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The research proposes a model to estimate the carbon stock in mangrove forests from multispectral images from Landsat 8 and Sentinel 2B satellites. The Gramame River mangrove, located on the southern coast of Paraíba State, Brazil, was adopted as the study area. Carbon stocks in biomass, below and above ground, were measured from a forest inventory, and vegetation indices were processed on the Google Earth Engine (GEE) platform. To define the fit curves, linear and non-linear regressions were used. The choice of the model considered the highest coefficients of determination (R2), the biomass and carbon stock were estimated from the equations. The biomass carbon stock, calculated from field data, corresponded to 22.27 Gg C, equivalent to 81.75 Gg CO2, with 13.85 Gg C (50.84 Gg CO2) and 8.42 Gg C (30.91 Gg CO2) stored in biomass above and below ground, respectively. Among the models fitted to the indices calculated from Landsat 8 images, NDVI was the one that best explained the spatial distribution of biomass and carbon, with 90.26%. For Sentinel 2B, SAVI was able to explain 80.76%. The total estimated plant carbon stocks corresponded to 26.66 Gg (16.20 Gg C above and 10.36 Gg C below ground) for Landsat 8 and 27.76 Gg C (16.93 Gg C above and 10.83 Gg C below ground) for Sentinel 2B. The proposed work methodology and the suggested mathematical models can be replicated to analyze carbon stocks in other locations, especially in the Americas, because they share the same species. [ABSTRACT FROM AUTHOR]

Mangroves forests may be important sinks of carbon in coastal areas but upon their death, these forests may become net sources of carbon dioxide (CO 2) and methane (CH 4) to the atmosphere. Here we assessed the spatial and temporal variability in soil CO 2 and CH 4 fluxes from dead mangrove forests and paired intact sites in SE-Brazil. Our findings demonstrated that during warmer and drier conditions, CO 2 soil flux was 183 % higher in live mangrove forests when compared to the dead mangrove forests. Soil CH 4 emissions in live forests were > 1.4-fold higher than the global mangrove average. During the wet season, soil GHG emissions dropped significantly at all sites. During warmer conditions, mangroves were net sources of GHG, with a potential warming effect (GWP100) of 32.9 ± 10.2 (±SE) Mg CO 2 e ha−1 y−1. Overall, we found that dead mangroves did not release great amounts of GHG after three years of forest loss. • Soil CO 2 fluxes were higher in pristine mangrove forests. • Warmer and drier periods increased GHG fluxes from mangrove soils. • Low GHG fluxes from dead mangrove forests after three years of forest loss • Mangrove soil GHG fluxes are much lower when compared to land use emissions. [ABSTRACT FROM AUTHOR]

Mangroves have among the highest carbon densities of any tropical forest. These 'blue carbon' ecosystems can store large amounts of carbon for long periods, and their protection reduces greenhouse gas emissions and supports climate change mitigation. Incorporating mangroves into Nationally Determined Contributions to the Paris Agreement and their valuation on carbon markets requires predicting how the management of different land‐uses can prevent future greenhouse gas emissions and increase CO2 sequestration. We integrated comprehensive global datasets for carbon stocks, mangrove distribution, deforestation rates, and land‐use change drivers into a predictive model of mangrove carbon emissions. We project emissions and foregone soil carbon sequestration potential under 'business as usual' rates of mangrove loss. Emissions from mangrove loss could reach 2391 Tg CO2 eq by the end of the century, or 3392 Tg CO2 eq when considering foregone soil carbon sequestration. The highest emissions were predicted in southeast and south Asia (West Coral Triangle, Sunda Shelf, and the Bay of Bengal) due to conversion to aquaculture or agriculture, followed by the Caribbean (Tropical Northwest Atlantic) due to clearing and erosion, and the Andaman coast (West Myanmar) and north Brazil due to erosion. Together, these six regions accounted for 90% of the total potential CO2 eq future emissions. Mangrove loss has been slowing, and global emissions could be more than halved if reduced loss rates remain in the future. Notably, the location of global emission hotspots was consistent with every dataset used to calculate deforestation rates or with alternative assumptions about carbon storage and emissions. Our results indicate the regions in need of policy actions to address emissions arising from mangrove loss and the drivers that could be managed to prevent them. [ABSTRACT FROM AUTHOR]

