The potential of pulau dua nature reserve as a blue carbon reservoir in climate change mitigation using Sentinel-2 MSI imagery

Climate change is a long-term change in weather patterns that occurs on a global scale. Climate change has had impacts in various parts of the world. Mangrove ecosystems in Pulau Dua Nature Reserve contribute to the improvement of climate change through blue carbon reserves. The study aims to determine the blue carbon reservoir in the Pulau Dua Nature Reserve area using Sentinel-2 MSI imagery. The research was conducted from March to May 2023 using remote sensing methods. Data collection using open-source image Sentinel-2 image, then processing and analyzing data with composite images and finally calculating carbon stocks. The results showed that the blue carbon reservoir obtained was 537.89 tons, which means that the mangrove ecosystem in the Pulau Dua Nature Reserve is able to store more carbon than other forest types. This is because the mangrove ecosystem has great potential in reducing and dealing with disasters due to climate change in the era of global warming.


Introduction
Pulau Dua Nature Reserve (CAPD) is one of the conservation areas located at the West Java Natural Resources Conservation Center (BBKSDA).The area is characterized by a unique mangrove ecosystem and the presence of migratory and local waterbirds.As a conservation area, the importance of the preservation function is far greater than the utilization of resources.The consequence of a nature reserve that functions as an area for preserving plant and animal diversity, a life support systems area, a place for research, scientific development, education, and supporting cultivation is that there is a high emphasis on conservation aspects.Therefore, the natural resources and ecosystems of the CAPD area need to be managed, maintained, preserved and optimally utilized in order to become a source and support for human life, both for present and future generations [1].
Pulau Dua, known as Bird Island, was designated as a Nature Reserve based on BG (Besluit Gouvernements) dated 30 July 1937 Number 21 Stbl 49 with an area of 8 ha.Pulau Dua is a small island with a lowland topography, in the northern part dominated by mangrove forests.At first, part of the island was an agricultural area, but now it has been overgrown with bushes so that the agricultural area 1315 (2024) 012039 IOP Publishing doi:10.1088/1755-1315/1315/1/012039 2 is getting narrower.Pulau Dua is a small coral island located about 600 m from the eastern area and is includes in the nature reservation area.
The impact of global climate change affects many aspects of life.Indonesia as a maritime country is not immune from these consequences, especially in the marine sector.The increase in earth temperature causes melting of ice and glaciers at the north and south poles and this event affects the expansion of sea water mass and sea level rise.This phenomenon will threaten the lives of coastal communities and affect ecosystems and marine biota and will directly disrupt the maritime sector [2].Changes in ocean conditions due to climate change affect marine ecosystems and human activities that utilize the sea.The increase in sea temperature will further risk coral bleaching and a decrease in capture fisheries production.
Coastal ecosystems containing mangroves, tidal marshes and seagrass beds provide impacts and benefits to climate change mitigation and adaptation along the coast globally.Coastal areas provide protection from coastal abrasion, protection from storms and sea level rise, prevention of tidal flooding, regulating coastal water and air quality, providing coastal biodiversity habitat and providing food sources for coastal communities.Based on the role and usefulness of Blue Carbon, further information and data are needed to obtain information on the potential of the Dua Island Nature Reserve as a Blue Carbon Reservoir in Climate Change Mitigation, namely with accurate and effective methods such as object-based classification methods and pixel-based classification in images [3].Land classification techniques with images using remote sensing are divided into three parts, namely pixel-based classification techniques, sub-pixel-based classification and object-based classification [4].Pixel-based classification is a classification used for remote sensing with training areas in the image then categorized according to pixels and divided into several land covers [3].While object-based classification by classifying segment parts in the form of a collection of pixels that have similarities with each other based on spectral characteristics.Remote sensing will obtain image data, an image is a combination of points, lines, fields, and colors in the form of an imitation of an object obtained.The image obtained from remote sensing is called remote sensing, which is monitoring the earth's surface from a distance to space using reflected electromagnetic waves [5].
With the remote sensing, human activities in the form of observing an area can be done easily and quickly with a certain area without having to go to the location directly.After the image data is obtained through remote sensing, data processing will be carried out using a computer in digital format.Digital spatial data processing obtained from remote sensing is called GIS or Geographic Information System.Image data processing in digital format usually uses software on a computer that will analyze data such as Er mapper or ArcGis [6].The implementation of remote sensing in the potential of Pulau Dua Nature Reserve as a Blue Carbon Reservoir in Climate Change Mitigation can be done with Sentinel-2 images through index calculation.Sentinel-2 image is an infrared image that has good spatial and temporal resolution with open access and free of charge.Indices commonly used to estimate fire severity are the Normalized Difference Vegetation Index (NDVI) and the Normalized Burn Ratio (NBR).The two indices were compared in order to get the best index to estimate the potential level of Pulau Dua Nature Reserve as a blue carbon reservoir in climate change mitigation.Therefore, the study aims to determine information on the potential of the Pulau Dua Nature Reserve as a blue carbon reservoir in climate change mitigation using Sentinel-2 MSI imagery.

