The Capability of Urban Green Spaces in providing Carbon Sequestration Ecosystem Services

Carbon sequestration in the soil, as the main carbon reserve, can play an important role in reducing atmospheric carbon. In this study, we focused on evaluating the soil carbon storage and sequestration potential in urban green infrastructures including agricultural lands, gardens, parks, and vacant lands because of their considerable extent in Hamadan city. The SAVI index was used to determine the physical units of carbon sequestration ecosystem service using Sentinel-2 satellite images. Then, 108 sampling stations were selected using a systematic-random technique and at each station soil, litter, herbaceous samples, and all allometric data of trees and shrubs were collected in 10-meter plots. Samples were dried and transferred to the laboratory to analyze carbon. Statistical tests were performed using SPSS statistical software. According to the results, agricultural lands are the highest percentage of green infrastructures, and the highest amount of Carbon is stored in soils (312047 tons), tree and shrub covers (90266 tons), grass cover (8383 tons), and litter (771 tons), respectively. Since most of the urban green infrastructure area has been allocated to agricultural lands, gardens, parks, and vacant land, respectively, but the greatest potential of Carbon sequestration and storage has been done by park, garden, agriculture land and vacant land uses. In general, the results of this study showed that the highest carbon sequestration is the highest CO2 capture done by soils in the parks of the city which can be considered as a management option to reduce atmospheric carbon via creating more green spaces in the city of Hamadan.

Cities, like any other complex ecosystem, provide specific ecosystem services to their residents and communities through green infrastructure located in and around urban areas. Green infrastructure in urban space is an interconnected network of green spaces that protect the value and function of the natural ecosystems and provide benefits related to human well-being. One of the most important of these services is carbon sequestration, which can lead to a huge reduction in the amount of CO2 emitted into the atmosphere. The supply of Carbon sequestration potential Ecosystem service is estimated based on the amount of carbon sequestration by soil and vegetation. This study, while extracting green land uses applying Sentinel 2 satellite imagery and field measurements, investigates the amount of storage and potential of organic carbon sequestration in soil and urban vegetation, in order to answer the question of whether soil and vegetation in different land uses (agricultural lands, Gardens, parks and vacant lands) have a significant effect on carbon sequestration. This issue is important in the city of Hamadan due to the considerable extent of green space in the city.

The city of Hamedan is located in western Iran and has an area of about 74 square kilometers. The SAVI index from Sentinel 2 satellite imagery was used to determine the physical units of carbon sequestration ecosystem service. Initially, 108 sampling stations were systematically randomly selected and at each station soil samples, herbaceous cover, litter and tree and shrub species were collected in 10 m2 plots and allometric data of all tree and shrub species were recorded. Then the samples were transferred to the laboratory and analyzed. The statistical analysis was performed using SPSS software. For mapping, green infrastructure polygons were considered as the basis. Total aboveground, underground, and soil biomass were calculated based on sampling plots (10 by 10 meters) and expressed in tons per hectare. The total sequestration map was made by overlaying and summarizing the soil and vegetation sequestration maps. Finally, the average supply values were extracted based on Zonal Statistics, and spatial units of urban ecosystem subdivisions or zonings.

According to the results, the highest area of green infrastructure is related to agricultural use, gardens, parks, and vacant lands, respectively. The highest potential for carbon storage and sequestration in the city of Hamadan is by soil (312047 tons), tree and shrub cover (90266 tons), herbaceous cover (8383 tons) and litter (771 tons), respectively. According to the results, the largest area of urban green infrastructure is related to agricultural fields, gardens, parks and vacant lands, respectively, but the greatest potential for sequestration and storage has been done by parks, gardens, agriculture and vacant land uses. On the other hand, the correlation results showed that there is a positive and significant relationship between soil organic carbon and soil bulk density, so that with increasing organic matter in soil, soil bulk density decreases. This leads to the production of lumps and increases the pores in the soil and then reduces runoff and erosion leading to a reduction in the loss of organic carbon. Total carbon storage varies from 6.996-985.85 tons per hectare (sequestration potential also varies from 0.3540-37.9 tons per hectare). The results of the zonal statistics of the average carbon sequestration potential also vary from 159,277-27 tons per year (with a total carbon storage of 4.7609-11-58 tons per year per neighborhood). The highest average sediment potential is related to neighborhood 217 and the lowest is for neighborhood 109. According to the total statistics, the highest total sediment potential is related to neighborhood 114 and the lowest is related to neighborhood 109. In total, the city of Hamedan has the capacity to store about 54,000 tons of carbon per year and the potential to precipitate about 198,000 carbon dioxide.

In general, the results of this study showed that agricultural lands and gardens have a higher storage potential and carbon sequestration due to their larger area than other uses. However, the highest average carbon sequestration by soil occurs in parks compared to other uses. Parks with an area of about 282.36 hectares, make up approximately 9.81% of the green infrastructure and 3.8% of the total area of the city, which has a very low share compared to other land uses in the city; On the other hand, the highest carbon sequestration by soil occurs in parks compared to other uses, so the creation of green spaces and, especially, the development of parks as a vital option to reduce carbon in the atmosphere can be considered.