How do replanted mangroves affect phosphorus dynamics in their soils?

Phosphorus is a limiting element for the productivity of mangroves, which in turn are important ecosystems in regulating nutrients cycle and climate change by sequestering carbon (C). Despite this, there is an intense process of degradation in these environments. In addition to providing socio-environmental services, mangrove replanting can also alter the dynamics of nutrients in soils. Therefore, this study aims to understand the changes in soil phosphorus (P) fractions after a mangrove restoration. Soil samples from an unvegetated area (NV), a mature mangrove (R) and 7 and 9 year old replanted mangroves at SE-Brazil (APA Guapi-mirim, Rio de Janeiro state) were collected and analyzed to characterize the redox conditions (Eh), pH, and iron (Fe) fractionation, Total Organic Carbon (TOC) contents and P fractionation (exchangeable P; P associated with reducible Fe and Mn oxyhydroxides; associated with Al silicates and hydroxides; associated with humic acids; associated with Ca and Mg; associated with humin). The results indicate an increase in TOC as the age of the mangrove restoration increases (from 8.6 to 17.9%). The pH values were significantly lower, reaching very acidic values, associated with an increase in Eh. Both parameters also showed strong seasonal variation, with a drop in Eh during the wet period (from 165% to -46%) and an increase in pH in the same period (from 6.0 to 6.7). Regarding P fractionation, the main P pool was organic P forms, which showed the highest concentrations in all studied sites. Unvegetated areas showed higher organic P forms (NV: 108.8 µg g-1) than vegetated areas (M7: 55.7 µg g-1, M9: 83.6 µg g-1, R: 87.3 µg g-1). Vegetated sites also showed lower levels of the PEx, PFeMn and Papatite fractions (total forest mean: 2.4 µg g-1, 5.8 µg g-1, 3.0 µg g-1, respectively). Besides no clear trend on P fractionation through seasons and forest age, pseudo-total P increased following the forest recovery (e.g. M7

Soil greenhouse gas emissions from dead and natural mangrove forests in Southeastern Brazil.

Mangroves forests may be important sinks of carbon in coastal areas but upon their death, these forests may become net sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere. Here we assessed the spatial and temporal variability in soil CO2 and CH4 fluxes from dead mangrove forests and paired intact sites in SE-Brazil. Our findings demonstrated that during warmer and drier conditions, CO2 soil flux was 183 % higher in live mangrove forests when compared to the dead mangrove forests. Soil CH4 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 CO2e ha-1 y-1. Overall, we found that dead mangroves did not release great amounts of GHG after three years of forest loss.

Terrestrial inputs boost organic carbon accumulation in Mexican mangroves.

Despite their ability to mitigate climate change by efficiently absorbing atmospheric carbon dioxide (CO2) and acting as natural long-term carbon sinks, mangrove ecosystems have faced several anthropogenic threats over the past century, resulting in a decline in the global mangrove cover. By using standardized methods and the most recent Bayesian tracer mixing models MixSIAR, this study aimed to quantify source contributions, burial rates, and stocks of organic carbon (Corg) and explore their temporal changes (∼100 years) in seven lead-210 dated sediment cores collected from three contrasting Mexican mangrove areas. The spatial variation in Corg burial rates and stocks in these blue carbon ecosystems primarily depended on the influence of local rivers, which controlled Corg sources and fluxes within the mangrove areas. The Corg burial rates in the cores ranged from 66 ± 16 to 400 ± 40 g m-2 yr-1. The Corg stocks ranged from 84.9 ± 0.7 to 255 ± 2 Mg ha-1 at 50 cm depth and from 137 ± 2 to 241 ± 4 Mg ha-1 at 1 m depth. The highest Corg burial rates and stocks were observed in cores from the carbonate platform of Yucatan and in cores with reduced river influence and high mangrove detritus inputs, in contrast to patterns identified from global databases. Over the past century, the rising trends in Corg burial rates and stocks in the study sites were primarily driven by enhanced inputs of fluvial-derived Corg and, in some cores, mangrove-derived Corg. Despite their decreasing extension, mangrove areas remained highly effective producers and sinks of Corg. Ongoing efforts to enhance the global database should continue, including mangrove area characteristics and reliable timescales to facilitate cross-comparison among studies.

Carbon stock estimation in a Brazilian mangrove using optical satellite data.

