Importance of mangrove plantations for climate change mitigation in Bangladesh

Mangroves have been identified as blue carbon ecosystems that are natural carbon sinks. In Bangladesh, the establishment of mangrove plantations for coastal protection has occurred since the 1960s, but the plantations may also be a sustainable pathway to enhance carbon sequestration, which can help Bangladesh meet its greenhouse gas (GHG) emission reduction targets, contributing to climate change mitigation. As a part of its Nationally Determined Contribution (NDC) under the Paris Agreement 2016, Bangladesh is committed to limiting the GHG emissions through the expansion of mangrove plantations, but the level of carbon removal that could be achieved through the establishment of plantations has not yet been estimated. The mean ecosystem carbon stock of 5-42 years aged (average age: 25.5 years) mangrove plantations was 190.1 (±30.3) Mg C ha^-1 , with ecosystem carbon stocks varying regionally. The biomass carbon stock was 60.3 (±5.6) Mg C ha^-1 and the soil carbon stock was 129.8 (±24.8) Mg C ha^-1 in the top 1 m of which 43.9 Mg C ha^-1 was added to the soil after plantation establishment. Plantations at age 5 to 42 years achieved 52% of the mean ecosystem carbon stock calculated for the reference site (Sundarbans natural mangroves). Since 1966, the 28,000 ha of established plantations to the east of the Sundarbans have accumulated approximately 76,607 Mg C year^-1 sequestration in biomass and 37,542 Mg C year^-1 sequestration in soils, totaling 114,149 Mg C year^-1 . Continuation of the current plantation success rate would sequester an additional 664,850 Mg C by 2030, which is 4.4% of Bangladesh's 2030 GHG reduction target from all sectors described in its NDC, however, plantations for climate change mitigation would be most effective 20 years after establishment. Higher levels of investment in mangrove plantations and higher plantation establishment success could contribute up to 2,098,093 Mg C to blue carbon sequestration and climate change mitigation in Bangladesh by 2030.

Impact of an extreme monsoon on CO2 and CH4 fluxes from mangrove soils of the Ayeyarwady Delta, Myanmar

Mangrove ecosystems can be both significant sources and sinks of greenhouse gases (GHGs). Understanding variability in flux and the key factors controlling emissions in these ecosystems are therefore important in the context of accounting for GHG emissions. The current study is the first to quantify GHG emissions using static chamber measurements from soils in disused aquaculture ponds, planted mangroves, and mature mangroves from the Ayeyarwady Delta, Myanmar. Soil properties, biomass and estimated net primary productivity were also assessed. Field assessments were conducted at the same sites during the middle of the dry season in February and end of the wet season in October 2019. Rates of soil CO₂ efflux were among the highest yet recorded from mangrove ecosystems, with CO₂ efflux from the 8 year old site reaching 86.8 ± 17 Mg CO₂ ha^-1 yr^-1 during February, an average of 862% more than all other sites assessed during this period. In October, all sites had significant rates of soil CO₂ efflux, with rates ranging from 31.9 ± 4.4 Mg CO₂ ha^-1 yr^-1 in a disused pond to 118.9 ± 24.3 Mg CO₂ ha^-1 yr^-1 in the 8 year old site. High soil CO₂ efflux from the 8 year old site in February is most likely attributable to high rates of primary production and belowground carbon allocation. Elevated CO₂ efflux from all sites during October was likely associated with the extreme 2019 South Asian monsoon season which lowered soil pore salinity and deposited new alluvium, stimulating both autotrophic and heterotrophic activity. Methane efflux increased significantly (50-400%) during the wet season from all sites with mangrove cover, although was a small overall component of soil GHG effluxes during both measurement periods. Our results highlight the critical importance of assessing GHG flux in-situ in order to quantify variability in carbon dynamics over time.

Mapping Large-Scale Mangroves along the Maritime Silk Road from 1990 to 2015 Using a Novel Deep Learning Model and Landsat Data

Mangroves are important ecosystems and their distribution and dynamics can provide an understanding of the processes of ecological change. Meanwhile, mangroves protection is also an important element of the Maritime Silk Road (MSR) Cooperation Project. Large amounts of accessible satellite remote sensing data can provide timely and accurate information on the dynamics of mangroves, offering significant advantages in space, time, and characterization. In view of the capability of deep learning in processing massive data in recent years, we developed a new deep learning model—Capsules-Unet, which introduces the capsule concept into U-net to extract mangroves with high accuracy by learning the spatial relationship between objects in images. This model can significantly reduce the number of network parameters to improve the efficiency of data processing. This study uses Landsat data combined with Capsules-Unet to map the dynamics of mangrove changes over the 25 years (1990–2015) along the MSR. The results show that there was a loss in the mangrove area of 1,356,686 ha (about 21.5%) between 1990 and 2015, with anthropic activities such as agriculture, aquaculture, tourism, urban development, and over-development appearing to be the likely drivers of this decline. This information contributes to the understanding of ecological conditions, variability characteristics, and influencing factors along the MSR.

The impacts of degradation, deforestation and restoration on mangrove ecosystem carbon stocks across Cambodia

Mangrove forest conservation can help reduce global C emissions. Despite this benefit to climate change mitigation and adaptation, mangrove forests are being deforested or degraded at an alarming rate, though restoration efforts may offset these losses. The impacts of deforestation to C stocks are relatively intuitive and result in significant decreases in C stocks. It remains unclear how degradation from selective harvesting of trees affects C stocks or how effective restoration efforts are at restoring C stocks. Furthermore, total ecosystem C (TEC) stocks of pristine mangroves can significantly vary spatially. To address these issues, we conducted an intensive, national assessment of mangrove forests across Cambodia using a grid approach to: 1) examine how land use land cover (i.e., pristine, deforested, degraded, and restored forests) impacts TEC stocks, and 2) how TEC stocks vary spatially across the country. TEC stocks from deforested mangroves were always lower than pristine forests, resulting in an overall loss of 60% C (480 Mg C ha^-1). However, TEC stocks from degraded and 25-year-old restored mangroves forests did not differ from pristine forests. Mean TEC in mangroves was 784.7 ± 30.1 Mg C ha^-1, decreasing from 957.2 ± 32.8 Mg C ha^-1 in the northern region to 628.9 ± 33.1 Mg C ha^-1 in the central region to 386.2 ± 19.1 Mg C ha^-1 in the southern region of Cambodia. Intensive sampling in mangroves across Cambodia verified impacts of deforestation reported elsewhere, revealed the lack of degradation impacts on TEC stocks, and demonstrated the effectiveness of restoration on TEC stocks after only 25 years. Our gridded sampling approach was able to capture spatial variability across Cambodia and provide a more realistic TEC stock information that can be used for national reporting or participation in C markets.