scholarly journals Inorganic and black carbon hotspots constrain blue carbon mitigation services across tropical seagrass and temperate tidal marshes

2021 ◽  
Author(s):  
John Barry Gallagher ◽  
Vishnu Prahalad ◽  
John Aalders
Keyword(s):  
Salt Marsh ◽  
Organic Carbon ◽  
Salt Marshes ◽  
Inorganic Carbon ◽  
Blue Carbon ◽  
Tidal Marshes ◽  
Carbon Mitigation ◽  
Seagrass Meadows ◽  
First Time ◽  
Particulate Inorganic Carbon

Abstract Total organic carbon (TOC) sediment stocks as a CO2 mitigation service require exclusion of allochthonous black (BC) and particulate inorganic carbon corrected for water–atmospheric equilibrium (PICeq). For the first time, we address this bias for a temperate salt marsh and a coastal tropical seagrass in BC hotspots that represent two different blue carbon ecosystems of Malaysia and Australia. Seagrass TOC stocks were similar to the salt marshes with soil depths < 1 m (59.3 ± 11.3 and 74.9 ± 18.9 MgC ha− 1, CI 95% respectively). Both ecosystems showed larger BC constraints than their pristine counterparts did. However, the seagrass meadows’ mitigation services were largely constrained by both higher BC/TOC and PICeq/TOC fractions (38.0% ± 6.6% and 43.4% ± 5.9%, CI 95%) and salt marshes around a third (22% ± 10.2% and 6.0% ± 3.1% CI 95%). The results provide useful data from underrepresented regions, and, reiterates the need to consider both BC and PIC for more reliable blue carbon mitigation assessments.

scholarly journals Inorganic and black carbon hotspots constrain blue carbon mitigation services across tropical seagrass and temperate tidal marshes

2020 ◽  
Author(s):  
John Barry Gallagher ◽  
Vishnu Prahalad ◽  
John Aalders
Keyword(s):  
Salt Marsh ◽  
Organic Carbon ◽  
Salt Marshes ◽  
Inorganic Carbon ◽  
Blue Carbon ◽  
Tidal Marshes ◽  
Carbon Mitigation ◽  
Seagrass Meadows ◽  
First Time ◽  
Particulate Inorganic Carbon

AbstractTotal organic carbon (TOC) sediment stocks as a CO2 mitigation service requires exclusion of allochthonous black (BC) and particulate inorganic carbon corrected for water– atmospheric equilibrium (PICeq). For the first time, we address this bias for a temperate salt marsh and a coastal tropical seagrass in BC hotspots. Seagrass TOC stocks were similar to the salt marshes with soil depths < 1 m (59.3 ± 11.3 and 74.9 ± 18.9 MgC ha-1, CI 95% respectively) and sequestration rates of 1.134 MgC ha-1 yr-1. Both ecosystems showed larger BC constraints than their pristine counterparts. However, the seagrass meadows’ mitigation services were largely constrained by both higher BC/TOC and PICeq/TOC fractions (38.0% ± 6.6% and 43.4% ± 5.9%, CI 95%) and salt marshes around a third (22% ± 10.2% and 6.0% ± 3.1% CI 95%). The results demonstrate a need to account for both BC and PIC within blue carbon mitigation assessments.

scholarly journals Blue carbon stocks and exchanges along the California coast

2021 ◽  
Vol 18 (16) ◽  
pp. 4717-4732
Author(s):  
Melissa A. Ward ◽  
Tessa M. Hill ◽  
Chelsey Souza ◽  
Tessa Filipczyk ◽  
Aurora M. Ricart ◽  
...  
Keyword(s):  
Salt Marsh ◽  
Salt Marshes ◽  
Carbon Sources ◽  
Carbon Stocks ◽  
Blue Carbon ◽  
California Coast ◽  
Seagrass Meadows ◽  
Terrestrial Habitats ◽  
Isotope Mixing Models ◽  
Sediment Carbon