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.

Belize Blue Carbon: Establishing a national carbon stock estimate for mangrove ecosystems.

Mangrove ecosystems are among the most economically and ecologically valuable marine environments in the world. Mangroves are effective at long-term carbon storage within their sediments and are estimated to hold 12 billion metric tons of carbon worldwide. These ecosystems are therefore vitally important for carbon sequestration and, by extension, climate change mitigation. As part of the Paris Agreement, participating countries agree to provide plans to reduce their carbon emissions, or nationally determined contributions (NDCs). However, despite mangroves being recognized as important nature-based solutions, many countries still lack national data on carbon stocks and must use global or regional averages, which may not be sufficiently accurate. Here, we present the national carbon stock estimate of mangrove ecosystems for the NDC of Belize, acquired through a collaborative approach involving government agencies and NGOs. We conducted a comprehensive sampling of mangroves across the country, including a range of mangrove ecotypes. The mean total ecosystem carbon stock (TECS) for the nation was 444.1 ± 21.0 Mg C ha-1, with 74.4 ± 6.2 Mg C ha-1 in biomass stocks, and 369.7 ± 17.7 Mg C ha-1 in sediment stocks. Combining these data with a recent mapping effort, we provide the first national comprehensive mangrove carbon stock estimate of 25.7 Tg C. The national mean from this study varies from previous global analyses, which can under- or overestimate TECS by as much as 0.6 Tg C and 16.5 Tg C, respectively, depending on the study. These data supported the NDC update of Belize, and can be used to inform the country's mangrove protection and restoration commitments. The collaborative approach of this work should serve as a blueprint for other countries seeking to conserve natural blue carbon sinks as a strategy to achieve their climate targets.

Mangrove microbial community recovery and their role in early stages of forest recolonization within shrimp ponds.

Shrimp farming is blooming worldwide, posing a severe threat to mangroves and its multiple goods and ecosystem services. Several studies reported the impacts of aquaculture on mangrove biotic communities, including microbiomes. However, little is known about how mangrove soil microbiomes would change in response to mangrove forest recolonization. Using genome-resolved metagenomics, we compared the soil microbiome of mangrove forests (both with and without the direct influence of shrimp farming effluents) with active shrimp farms and mangroves under a recolonization process. We found that the structure and composition of active shrimp farms microbial communities differ from the control mangrove forests, mangroves under the impact of the shrimp farming effluents, and mangroves under recolonization. Shrimp farming ponds microbiomes have lower microbial diversity and are dominated by halophilic microorganisms, presenting high abundance of multiple antibiotic resistance genes. On the other hand, control mangrove forests, impacted mangroves (exposed to the shrimp farming effluents), and recolonization ponds were more diverse, with a higher abundance of genes related to carbon mobilization. Our data also indicated that the microbiome is recovering in the mangrove recolonization ponds, performing vital metabolic functions and functionally resembling microbiomes found in those soils of neighboring control mangrove forests. Despite highlighting the damage caused by the habitat changes in mangrove soil microbiome community and functioning, our study sheds light on these systems incredible recovery capacity. Our study shows the importance of natural mangrove forest recovery, enhancing ecosystem services by the soil microbial communities even in a very early development stage of mangrove forest, thus encouraging mangrove conservation and restoration efforts worldwide.

Seagrass contribution to blue carbon in a shallow karstic coastal area of the Gulf of Mexico.

Seagrass meadows provide multiple ecosystem services, including carbon sequestration. However, seagrass meadows are among the most threatened ecosystems worldwide. Determining the magnitude of the carbon stocks in seagrass meadows at the regional scale allows for the estimation of their global magnitude and identification of their importance in regional environmental mitigation strategies. The objective of the present study was to determine the structure of seagrass meadows in the Los Petenes Biosfera Reserve (LPBR) and evaluate their contributions to sinks of carbon in this system, located in Yucatan, which is considered the region with the largest seagrass extension in Mexico. Analyses of the seagrass meadows were executed following standardized protocols (spectral analysis, and isotope and carbon stock analyses). The LPBR stores an average of 2.2 ± 1.7 Mg C ha-1 in living biomass and 318 ± 215 Mg C ha-1 in sediment (top 1 m), and this carbon stock decreases with water depth. The seagrass community extends 149,613 ha, which represents the largest organic carbon stock (47 Tg C) documented in seagrass meadows in Mexico. Macroalgae and seagrass represent 76% of the organic carbon stored in sediment. If LPBR seagrass meadows are lost due to natural or anthropogenic impacts, 173 Tg CO2eqemissions could be released, which corresponds to the emissions generated by fossil fuel combustion of 27% of the current Mexican population. This information emphasizes the importance of seagrass meadows as a carbon sink in the region and their contribution to climate change mitigation, thus allowing for the implementation of necessary conservation strategies.