Coastal ecosystems are considered environments with great potential for carbon storage. Given the difficulties in quantifying biomass, allometric equations and remote sensing have become fundamental tools in the studies of quantification of vegetation biomass and carbon stocks. Thus, the objective of this study is to quantify and estimate the spatial distribution of vegetation biomass and to quantify the carbon stock of the Parnaíba River Delta vegetation. The study was carried out in part of the Parnaíba River Delta Environmental Protection Area and in the Parnaíba River Delta Marine Extractive Reserve, in NE Brazil, in five spots within distinct vegetation types: psammophile pioneer vegetation, dune subevergreen vegetation, mangrove evergreen vegetation, floodplain vegetation and vegetation associated with carnaubals. At 26 collection points, 10 × 20 m plots were marked, in which the diameter at breast height and height of all individuals were measured. The collected data were used in allometric equations for vegetation biomass estimates and these values were converted into carbon stocks. The spatial distribution of aboveground vegetation biomass (AGB) was also estimated by remote sensing, where we extracted and selected spectral variables obtained from Landsat-8 OLI sensor images, on three different dates. Prediction models were calculated by multiple linear regression analysis. It was observed that the mangrove evergreen vegetation obtained higher vegetation biomass and carbon stock than the others. The models obtained through remote sensing that provided the best estimates of AGB were those of November 12th, 2016 (EAM = 6.84; RMSE = 47.89 Mg ha−1; R2 = 0.72) and November 28th, 2016 (EAM = 9.63; RMSE = 34.67 Mg ha−1; R2 = 0.58). [ABSTRACT FROM AUTHOR]

The soil attributes controlling the CO 2 , and CH 4 emissions were assessed in semiarid mangrove soils (NE-Brazil) under different anthropogenic activities. Soil samples were collected from different mangroves under different anthropogenic impacts, e.g., shrimp farming (Jaguaribe River); urban wastes (Cocó River) and a control site (Timonha River). The sites were characterized according to the sand content; physicochemical parameters (Eh and pH); total organic C; soil C stock (SCS) and equivalent SCS (SCS EQV ); total P and N; dissolved organic C (DOC); and the degree of pyritization (DOP). The CO 2 and CH 4 fluxes from the soils were assessed using static closed chambers. Higher DOC and SCS and the lowest DOP promote greater CO 2 emission. The CH 4 flux was only observed at Jaguaribe which presented higher DOP, compared to that found in mangroves from humid tropical climates. Semiarid mangrove soils cannot be characterized as important greenhouse gas sources, compared to humid tropical mangroves. [ABSTRACT FROM AUTHOR]

Both freshwater floodplain (várzeas and igapós) forests and brackish-saline mangroves are abundant and well-described ecosystems in Brazil. 1 However, an interesting and unique wetland forest exists in the Amazon Delta where extensive mangroves occur in essentially freshwater tidal environments. Unlike the floodplain forests found upriver, the hydrology of these ecosystems is driven largely by large macro-tides of 4–8 m coupled with the significant freshwater discharge from the Amazon River. We explored these mangroves on the Amazon Delta (00°52ʹ N to 01°41ʹ N) and found surface water salinity to be consistently <5; soil pore water salinity in these mangrove forests ranged from 0 nearest the Amazon mouth to only 5–11 at the coastal margins to the north (01°41ʹ N, 49°55′ W). We also recorded a unique mix of mangrove-obligate (Avicennia sp., Rhizophora mangle) and facultative-wetland species (Mauritia flexuosa , Pterocarpus sp.) dominating these forests. This unique mix of plant species and soil porewater chemistry exists even along the coastal strands and active coastlines of the Atlantic Ocean. Part of these unique mangroves have escaped current global satellite mapping efforts, and we estimate that they may add over 180 km2 (20% increase in mangrove area) within the Amazon Delta. Despite having a unique structure and function, these freshwater-brackish ecosystems likely provide similar ecosystem services to most mangroves worldwide, such as sequestering large quantities of organic carbon, protection of shoreline ecosystems from erosion, and habitats to many terrestrial and aquatic species (monkeys, birds, crabs, and fish). • We describe a new forest structure for mangroves in the Amazon Delta • Amazon Delta mangroves thrive in hyposaline and acidic soils • We identified over 180 km2 of previously unmapped forests in the Amazon Delta • These mangroves may hold large coastal carbon stocks Bernardino et al. survey the Amazon Delta and find an unexpected structure and composition of mangroves, where they coexist with trees that are typical of freshwater wetlands. These mangroves were previously unmapped and will have an unprecedented value to climate mitigation and other ecosystem services on this region of the coast. [ABSTRACT FROM AUTHOR]