Abstract. Salt marshes and seagrass meadows can sequester and store high quantities of organic carbon (OC) in their sediments relative to other marine and terrestrial habitats. Assessing carbon stocks, carbon sources, and the transfer of carbon between habitats within coastal seascapes are each integral in identifying the role of blue carbon habitats in coastal carbon cycling. Here, we quantified carbon stocks, sources, and exchanges in seagrass meadows, salt marshes, and unvegetated sediments in six bays along the California coast. In the top 20 cm of sediment, the salt marshes contained approximately twice as much OC as seagrass meadows did, 4.92 ± 0.36 kg OC m−2 compared to 2.20 ± 0.24 kg OC m−2, respectively. Both salt marsh and seagrass sediment carbon stocks were higher than previous estimates from this region but lower than global and US-wide averages, respectively. Seagrass-derived carbon was deposited annually into adjacent marshes during fall seagrass senescence. However, isotope mixing models estimate that negligible amounts of this seagrass material were ultimately buried in underlying sediment. Rather, the vast majority of OC in sediment across sites was likely derived from planktonic/benthic diatoms and/or C3 salt marsh plants.

scholarly journals Blue Carbon Stocks and Exchanges Along the Pacific West Coast

2021 ◽  
Author(s):  
Melissa A. Ward ◽  
Tessa M. Hill ◽  
Chelsey Souza ◽  
Tessa Filipczyk ◽  
Aurora M. Ricart ◽  
...  
Keyword(s):  
Salt Marsh ◽  
Salt Marshes ◽  
Carbon Sources ◽  
Carbon Stocks ◽  
Blue Carbon ◽  
Seagrass Meadows ◽  
The Pacific ◽  
Terrestrial Habitats ◽  
Isotope Mixing Models ◽  
Sediment Carbon

Abstract. Salt marshes and seagrass meadows can sequester and store high quantities of organic carbon (OC) in their sediments relative to other marine and terrestrial habitats. Assessing carbon stocks, carbon sources, and the transfer of carbon between habitats within coastal seascapes are each integral in identifying the role of blue carbon habitats in coastal carbon cycling. Here, we quantified carbon stocks, sources, and exchanges in seagrass meadows, salt marshes, and unvegetated sediments in six bays along the Pacific coast of California. The salt marshes studied here contained approximately twice as much OC as did seagrass meadows, 23.51 ± 1.77 kg OC m−3 compared to 11.01 ± 1.18 kg OC m−3, respectively. Both seagrass and salt marsh sediment carbon stocks were higher than previous estimates from this region but lower than global and U.S.-wide averages, respectively. Seagrass-derived carbon was deposited annually into adjacent marshes during fall seagrass senescence. However, isotope mixing models estimate that negligible amounts of this seagrass material were ultimately buried in underlying sediment. Rather, the vast majority of OC in sediment across sites was likely derived from planktonic/benthic diatoms and C3 salt marsh plants.

scholarly journals Controls on soil organic carbon stocks in tidal marshes along an estuarine salinity gradient

2016 ◽  
Vol 13 (24) ◽  
pp. 6611-6624 ◽  
Author(s):  
Marijn Van de Broek ◽  
Stijn Temmerman ◽  
Roel Merckx ◽  
Gerard Govers
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Salt Marshes ◽  
Salinity Gradient ◽  
Tidal Marshes ◽  
Freshwater Marshes ◽  
Marsh Sediments ◽  
Maximum Turbidity Zone ◽  
Maximum Turbidity ◽  
Soc Stocks

Abstract. Tidal marshes are sedimentary environments and are among the most productive ecosystems on Earth. As a consequence they have the potential to reduce atmospheric greenhouse gas concentrations by sequestering organic carbon (OC). In the past decades, most research on soil organic carbon (SOC) storage in marsh environments has focused on salt marshes, leaving carbon dynamics in brackish and freshwater marshes largely understudied and neglecting the diversity among tidal marshes. We therefore conducted an extensive sampling campaign to quantify and characterize SOC stock in marshes along a salinity gradient in the Scheldt estuary (Belgium and the Netherlands). We find that SOC stocks vary significantly along the estuary, from 46 in freshwater marshes to 10 kg OC m−2 in salt marshes. Our data also show that most existing studies underestimate total SOC stocks due to shallow soil sampling, which also influences reported patterns in OC storage along estuaries. In all sampled tidal marsh sediments the SOC concentration is more or less constant from a certain depth downward. However, this concentration decreases with increasing salinity, indicating that the amount of stable SOC decreases from the upper estuary towards the coast. Although the net primary production of macrophytes differs along the estuary, our data suggest that the differences in OC storage are caused mainly by variations in suspended sediment concentration and stable particulate OC (POC) content in the water along the estuary. The fraction of terrestrial suspended sediments and POC that is transported downstream of the maximum turbidity zone is very limited, contributing to smaller amounts of long-term OC sequestration in brackish and salt marsh sediments. In addition, high rates of sediment deposition on freshwater tidal marshes in the maximum turbidity zone promote efficient burial of OC in these marsh sediments.