Brazilian Semi-Arid Mangroves-Associated Microbiome as Pools of Richness and Complexity in a Changing World.

Mangrove microbiomes play an essential role in the fate of mangroves in our changing planet, but the factors regulating the biogeographical distribution of mangrove microbial communities remain essentially vague. This paper contributes to our understanding of mangrove microbiomes distributed along three biogeographical provinces and ecoregions, covering the exuberant mangroves of Amazonia ecoregion (North Brazil Shelf) as well as mangroves located in the southern limit of distribution (Southeastern ecoregion, Warm Temperate Southwestern Atlantic) and mangroves localized on the drier semi-arid coast (Northeastern ecoregion, Tropical Southwestern Atlantic), two important ecotones where poleward and landward shifts, respectively, are expected to occur related to climate change. This study compared the microbiomes associated with the conspicuous red mangrove (Rhizophora mangle) root soils encompassing soil properties, latitudinal factors, and amplicon sequence variants of 105 samples. We demonstrated that, although the northern and southern sites are over 4,000 km apart, and despite R. mangle genetic divergences between north and south populations, their microbiomes resemble each other more than the northern and northeastern neighbors. In addition, the northeastern semi-arid microbiomes were more diverse and displayed a higher level of complexity than the northern and southern ones. This finding may reflect the endurance of the northeast microbial communities tailored to deal with the stressful conditions of semi-aridity and may play a role in the resistance and growing landward expansion observed in such mangroves. Minimum temperature, precipitation, organic carbon, and potential evapotranspiration were the main microbiota variation drivers and should be considered in mangrove conservation and recovery strategies in the Anthropocene. In the face of changes in climate, land cover, biodiversity, and chemical composition, the richness and complexity harbored by semi-arid mangrove microbiomes may hold the key to mangrove adaptability in our changing planet.

Soil Organic Matter Responses to Mangrove Restoration: A Replanting Experience in Northeast Brazil.

Mangroves are among the most relevant ecosystems in providing ecosystem services because of their capacity to act as sinks for atmospheric carbon. Thus, restoring mangroves is a strategic pathway for mitigating global climate change. Therefore, this study aimed to examine the organic matter dynamics in mangrove soils during restoration processes. Four mangrove soils under different developmental stages along the northeastern Brazilian coast were studied, including a degraded mangrove (DM); recovering mangroves after 3 years (3Y) and 7 years (7Y) of planting; and a mature mangrove (MM). The soil total organic carbon (CT) and soil carbon stocks (SCSs) were determined for each area. Additionally, a demineralization procedure was conducted to assess the most complex humidified and recalcitrant fractions of soil organic matter and the fraction participating in organomineral interactions. The particle size distribution was also analyzed. Our results revealed significant differences in the SCS and CT values between the DM, 3Y and 7Y, and the MM, for which there was a tendency to increase in carbon content with increasing vegetative development. However, based on the metrics used to evaluate organic matter interactions with inorganic fractions, such as low rates of carbon enrichment, C recovery, and low C content after hydrofluoric acid (HF) treatment being similar for the DM and the 3Y and 7Y-this indicated that high carbon losses were coinciding with mineral dissolution. These results indicate that the organic carbon dynamics in degraded and newly planted sites depend more on organomineral interactions, both to maintain their previous SCS and increase it, than mature mangroves. Conversely, the MM appeared to have most of the soil organic carbon, as the stabilized organic matter had a complex structure with a high molecular weight and contributed less in the organomineral interactions to the SCS. These results demonstrate the role of initial mangrove vegetation development in trapping fine mineral particles and favoring organomineral interactions. These findings will help elucidate organic accumulation in different replanted mangrove restoration scenarios.

Future carbon emissions from global mangrove forest loss.

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.

Blue carbon of Mexico, carbon stocks and fluxes: a systematic review.

