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The Legal Amazon of Brazil holds vast mangrove forests, but a lack of awareness of their value has prevented their inclusion into results-based payments established by the United Nations Framework Convention on Climate Change. Based on an inventory from over 190 forest plots in Amazon mangroves, we estimate total ecosystem carbon stocks of 468 ± 67 Megagrams (Mg) ha−1; which are significantly higher than Brazilian upland biomes currently included into national carbon offset financing. Conversion of mangroves results in potential emissions of 1228 Mg CO2e ha−1, which are 3-fold higher than land use emissions from conversion of the Amazon rainforest. Our work provides the foundation for the inclusion of mangroves in Brazil's intended Nationally Determined Contribution, and here we show that halting mangrove deforestation in the Legal Amazon would generate avoided emissions of 0.9 ± 0.3 Teragrams (Tg) CO2e yr−1; which is equivalent to the annual carbon accumulation in 82,400 ha of secondary forests. A new study shows that deforestation of Amazon mangroves releases up to four times more carbon dioxide when compared to emissions arising from terrestrial biomes. This study set a foundation for the use of mangroves in Brazil's international policy agreements. [ABSTRACT FROM AUTHOR]

Crab and soil samples were seasonally collected at four mangrove sites (Cacha Prego, CP; Ponta Grossa, PG; Ilha de Maré, IM; and Pitinga, PT) in Todos os Santos Bay, in NE Brazil. Total Cu levels in soils ranged from 2.5 to 89.4 mg kg−1, while in crab organs (muscles, hepatopancreas, and gills), Cu ranged from 20 to 1,320 mg kg−1, with the highest concentrations found in the Ilha de Maré population, where soils showed a clear Cu enrichment. Total Cu content did not explain the abnormally high Cu concentrations observed in crabs from Pitinga, where total content in soil was low. Geochemical partitioning indicated that most of the potentially bioavailable Cu was found in the oxidizable fractions, pyrite and organic matter. Pyrite oxidation during the dry season led to increased Cu bioavailability. This process was of relevance in soils of the Pitinga mangrove, where sulfide oxidation led to soil acidification and to an increase in Cu associated with the most labile fractions. [ABSTRACT FROM AUTHOR]

The potential of Blue Carbon as an integral part of global climate change adaptation and mitigation strategies requires quantification of drivers and rates of organic carbon (OC) burial and storage. However, there is limited recognition of how land use impacts benthic assemblages, their bioturbation potential, and OC burial in mangrove forests and tidal flats. Here we evaluated the effects of mangrove deforestation on benthic bioturbation potential (BPc), sediment accretion rates (SARs), and OC and total nitrogen (TN) burial in mangrove soils and tidal flat sediments from three estuaries in tropical Brazil. SARs based on 210Pb dating varied significantly among undisturbed estuaries (2.1–18.6 mm yr−1) and the OC and TN burial rates were respectively 46% and 16% higher than global averages. The cleared mangrove sites had a twofold lower SAR, 40‐fold lower OC burial, and over 100‐fold lower TN burial when compared to undisturbed forests, revealing the pervasive impacts of land use. Variation in benthic assemblage structure and BPc among sites suggests that the composition and activity of macrofaunal communities may facilitate OC burial in some cases, yet the global extent and significance of bioturbation requires further study. Our work reveals a strong spatial variability in C burial in undisturbed mangrove forests and a decreased capacity of mangroves to accumulate C and sediments due to land use effects. [ABSTRACT FROM AUTHOR]