scholarly journals Blue carbon sequestration dynamics within tropical seagrass sediments: Long-term incubations for changes over climatic scales

2019 ◽  
Author(s):  
Chuan Chee Hoe ◽  
John Barry Gallagher ◽  
Chew Swee Theng ◽  
Norlaila Binti Mohd. Zanuri
Keyword(s):  
Carbon Sequestration ◽  
Organic Carbon ◽  
Loss Rate ◽  
Blue Carbon ◽  
Tight Coupling ◽  
Before And After ◽  
Reactivity Continuum ◽  
Particulate Inorganic Carbon

AbstractDetermination of blue carbon sequestration in seagrass sediments over climatic time scales relies on several assumptions, such as no loss of particulate organic carbon (POC) after one or two years, tight coupling between POC loss and CO2emissions, no dissolution of carbonates and removal of the stable black carbon (BC) contribution. We tested these assumptions via 500-day anoxic decomposition/mineralisation experiments to capture centennial parameter decay dynamics from two sediment horizons robustly dated as 2 and 18 years old. No loss of BC was detected, and decay of POC was best described for both horizons by near-identical reactivity continuum models. The models predicted average losses of 49% and 51% after 100 years of burial and 20–22 cm horizons, respectively. However, the loss rate of POC was far greater than the release rate of CO2, both before and after accounting for CO2from anoxic particulate inorganic carbon (PIC) production, possibly as siderite. The deficit could not be attributed to dissolved organic carbon or dark CO2fixation. Instead, evidence based on δ13CO2, acidity and lack of sulphate reduction suggested methanogenesis. The results indicate the importance of centennial losses of POC and PIC precipitation and possibly methanogenesis in estimating carbon sequestration rates.

scholarly journals Can mud (silt and clay) concentration be used to predict soil organic carbon content within seagrass ecosystems?

2016 ◽  
Author(s):  
O. Serrano ◽  
P. S. Lavery ◽  
C. M. Duarte ◽  
G. A. Kendrick ◽  
A. Calafat ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carbon Content ◽  
Clay Content ◽  
Cost Effective ◽  
Blue Carbon ◽  
Organic Carbon Content ◽  
Terrestrial Organic Matter ◽  
Seagrass Meadows ◽  
Clay Concentration ◽  
Seagrass Ecosystems

Abstract. The emerging field of blue carbon science is seeking cost-effective ways to estimate the organic carbon content of soils that are bound by coastal vegetated ecosystems. Organic carbon (Corg) content in terrestrial soils and marine sediments has been correlated with mud content (i.e. silt and clay), however, empirical tests of this theory are lacking for coastal vegetated ecosystems. Here, we compiled data (n = 1345) on the relationship between Corg and mud (i.e. silt and clay, particle sizes <63 μm) contents in seagrass ecosystems (79 cores) and adjacent bare sediments (21 cores) to address whether mud can be used to predict soil Corg content. We also combined these data with the δ13C signatures of the soil Corg to understand the sources of Corg stores. The results showed that mud is positively correlated with soil Corg content only when the contribution of seagrass-derived Corg to the sedimentary Corg pool is relatively low, such as in small and fast growing meadows of the genera Zostera, Halodule and Halophila, and in bare sediments adjacent to seagrass ecosystems. In large and long-living seagrass meadows of the genera Posidonia and Amphibolis there was a lack of, or poor relationship between mud and soil Corg content, related to a higher contribution of seagrass-derived Corg to the sedimentary Corg pool in these meadows. The relative high soil Corg contents with relatively low mud contents (i.e. mud-Corg saturation) together with significant allochthonous inputs of terrestrial organic matter could overall disrupt the correlation expected between soil Corg and mud contents. This study shows that mud (i.e. silt and clay content) is not a universal proxy for blue carbon content in seagrass ecosystems, and therefore should not be applied generally across all seagrass habitats. Mud content can only be used as a proxy to estimate soil Corg content for scaling up purposes when opportunistic and/or low biomass seagrass species (i.e. Zostera, Halodule and Halophila) are present (explaining 34 to 91% of variability), and in bare sediments (explaining 78% of the variability).