Mexico has more than 750,000 ha of mangroves and more than 400,000 ha of seagrasses. However, approximately 200,000 ha of mangroves and an unknown area of seagrass have been lost due to coastal development associated with urban, industrial and tourist purposes. In 2018, the approved reforms to the General Law on Climate Change (LGCC) aligned the Mexican law with the international objectives established in the 2nd Article of the Paris Agreement. This action proves Mexico's commitment to contributing to the global target of stabilizing the greenhouse gas emissions concentration in the planet. Thus, restoring and conserving mangrove and seagrass habitats could contribute to fulfilling this commitment. Therefore, as a first step in establishing a mitigation and adaptation plan against climate change with respect to conservation and restoration actions of these ecosystems, we evaluated Mexican blue carbon ecosystems through a systematic review of the carbon stock using the standardized method of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We used the data from 126 eligible studies for both ecosystems (n = 1220). The results indicated that information is missing at the regional level. However, the average above and below ground organic carbon stocks from mangroves in Mexico is 113.6 ± 5.5 (95% CI [99.3-118.4]) Mg Corg ha-1 and 385.1 ± 22 (95% CI [344.5-431.9]) Mg Corg ha-1, respectively. The variability in the Corg stocks for both blue carbon ecosystems in Mexico is related to variations in climate, hydrology and geomorphology observed along the country's coasts in addition to the size and number of plots evaluated with respect to the spatial cover. The highest values for mangroves were related to humid climate conditions, although in the case of seagrasses, they were related to low levels of hydrodynamic stress. Based on the official extent of mangrove and seagrass area in Mexico, we estimate a total carbon stock of 237.7 Tg Corg from mangroves and 48.1 Tg Corg from seagrasses. However, mangroves and seagrasses are still being lost due to land use change despite Mexican laws meant to incorporate environmental compensation. Such losses are largely due to loopholes in the legal framework that dilute the laws' effectiveness and thus ability to protect the ecosystem. The estimated emissions from land use change under a conservative approach in mangroves of Mexico were approximately 24 Tg CO2e in the last 20 years. Therefore, the incorporation of blue carbon into the carbon market as a viable source of supplemental finance for mangrove and seagrass protection is an attractive win-win opportunity.

Prioritizing mangrove conservation across Mexico to facilitate 2020 NDC ambition.

There is a scale mismatch between mangrove conservation and carbon emission mitigation policies despite mangroves contributing disproportionally to global carbon sequestration. Using Mexico as a case study in the integration of these scales, we estimate mangrove carbon value and deforestation rates at the municipio (local government) scale and develop a prioritization model that indicates where to focus conservation efforts. By using previously published global models of carbon stocks, Mexico-specific carbon sequestration data, and calculating gross deforestation, we found that the current rate of deforestation will result in a social cost of 392.0 (± 7.4) million US$ over the next 25 years. The prioritization model identified 26 municipios of 175, where if all mangroves are conserved, 50% of this cost could be avoided. Bridging the gap between research and governmental action using local initiatives will be paramount for the effective management of mangrove carbon.

Relevance of carbon burial and storage in two contrasting blue carbon ecosystems of a north-east Pacific coastal lagoon.

Coastal vegetated ecosystems constitute very productive habitats, characterized by efficient Corg sequestration and long-term preservation in sediments, so they play an important role in climate change mitigation. The temporal evolution of Corg content, stocks and burial rates were evaluated in seagrass and salt marsh habitats in San Quintin Bay (northeast Pacific, Mexico) by using 210Pb-dated sediment cores. Salt marsh cores were characterized by fine-grained sediments, higher salinities, lower terrigenous input and lower mass accumulation rates (MAR: 0.01-0.03 g cm-2 yr-1) than seagrass cores (MAR: 0.02-3.21 g cm-2 yr-1). Accumulation rates in both habitats steadily increased throughout the past century most likely because of soil erosion promoted by land use changes in the surroundings. The Corg stocks were highest in salt marsh cores (12.2-53.6 Mg ha-1 at 10 cm depth; 259-320 Mg ha-1 at 1 m depth) than in seagrass cores (5.7-14.4 Mg ha-1, and 80-98, Mg ha-1, respectively), whereas Corg burial rates were considerably lower in salt marsh (13-60 g m-2 yr-1) than in seagrass (9-144 g m-2 yr-1) habitats, and the temporal variations observed in Corg burial rates were mostly driven by changes in the accumulation rates. The overall Corg stock (485 ±â€¯51 Gg C) for both habitats together was comparable to the carbon emissions of a major city nearby. Our results highlight the need to protect these environments as relevant carbon reservoirs.