Study Site and Period
The report was prepared at the IPB University Campus, Bogor, West Java, Indonesia.The study was conducted from March to May 2023, and activities included secondary data collection (library searches and electronic publications) and data processing.Pulau Dua Nature Reserve in Indonesia is one of the mangrove forests located in Banten Bay, Sawah Luhur Village, Kasemen District, Serang Regency.Geographically, it is located at 106º11'38" -106º13'14" East longitude and 6º11'5" -6º12'5" South latitude (Figure 1).

Tools and materials
The material used in this research is Sentinel-2 image data in TIF file format.The TIF file used contains image data from Pulau Dua Nature Reserve, Sawah Luhur Village, Kasemen Sub-District, Serang City, Banten Province, Indonesia.The tools used in this research include a set of computers with several pieces of software such as Microsoft Word 2013, Microsoft Excel 2013 for graphic processing, Google Earth Engine and RStudio ver.2022.02.1+461 for image capture, and ArcGIS desktop 10.3 for data processing in Geographic Information System (GIS) format.

Data Collection
This research uses the open-source image of Sentinel-2 MSI (MultiSpectral Instrument).Sentinel-2 images are satellite images with wide swaths and medium spatial resolution, revisit the same location every 5 days, and can be used for land cover monitoring studies, including vegetation, soil and water, as well as water networks and coastal areas.Sentinel-2 MSI has the main objective to conduct land monitoring with global coverage of the Earth's surface every 10 days with 1 satellite and 5 days with 2 satellites consisting of sentinel-2A and Sentinel-2B satellites.

Data processing and analysis
Composite band is the initial stage in processing Sentinel-2 image data.The composite band stage is carried out with the ArcMap 10.3 spatial application.After the composite band stage, the map with TIF format is classified in classifying the NDVI class.Before being classified, the composite band uses the following equation 1 in analyzing the NDVI value.The image from the NDVI analysis was delineated with the boundaries of the sub-district administrative area.NDVI values were then classified into 3 classes to facilitate interpretation and analysis (Table 1).

Table 1. range of density levels.
After the NDVI analysis stage, the composite image data was classified to see the classification of land cover classes in the Pulau Dua Nature Reserve area.Layouting is the last stage in data processing.Map formation by adding map elements such as coordinate lines, legends, map titles, map sources, and so on.In addition, inserting shapefile data in the form of insert maps to see the Pulau Dua Nature Reserve area using data frames.

Calculation of Carbon Reserves
According to the [20] about 47% of carbon is contained in organic matter.Therefore, to estimate the amount of carbon stored, we can multiply the biomass by a multiplying factor of 47% or 0.47.The equation 2 is as follows: Cn (tonnes/ha) = Biomass (tonnes/ha) x 0.47 Description: Cn = carbon stock per hectare in each plot (tonnes/ha)