Changes in land use in the last two centuries in the Po lowlands (northern Italy)

2021 ◽  
Author(s):  
Matteo Meli ◽  
Luigi Bruno
Keyword(s):  
Land Use ◽  
Salt Marshes ◽  
Coastal Wetlands ◽  
Land Reclamation ◽  
Urban Expansion ◽  
Critical Role ◽  
Blue Carbon ◽  
Historical Maps ◽  
High Quality ◽  
Seagrass Meadows

&lt;p&gt;Changes in land use represent, after fossil-fuel combustion, the greatest cause of greenhouse-gases emission into the atmosphere. Coastal wetlands, also referred as coastal blue carbon ecosystems (e.g. salt marshes, mangrove forests, seagrass meadows, swamps), represent one of the most powerful C sinks among the Earth&amp;#8217;s ecosystems, being capable to sequester organic carbon (OC) at rates ca. 30-50 times higher than terrestrial forests. Historically, land reclamation for agriculture, farming and urban expansion, severely impacted coastal wetlands, causing their loss and degradation. Wetlands drainage lead to the oxidation of organic matter previously stored under anaerobic conditions and the release of CO&lt;sub&gt;2&lt;/sub&gt; into the atmosphere. Only recently the critical role of blue carbon ecosystems in climate-change mitigation has been recognised, highlighting the importance of protecting and studying these precious environments.&lt;/p&gt;&lt;p&gt;In this work, changes in land use in the last two centuries are reconstructed through comparison with historical maps. At the beginning of the 19&lt;sup&gt;th&lt;/sup&gt; century Napoleon Bonaparte requested the development of high-quality maps of occupied territories. Among these, the so-called &amp;#8216;Carta del Ferrarese&amp;#8217; (CdF), completed between 1812 and 1814, is composed of 38 sheets and represents, to a scale of 1:15.000, 240.000 hectares of the Po lowlands, roughly corresponding to the present-day Ferrara district. The CdF, archived at the Kriegsarchiv in Vienna, is an extraordinary example among historical maps for its high quality and accuracy, which constitute a two-centuries-old reliable paleo-landscape picture.&lt;/p&gt;&lt;p&gt;Within the Historical Land Use Change research project, leaded by the Emilia-Romagna Statistical and GIS Service, the CdF was scanned, accurately georeferenced and orthorectified, showing a surprising generalized match with recent maps. More than 31.000 polygons were digitized in a GIS environment and interpreted on the basis of the European Corine Land Cover codes, properly modified for the land uses at the time.&lt;/p&gt;&lt;p&gt;Comparison with the recent land use analysis, carried out in 2014, highlights changes in land use, mainly related to land reclamation. Salt marshes and swamps, originally extended for 100.000 hectares, were reduced of about 85%, starting from 1861. Major phases of land reclamation occurred in 1870s and 1960s. Geochemical analyses on shallow samples (depth &lt; 50 cm), depict OC content of artificially drained soils &lt; 5% of the total volume. Soil texture testifies to the almost complete mineralization of OC after reclamation. Only recently drained soils show higher OC content, in the range of 10-15%.&lt;/p&gt;

scholarly journals Major role of marine vegetation on the oceanic carbon cycle

2005 ◽  
Vol 2 (1) ◽  
pp. 1-8 ◽  
Author(s):  
C. M. Duarte ◽  
J. J. Middelburg ◽  
N. Caraco
Keyword(s):  
Organic Carbon ◽  
Salt Marshes ◽  
Total Carbon ◽  
Organic Carbon Content ◽  
Top Down ◽  
Coastal Habitats ◽  
Bottom Up ◽  
Seagrass Meadows ◽  
Carbon Burial ◽  
Oceanic Carbon