Gulf of Mexico estuarine blue carbon stock, extent and flux: Mangroves, marshes, and seagrasses: A North American hotspot.

The Gulf of Mexico blue carbon habitats (mangroves, seagrass, and salt marshes) form an important North American blue carbon hot spot. These habitats cover 2,161,446 ha and grow profusely in estuaries that occupy 38,000 km2 to store substantial sedimentary organic carbon of 480.48 Tg C. New investigations around GoM for Mexican mangroves, Louisiana salt marshes and seagrasses motivated our integration of buried organic carbon to elucidate a new estimate of GoM blue carbon stocks. Factors creating this include: large GoM watersheds enriching carbon slowly flowing through shallow estuarine habitats with long residence times; fewer SE Mexican hurricanes allowing enhanced carbon storage; mangrove carbon productivity enhanced by warm southern basin winter temperatures; large Preservation reserves amongst high anthropogenic development. The dominant total GoM mangrove blue carbon stock 196.88 Tg from total mangrove extent 650,482 ha is highlighted from new Mexican data. Mexican mangrove organic carbon stock is 112.74 Tg (1st sediment meter) plus USA 84.14 Tg. Mexican mangroves vary greatly in storage, total carbon depositional depths and in sediment age (to 3500 y). We report Mexican mangrove's conservative storage fraction for the normally-compared top meter, whereas the full storage depth estimates ranging above 366.78 Tg (high productivity in very deep sediment along the central Veracruz/Tabasco coast) are not reflected in our reported estimates. Seagrasses stock of 184.1 Tg C organic is derived from 972,327 ha areal extent (in 1st meter). The Louisiana marshes form the heart of GoM salt marsh carbon storage 99.5 Tg (in 1st meter), followed by lesser stocks in Florida, Texas, finally Mexico derived from salt marsh extent totaling 650,482 ha. Constraints on the partial estuarine fluxes given for this new data are discussed as well as widespread anthropogenic destruction of the GoM blue carbon. A new North American comparison of our GoM blue carbon stocks versus Atlantic coastal blue carbon stock estimates is presented.

The value of information: Realising the economic benefits of mapping seagrass meadows in the British Virgin Islands.

Carbon capturing coastal and marine habitats around the world are decreasing in extent every year, habitats found in abundance in Small Island Developing States' territories. However, these habitats are under threat by increased levels of economic activities and extreme weather events. Consequently, as those ecosystems become scarce their value is expected to increase. In this paper the "value of information", the increase in knowledge that renders a system or a function more valuable, from marine habitat mapping is presented through the (monetary) valuation of one regulating service provided by the newly mapped habitats. Mapping a section of a channel with a multibeam echosounder revealed more seagrass resources than in previous studies. Using values for both the Social Cost of Carbon and Abatement Cost methods, from the literature we estimate the value of the carbon sequestration and storage service these seagrass meadows provide. The impacts of hurricanes in the newly mapped seagrasses were also investigated. Despite the costs of mapping, monitoring and of projected losses of ecosystem services provision due to hurricanes, net benefits over a time period of 50 years were considerably larger. The new information provided highlights carbon capturing habitats as more important, enabling the "value of information" to inform policymaking.

Factors influencing organic carbon accumulation in mangrove ecosystems.

There is growing interest in the capacity of mangrove ecosystems to sequester and store 'blue carbon'. Here, we provide a synthesis of 66 dated sediment cores with previously calculated carbon accumulation rates in mangrove ecosystems to assess the effects of environmental and anthropogenic pressures. Conserved sedimentary environments were found to be within the range of the current global average for sediment accretion (approx. 2.5 mm yr-1) and carbon accumulation (approx. 160 g m-2 yr-1). Moreover, similar sediment accretion and carbon accumulation rates were found between mixed and monotypic mangrove forests, however higher mean and median values were noted from within the forest as compared to adjacent areas such as mudflats. The carbon accumulation within conserved environments was up to fourfold higher than in degraded or deforested environments but threefold lower than those impacted by domestic or aquaculture effluents (more than 900 g m-2 yr-1) and twofold lower than those impacted by storms and flooding (more than 500 g m-2 yr-1). These results suggest that depending on the type of impact, the blue carbon accumulation capacity of mangrove ecosystems may become substantially modified.