Mangroves sequester large quantities of carbon (C) that become significant sources of greenhouse gases when disturbed through land‐use change. Thus, they are of great value to incorporate into climate change adaptation and mitigation strategies. In response, a global network of mangrove plots was established to provide policy‐relevant ecological data relating to interactions of mangrove C stocks with climatic, tidal, plant community, and geomorphic factors. Mangroves from 190 sites were sampled across five continents encompassing large biological, physical, and climatic gradients using consistent methodologies for the quantification of total ecosystem C stocks (TECS). Carbon stock data were collected along with vegetation, physical, and climatic data to explore potential predictive relationships. There was a 28‐fold range in TECS (79–2,208 Mg C/ha) with a mean of 856 ± 32 Mg C/ha. Belowground C comprised an average 85% of the TECS. Mean soil depth was 216 cm, ranging from 22 to >300 cm, with 68 sites (35%) exceeding a depth of 300 cm. TECS were weakly correlated with metrics of forest structure, suggesting that aboveground forest structure alone cannot accurately predict TECS. Similarly, precipitation was not a strong predictor of TECS. Reasonable estimates of TECS were derived via multiple regression analysis using precipitation, soil depth, tree mass, and latitude (R2 = 0.54) as variables. Soil carbon to a 1 m depth averaged 44% of the TECS. Limiting analyses of soil C stocks to the top 1 m of soils result in large underestimates of TECS as well as in the greenhouse gas emissions that would arise from their conversion to other land uses. The current IPCC Tier 1 default TECS value for mangroves is 511 Mg C/ha, which is only 60% of our calculated global mean. This study improves current assessments of mangrove C stocks providing a foundation necessary for C valuation related to climate change mitigation. We estimate mangroves globally store about 11.7 Pg C: an aboveground carbon stock of 1.6 Pg C and a belowground carbon stock of 10.2 Pg C). The differences in the estimates of total ecosystem carbon stocks based on climate, salinity, forest structure, geomorphology, or geopolitical boundaries are not as much of an influence as the choice of soil depth included in the estimate. Choosing to limit soils to a 1 m depth resulted in estimates of <5 Pg whereas those that included the soil profile >1 m depth resulted in global carbon stock estimates that exceeded 11.2 Pg C. [ABSTRACT FROM AUTHOR]

Seasonality and crab activity affects the nutrients and physicochemical parameters in mangrove soils, thus, affecting the emissions of greenhouse gases, such as nitrous oxide (N2O). Climate change may intensify rainfall and/or enhance droughts, affecting mangroves and associated biota. Crabs are natural soil bioturbators responsible for soil aeration and turnover. We evaluated the effect of Ucides cordatus crab on N2O emissions from mangrove soils under a semiarid climate in Northeastern Brazil. Soil and gas samples were collected over the rainy and dry seasons in crab-naturally-bioturbated and crab-exclusion mangrove plots. We measured the soil's pH, redox potential, and the total contents of carbon, nitrogen, and sulfur. We found higher N2O emissions in the crab-exclusion sites compared to the bioturbated sites, as well as higher N2O emissions in the rainy season compared to the dry season. The fluxes of N2O (µg m−2 h−1) were 47.3 ± 9.7 and 8.9 ± 0.5 for the crab-exclusion sites, and 36.5 ± 7.8 and 4.5 ± 2.1 for the bioturbated sites (wet and dry seasons, respectively). The soil turning over by macrofauna led to lower N2O fluxes in natural crab-bioturbated areas, and seasonality was the environmental factor that contributed the most to the changes in N2O emissions. Broadly, anthropic activities and seasonality influence nitrogen fate, N2O emissions, and ecological services in coastal ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Mangroves of the semiarid Caatinga region of northeastern Brazil are being rapidly converted to shrimp pond aquaculture. To determine ecosystem carbon stocks and potential greenhouse gas emissions from this widespread land use, we measured carbon stocks of eight mangrove forests and three shrimp ponds in the Acaraú and Jaguaribe watersheds in Ceará state, Brazil. The shrimp ponds were paired with adjacent intact mangroves to ascertain carbon losses and potential emissions from land conversion. The mean total ecosystem carbon stock of mangroves in this semiarid tropical landscape was 413 ± 94 Mg C/ha. There were highly significant differences in the ecosystem carbon stocks between the two sampled estuaries suggesting caution when extrapolating carbon stock across different estuaries even in the same landscape. Conversion of mangroves to shrimp ponds resulted in losses of 58%–82% of the ecosystem carbon stocks. The mean potential emissions arising from mangrove conversion to shrimp ponds was 1,390 Mg CO2e/ha. Carbon losses were largely from soils which accounted for 81% of the total emission. Losses from soils >100 cm in depth accounted for 33% of the total ecosystem carbon loss. Soil carbon losses from shrimp pond conversion are equivalent to about 182 years of soil carbon accumulation. Losses from mangrove conversion are about 10‐fold greater than emissions from conversion of upland tropical dry forest in the Brazilian Caatinga underscoring the potential value for their inclusion in climate change mitigation activities. [ABSTRACT FROM AUTHOR]