Seagrasses are found at limited locations in the Eastern Tropical Pacific (ETP). Here, we provide the first characterization of seagrasses at Sámara Bay, on the northern Pacific coast of Costa Rica. Sampling was carried out in August 2018 and March 2019. We measured seagrass biomass, shoot density, leaf area, stable isotope composition (δ13C, δ15N), carbon content, bulk density, and grain size. We also measured water clarity, temperature, dissolved oxygen, salinity, and nutrient concentrations. Two seagrass species were found, Halophila baillonii and Halodule beaudettei , which are commonly found in the ETP. Sediment grain size at Sámara was mostly composed of fine and very fine sand. Total seagrass biomass was 31.9 ± 28.7 g DW m−2 and density was 2136 ± 1576 shoots m−2. Halophila bailloni leaf blade length (1.1 ± 0.3 cm) and width (0.5 ± 0.1 cm) were within ranges for the sizes reported for this species, and were similar to other locations. Halodule beaudettei leaf length (5.0 ± 3.8 cm) and width (0.09 ± 0.02 cm), were larger than at other seagrass meadows on the Pacific coast of Costa Rica yet smaller than in Brazil. Seagrass biomass and density at Sámara were higher in the sampling during the dry season, a pattern also found on the Pacific coast of Costa Rica and in Brazil. We recommend further study of seagrasses at this site and the ETP, including temporal and spatial variability and associated environmental factors. Seagrass presence at Sámara should be considered in local management and conservation initiatives. • This is the first seagrass characterization at Sámara Bay, Costa Rica. • Two seagrass species were found, Halophila baillonii and Halodule beaudettei. • Seagrass diminished in the rainy season, as seen before in Costa Rica and Brazil. • Conservation and management initiatives need to consider protecting seagrasses at Sámara. [ABSTRACT FROM AUTHOR]

The Brazilian government agenda for downgrading and degazettement of protected ecosystems has seen an unprecedented move with the revocation of the mangrove's protection act in the country. As the second largest country in mangrove extent, with over 11,000 km2 of forests that have been conserved for decades, mangroves may now be open for unsustainable economic development. Shrimp aquaculture and urban development are likely the highest threats to mangrove forests in Brazil. When built over mangrove land, shrimp ponds release greenhouse gases at a rate up to 10-fold larger than cattle pasture conversion on dryland forests. In a scenario of low rates of mangrove loss of 0.1% per year (2-fold current rates), emissions from land use would be close to 1.6 Tg CO 2 e per year, which is equivalent to 0.01% of emissions from deforestation in the Amazon over an area 1500 times smaller. Urban development and removal of mangroves to human infrastructure also have strong negative effects on pollutant retention, which could further decrease water quality and increase coastal vulnerability near urban centers. The loss of mangroves have also expected negative effects on food provision, which allied to other key ecosystem services provided by mangroves, will be key to a sustainable ocean under a changing climate during the next century. [ABSTRACT FROM AUTHOR]

• Cananeia-Iguape mangroves store 380 MgC ha−1 in soil and biomass combined. • 70% of ecosystem-level carbon stocks are contained within soils. • Carbon sequestration in soils and biomass and flux via litterfall total 0.16 TgC yr−1. • Degradation of mangroves could lead to the release of 1,395 MgCO 2 ha−1. Mangroves fringe the coastlines of 54% of the world's nations but convey ecosystem services, such as carbon sequestration, that span administrative boundaries. Despite their high carbon sequestration efficiency and long-term storage capacity, few countries have assembled detailed mangrove carbon inventories. For example, Brazil, which detains the second largest mangrove area in the world, still lacks a detailed inventory on its blue carbon resources, largely due to the scarcity of integrated ecosystem-level (that is, carbon stored in biomass and soil combined) carbon assessments. Here we combine published and unpublished data to derive an inventory on ecosystem-level carbon stocks and carbon sequestration rates in the Cananéia-Iguape lagoon estuarine system, southeastern Brazil. We find that mangroves in the study area have the largest per-unit-area ecosystem-level carbon stocks at 380 MgC ha−1 when compared to other Brazilian mangroves. Soil organic carbon stocks (top meter) account for 70% of this total. Annual carbon sequestration in mangrove soils and woody biomass combined with carbon fluxes via litterfall total 0.16 TgC yr−1. Degradation of mangrove ecosystems in this region could lead to CO 2 e emissions up to 1,395 MgCO 2 ha−1 and reduce annual carbon sequestration in soil and biomass combined, and carbon flux via litterfall by 27 and 12 MgCO 2 ha−1 yr−1, respectively. Our results provide coastal wetlands managers and scientists with novel information on mangrove carbon stocks and sequestration rates in the study area, which is useful to strengthen regional blue carbon and potential CO 2 e emission inventories. These estimates can also be used to establish performance measures to inform restoration targets as well as to serve as a baseline for comparison with current and future measurements of carbon stocks and fluxes in response to environmental change. [ABSTRACT FROM AUTHOR]