Results and Discussion
Forests are the most dominant area in compiling the role of ecosystem services in the environment [7].This is because forests have naturally provided benefits and supported life, both directly and indirectly.One of the environmental services from forests is carbon sequestration services.Forests play an important role in climate change, namely as carbon sinks and carbon storage.
Biomass refers to the total amount of living matter present above the tree surface, and is usually measured in dry weight tons per unit area [8].To calculate the biomass of a forest, variables such as tree diameter and height are commonly used.However, in this study, only density data was taken using NDVI.The biomass value obtained can give an idea of how much carbon is present or stored in the stand.This is because about 50% of plant biomass consists of carbon [9].Remote sensing of mangrove vegetation is based on two important properties, namely that mangroves have green leaves (chlorophyll) and mangroves grow in coastal areas.Mangrove forests can be detected through the use of remote sensing technology, where transitional areas between land and sea show distinctive patterns in the recordings, in contrast to other terrestrial vegetation [10].Remote sensing is a field of knowledge and skills that allows the retrieval of information about an object or area on the earth's surface without having to make direct contact with the object or area being studied.Remote sensing technology can be used as one of the methods for estimating carbon stocks because it is superior in terms of coverage of large areas, and lower costs when compared to field surveys.The concept of remote sensing which explains that each different object on the earth's surface provides different spectral reflections makes remote sensing desirable for use in a study related to objects on the earth's surface, one of which is the study of vegetation related to carbon stocks.The availability of time series image data covers the entire territory of Indonesia, is free to download, and the resolution (spatial, temporal, and radiometric) is fairly good [11].Remote sensing techniques and geographic information systems (GIS) utilizing the results of satellite image analysis are the most effective methods for mapping mangrove forests.
No. NDVI ranges Density levels 1 -1 to 0.32 Sparce 2 0.32 to 0.42 Medium 3 0.24 to 1 Dense Estimation of biomass using remote sensing is carried out through analysis of data obtained from a certain time and place without direct contact with the object or area under study.Data that is commonly used in remote sensing is in the form of digital imagery recorded through non-camera sensors in the form of satellites such as: Landsat ETM+, SPOT, NOAA, Quickbird, and Iconos.Therefore, estimating carbon stocks with remote sensing in a small area of land will be better using satellite imagery data with high spatial resolution such as: Quickbird or Iconos (Figure 2).However, there are obstacles encountered, namely the limited access to image data with high spatial resolution (paid), so an alternative image data is needed that is easily accessible with high spatial resolution.One alternative image data that is easy to access with a fairly high spatial resolution is Google Earth image data.However, there are drawbacks to Google Earth image data, including [12]: there is no metadata information regarding the acquisition of the image data used and how much accuracy the images are given, and the images are stored in JPEG format so they are not yet georeferenced.In addition, the image data displayed on Google Earth comes from other satellites such as: Quickbird, Iconos, or Geoeye-1, making the availability of image data on Google Earth limited at certain times.there is no metadata information regarding the acquisition of image data used and how much accuracy the image is given, and the image is stored in JPEG format so it is not yet georeferenced.In addition, the image data displayed on Google Earth comes from other satellites such as: Quickbird, Iconos, or Geoeye-1, making the availability of image data on Google Earth limited at certain times.there is no metadata information regarding the acquisition of image data used and how much accuracy the image is given, and the image is stored in JPEG format so it is not yet georeferenced.In addition, the image data displayed on Google Earth comes from other satellites such as: Quickbird, Iconos, or Geoeye-1, making the availability of image data on Google Earth limited at certain times.The estimated value of carbon stocks using NDVI value is estimated at 537.89 tons.Mangrove ecosystems play an important role in maintaining balance in coastal areas and small islands due to their high productivity and contribution as a source of organic carbon and other nutrients [13].Mangroves provide a wide range of ecosystem services, including nutrient cycling, sediment capture and habitat for a variety of organisms.One of the most important functions is as a carbon (C) buffer in these ecosystems.The carbon stores present in mangrove ecosystems are enormous, making them important in maintaining the balance of the surrounding environment.The carbon reserves stored in mangrove forests far exceed those of other forests.The carbon mainly comes from decaying biomass, decomposed, and then stored in the soil or sediment layer which is considered as the total carbon stock [14].The condition of the mangrove forest ecosystem can be reviewed using satellite imagery by analyzing the condition of the mangrove ecosystem using several vegetation indices, one of which is the NDVI method.NDVI which has a strong correlation with mangrove vegetation density is one of the most widely used vegetation indices [15].Remote sensing of mangrove vegetation is based on two important properties, namely that mangroves have green leaves (chlorophyll) and mangroves grow in coastal areas.Mangrove forests can be detected through the use of remote sensing technology, where transitional areas between land and sea show distinctive patterns in the recordings, in contrast to other terrestrial vegetation [10].
According to the United States Environmental Protection Agency there are at least four impacts of climate change that occur in coastal areas, namely sea level rise, storm surges and rainfall, impacts on coastal water temperatures, and finally impacts on sea water acidification.In connection with the issue of climate change and global warming, the way to maintain the function of environmental services to absorb and store carbon is to maintain and maintain forest vegetation from deforestation and degradation activities.Biomass value is influenced by tree density and tree diameter.The higher the tree density value, the greater the biomass value at that location (Figure 3).Biomass value is influenced not only by tree density but also by the diameter of the tree itself.The larger the diameter of the tree, the higher the biomass value.The effect of stem diameter on tree biomass value is much more significant than density, in line with [16] view that tree dimensions (diameter and height) have a close relationship with biomass, especially with tree diameter.When a tree grows, it will produce greater biomass and stored carbon values because the photosynthesis process absorbs CO2 from the atmosphere and converts it into biomass that is distributed to leaves, twigs, trunks and roots.This results in an increase in tree diameter and height [17].
The estimated value of carbon stocks in the vegetation density data above can occur because it is influenced by the type and condition of the ecosystem in accordance with the statement of [18], that the potential for carbon sequestration by ecosystems depends on the type and condition of the ecosystem, namely species composition, structure, and age distribution (specifically for forests).If a land use system involves trees with species that have a high wood density, the biomass on the land will be higher than land that relies on species with low wood density.On the other hand, the amount of carbon stock is basically influenced not only by the structure and composition of the vegetation that makes up the forest/woodland but also by the value of the stem diameter of the vegetation itself.[19] explains that the total carbon content is strongly influenced by tree diameter and density, but the density factor does not provide total carbon if the tree diameter is small.

Conclusion
Pulau Dua Nature Reserve (CAPD) is an area that has a mangrove ecosystem.This ecosystem has a large potential blue carbon value.Based on data collection using Google Earth Engine based on cloud computing integrated with Arcmap, the blue carbon value obtained is around 537.89 tons.Data analysis using Rstudio shows that the density of a mangrove is directly proportional to the greater value of carbon.This is certainly very good, especially can be a reference by the government in providing regional management policies in dealing with climate change.

Figure 1 .
Figure 1.NDVI map of the Pulau Dua Reserve area.

Figure 2 .
Figure 2. Distribution of mangrove biomass in Pulau Dua Nature Reserve.

Figure 3 .
Figure 3. Visualization of mangrove biomass density in Pulau Dua Nature Reserve.