future, when developing and managing of the plant-base.
This study had a limit of the lack of the small number of samples, the biomass cover degree, and the exclusion of the vegetation environment variables such as a crown volume. Nevertheless, the results of this study quantified the distribution characteristics and stock of soil organic carbon in the plating areas of the riparian zone, which are relatively understudied compared to the domestic forest and agricultural areas, and the streets and parks in urban areas. In addition, it is meaningful that a quantitative model for predicting SOC stock in the future riparian zone has developed, and the influencing variables for improving the SOC stock has been presented. This will be helpful to quantify the more detailed amounts of soil organic carbon storage that shows differences between the natural, human and regional characteristics in terms of the country. It is also believed to contribute to the mitigation of climate changes and the carbon emissions among countries. Besides, it could be used as a standard data and an evaluation indicator to form and manage the planting ground in order to make progress in the carbon-reducing in the riparian zones of the four major rivers in the country.