The Marapanim River estuary (MRE) is part of the Amazon estuarine system located in northern Brazil, which is characterized as having extensive mangrove forests. Given that previous studies reported CO 2 and CH 4 fluxes from mangrove creeks in this region, here we investigate the potential organic carbon sequestration of the creek mudflats to get a better understanding of the carbon cycling through these systems. Sediment accumulation rates derived from 210Pb dating indicated that sampled cores represent the previous 24 (± 4) yr. The approximately 24-year total organic carbon (TOC), total nitrogen (TN) and total phosphorus (TP) burial rates were estimated to be 192.5 (± 43.5), 15.3 (± 4.1) and 3.2 (± 0.8) g m−2 yr−1, respectively. A binary source mixing model based on carbon stable isotopes (δ13C) revealed that the sedimentary organic matter (OM) is mainly influenced by marine phytoplankton input (49% to 95%). Furthermore, the TOC accumulation rates found here were slightly higher than the global averages estimated for within mangrove forests, suggesting that these unaccounted carbon sinks along creek mudflat environments are relevant for carbon budgets in mangrove-colonized coastal zones. The highest contents, stocks and accumulation rates were found in the tidal creek sediments that are most influenced by nearby mangroves and are more protected than sediments from major river margins. Our results indicate that the creek mudflats play a major role in carbon and nutrients sequestration, directly related to grain size and OM sources. • Organic matter (OM) source was mainly influenced by marine OM input (49% to 95%). • Amazon mangrove creeks accumulate large amounts of carbon and nutrients. • OC, N and P contents, stocks and burial depend on the grain size and OM sources. • The capacity to sequester OC increased with increases in TN and TP burial rates. [ABSTRACT FROM AUTHOR]

A persistent challenge to managing coastal wetlands in a way that will mitigate climate impacts is understanding how soil organic carbon (Corg) stocks change over spatial and temporal scales. This study tested how seasonal change in riverine flows and soil biogeochemical attributes (grain-size, degree of wave disturbance and microphytobenthic productivity) can influence the Corg stock estimates of an unvegetated tidal flat within a Brazilian subtropical bay. We used a Generalized Additive Modelling (GAM) approach to accurately predict and map subtle changes in the Corg pools of these expansive, but often overlooked coastal ecosystems. The most important predictors across seasons were sediment grain-size and wave exposure. Seasonally important covariates were riverine flow and microphytobenthic productivity (during the warm and wet summer season). We then compared the high-resolution map outputs derived from models with more traditional approaches (interpolation and extrapolation) to see how these different methods might influence estimates of the carbon stocks for the entire bay (i.e., an area covering 115 ha). Modelled estimates for the bay (1945 ± 45 Mg Corg) where more conservative and had lower associated error than interpolated (2196 ± 185 Mg) and extrapolated estimates (2535 ± 117 Mg). Given the current urgency to understand the carbon sequestration potential of coastal ecosystems, the present findings are important and draw attention to the often overlooked, but important carbon pools of intertidal mudflats. • Measuring soil organic carbon (Corg) stocks is a challenge in coastal environments. • We tested if seasonally variable covariates can help predict Corg pools of mudflats. • Important factors were soil grain-size, waves, river flow & benthic productivity. • Modelled Corg estimates were lower and more accurate than other approaches. • We highlight the variability of carbon pools from unvegetated coastal habitats. [ABSTRACT FROM AUTHOR]

Tree height is a key parameter to accurately quantify above ground biomass (AGB) of trees. Approaches that integrate airborne light detection and ranging (LiDAR) with mapped extents of forests may improve estimation of mangrove heights by providing considerably more measurements of mangrove tree heights than can be achieved using field-based measurements alone. In this study, we present a validated method for quantifying mangrove AGB that was demonstrated for a mangrove forest at Guarás Island, Brazil. The application of LiDAR to estimate mangrove height was confirmed by correlating 89 tree heights measured in the field with LiDAR-derived mangrove heights, resulting in highly robust relationships for Avicennia germinans , Laguncularia racemosa and Rhizophora mangle (R2 = 0.90–0.97, RMSE of 1.24–0.67 m and RMSE% of 11.26%–25.97%). These relationships were used to calibrate a LiDAR-derived canopy height model (CHM) and develop robust relationships between the calibrated-CHM and field-based estimates of AGB (R2 = 0.85–0.92, RMSE of 3.1 kg–42.53 kg, RMSE% of 20.66%–43.81%). This relationship was then applied to the CHM whilst accounting for tree density to estimate mangrove AGB. Total mangrove AGB per hectare was estimated to be 246.90 t ha−1, corresponding closely with previous mangrove AGB measurements within the region. This study found that mangrove height and AGB are statistically related and these relationships can be applied to allometric equations for specific species to improve mangrove AGB estimates. This study demonstrates the capacity for LiDAR-derived tree heights to replace traditional approaches to estimating AGB and improving estimates of mangrove blue carbon storage. Application of LiDAR to determine tree heights will be particularly useful where mangrove is extensive and/or remote. Image 1 • Mangrove height and AGB are statistically related. • Lidar derived mangrove heights can improve biomass and carbon storage estimates. • Amazonian mangrove biomass was estimated by correlating tree biomass with Lidar. • Individual tree biomass was corrected for density using mangrove plot density data. • This approach improves biomass estimates where fieldwork can be difficult. [ABSTRACT FROM AUTHOR]