The assessment of the soil organic carbon (SOC) stocks in mangrove ecosystems is essential for coastal management activities seeking the mitigation of CO2 emissions. However, the wet chemical analysis conventionally used to quantify SOC may overestimate SOC content due to oxidation of reduced compounds. This work focused on the use of diffuse reflectance spectroscopy (DRS) for predicting SOC in mangrove forest areas. When used properly, DRS may be, in some cases, a more accurate and more efficient method for the determination of SOC in mangrove soils than conventional analytical approaches. Furthermore, variable selection may simplify and improve prediction accuracy, reducing collinearity in the dataset used and allowing better SOC quantification through more interpretable and robust models. [ABSTRACT FROM AUTHOR]

Pore-water and solid-phase analysis was undertaken to study the effects of different environmental conditions on redox processes in mangrove soils on the southern coast of Brazil. Three Rhizophora mangle (L.) mangrove forests were studied in different physiographic positions-riverine, fringe, and basin forest-and substrate compositions. Our results indicate different geochemical conditions in soils from different physiographic positions. In the fringe soils, the low acid-volatile sulfide and pyrite Fe contents, associated with high values of Fe2+ in pore water, indicate oxic and suboxic conditions in surface layers (0-10 cm). Below this depth, anoxic conditions prevail and sulfate reduction becomes the dominant process of organic matter decay, as indicated by higher concentrations of dissolved HS and pyrite Fe. In the basin forest, long periods of tidal flooding and low rates of litter export maintained anoxic conditions and high organic matter contents, necessary for anoxic respiration to take place, as shown by the low Fe2+ and HS- concentrations in pore water, along with high degree of Fe pyritization values and high concentrations of pyrite Fe. In the riverine soils, the lowest concentrations of pyrite Fe and the highest concentrations of HSin pore water were obtained in response to low availability of reactive Fe (0-10cm, 31.8 ± 8.0 mmol kg-1; 20-30 cm, 43.2 ± 32.3 mmol kg-1) due to its sandy texture, which limits pyrite synthesis. Our results indicate that the participation and intensity of each process may vary within different physiographic positions because of the effects on the frequency and duration of tidal flooding and soil composition. Our results also show that R. mangle is present on substrates with different geochemical conditions (oxic, suboxic, and anoxic). [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]

Drought events may induce mangrove mortality and dieback events worldwide as a result of climate extremes. As mangroves sequester large quantities of carbon, quantifying the losses of these stocks following climate disturbances may guide wetland governance strategies globally. In Southeast Brazil, we determined the total ecosystem carbon stocks (TECS) of pristine mangroves that were up to 1851 Mg of carbon per hectare (Mg C ha−1), which are the highest stocks measured from South American and raising estimates of Brazil's mangrove TECS to 0.52 Pg C. A mangrove mortality event in the same estuary resulted in a 14.6 % decrease in TECS (270.5 Mg C ha−1) and loss of 20 % of mangrove soil carbon within less than 2-years. Carbon dioxide emissions from this impact were 992.8 Mg CO 2 e ha−1, which are slightly lower than emissions from land use disturbances on mangroves worldwide. Our results suggest that climate effects on mangroves can become significant sources of greenhouse gases globally. [Display omitted] • The pristine mangroves in SE Brazil stock over 1851 Mg C ha−1. • Climate-relate impacts resulted in 14.6 % decrease in total ecosystem carbon stock. • The mangrove dieback lead to 40.4 % of carbon losses on the 0–30 cm soil. • Carbon dioxide emissions from the climate-relate impact was 992.8 Mg CO 2 e ha−1. • The Brazilian mangroves hold 5 % (0.52 Pg C) of the global mangrove ecosystem stock. [ABSTRACT FROM AUTHOR]