Carbon stocks of mangroves and salt marshes of the Amazon region, Brazil.

In addition to the largest existing expanse of tropical forests, the Brazilian Amazon has among the largest area of mangroves in the world. While recognized as important global carbon sinks that, when disturbed, are significant sources of greenhouse gases, no studies have quantified the carbon stocks of these vast mangrove forests. In this paper, we quantified total ecosystem carbon stocks of mangroves and salt marshes east of the mouth of the Amazon River, Brazil. Mean ecosystem carbon stocks of the salt marshes were 257 Mg C ha-1 while those of mangroves ranged from 361 to 746 Mg C ha-1 Although aboveground mass was high relative to many other mangrove forests (145 Mg C ha-1), soil carbon stocks were relatively low (340 Mg C ha-1). Low soil carbon stocks may be related to coarse textured soils coupled with a high tidal range. Nevertheless, the carbon stocks of the Amazon mangroves were over twice those of upland evergreen forests and almost 10-fold those of tropical dry forests.

Shrimp ponds lead to massive loss of soil carbon and greenhouse gas emissions in northeastern Brazilian mangroves.

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.

High heterogeneity in soil composition and quality in different mangrove forests of Venezuela.

Mangrove forests play an important role in biogeochemical cycles of metals, nutrients, and C in coastal ecosystems. However, these functions could be strongly affected by the mangrove soil degradation. In this study, we performed an intensive sampling characterizing mangrove soils under different types of environment (lagoon/gulf) and vegetation (Rhizophora/Avicennia/dead mangrove) in the Venezuelan coast. To better understand the spatial heterogeneity of the composition and characteristics of the soils, a wide range of the soil attributes were analyzed. In general, the soils were anoxic (Eh < 200 mV), with a neutral pH and low concentration in toxic metals; nevertheless, they varied widely in the soil and its quality-defining parameters (e.g., clay contents, total organic carbon, Fe, Al, toxic trace metals). It is noteworthy that the mangroves presented a low FePyrite content due to a limitation in the Fe oxyhydroxide contents, especially in soils with higher organic C content (TOC > 15%). Finally, the dead mangrove showed significantly lower amounts of TOC and fibers (in comparison to the well-preserved mangrove forest), which indicates that the C pools in mangrove soils are highly sensitive also to natural impact, such as ENSO.

Seagrass blue carbon dynamics in the Gulf of Mexico: Stocks, losses from anthropogenic disturbance, and gains through seagrass restoration.

Seagrasses comprise a substantive North American and Caribbean Sea blue carbon sink. Yet fine-scale estimates of seagrass carbon stocks, fluxes from anthropogenic disturbances, and potential gains in sedimentary carbon from seagrass restoration are lacking for most of the Western Hemisphere. To begin to fill this knowledge gap in the subtropics and tropics, we quantified organic carbon (Corg) stocks, losses, and gains from restorations at 8 previously-disturbed seagrass sites around the Gulf of Mexico (GoM) (n=128 cores). Mean natural seagrass Corg stocks were 25.7±6.7MgCorgha-1 around the GoM, while mean Corg stocks at adjacent barren sites that had previously hosted seagrass were 17.8MgCorgha-1. Restored seagrass beds contained a mean of 38.7±13.1MgCorgha-1. Mean Corg losses differed by anthropogenic impact type, but averaged 20.98±7.14MgCorgha-1. Corg gains from seagrass restoration averaged 20.96±8.59Mgha-1. These results, when combined with the similarity between natural and restored Corg content, highlight the potential of seagrass restoration for mitigating seagrass Corg losses from prior impact events. Our GoM basin-wide estimates of natural Corg totaled ~36.4Tg for the 947,327ha for the USA-GoM. Including Mexico, the total basin contained an estimated 37.2-37.5Tg Corg. Regional US-GoM losses totaled 21.69Tg Corg. Corg losses differed significantly among anthropogenic impacts. Yet, seagrass restoration appears to be an important climate change mitigation strategy that could be implemented elsewhere throughout the tropics and subtropics.