Abstract. The carbon burial in vegetated sediments, ignored in past assessments of carbon burial in the ocean, was evaluated using a bottom-up approach derived from upscaling a compilation of published individual estimates of carbon burial in vegetated habitats (seagrass meadows, salt marshes and mangrove forests) to the global level and a top-down approach derived from considerations of global sediment balance and a compilation of the organic carbon content of vegeatated sediments. Up-scaling of individual burial estimates values yielded a total carbon burial in vegetated habitats of 111 Tmol C y-1. The total burial in unvegetated sediments was estimated to be 126 Tg C y-1, resulting in a bottom-up estimate of total burial in the ocean of about 244 Tg C y-1, two-fold higher than estimates of oceanic carbon burial that presently enter global carbon budgets. The organic carbon concentrations in vegetated marine sediments exceeds by 2 to 10-fold those in shelf/deltaic sediments. Top-down recalculation of ocean sediment budgets to account for these, previously neglected, organic-rich sediments, yields a top-down carbon burial estimate of 216 Tg C y-1, with vegetated coastal habitats contributing about 50%. Even though vegetated carbon burial contributes about half of the total carbon burial in the ocean, burial represents a small fraction of the net production of these ecosystems, estimated at about 3388 Tg C y-1, suggesting that bulk of the benthic net ecosystem production must support excess respiration in other compartments, such as unvegetated sediments and the coastal pelagic compartment. The total excess organic carbon available to be exported to the ocean is estimated at between 1126 to 3534 Tg C y-1, the bulk of which must be respired in the open ocean. Widespread loss of vegetated coastal habitats must have reduced carbon burial in the ocean by about 30 Tg C y-1, identifying the destruction of these ecosystems as an important loss of CO2 sink capacity in the biosphere.

scholarly journals Can mud (silt and clay) concentration be used to predict soil organic carbon content within seagrass ecosystems?

2016 ◽  
Vol 13 (17) ◽  
pp. 4915-4926 ◽  
Author(s):  
Oscar Serrano ◽  
Paul S. Lavery ◽  
Carlos M. Duarte ◽  
Gary A. Kendrick ◽  
Antoni Calafat ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Carbon Content ◽  
Low Cost ◽  
Cost Effective ◽  
Scaling Up ◽  
Blue Carbon ◽  
Organic Carbon Content ◽  
Terrestrial Organic Matter ◽  
Seagrass Meadows ◽  
Seagrass Ecosystems

Abstract. The emerging field of blue carbon science is seeking cost-effective ways to estimate the organic carbon content of soils that are bound by coastal vegetated ecosystems. Organic carbon (Corg) content in terrestrial soils and marine sediments has been correlated with mud content (i.e., silt and clay, particle sizes < 63 µm), however, empirical tests of this theory are lacking for coastal vegetated ecosystems. Here, we compiled data (n =  1345) on the relationship between Corg and mud contents in seagrass ecosystems (79 cores) and adjacent bare sediments (21 cores) to address whether mud can be used to predict soil Corg content. We also combined these data with the δ13C signatures of the soil Corg to understand the sources of Corg stores. The results showed that mud is positively correlated with soil Corg content only when the contribution of seagrass-derived Corg to the sedimentary Corg pool is relatively low, such as in small and fast-growing meadows of the genera Zostera, Halodule and Halophila, and in bare sediments adjacent to seagrass ecosystems. In large and long-living seagrass meadows of the genera Posidonia and Amphibolis there was a lack of, or poor relationship between mud and soil Corg content, related to a higher contribution of seagrass-derived Corg to the sedimentary Corg pool in these meadows. The relatively high soil Corg contents with relatively low mud contents (e.g., mud-Corg saturation) in bare sediments and Zostera, Halodule and Halophila meadows was related to significant allochthonous inputs of terrestrial organic matter, while higher contribution of seagrass detritus in Amphibolis and Posidonia meadows disrupted the correlation expected between soil Corg and mud contents. This study shows that mud is not a universal proxy for blue carbon content in seagrass ecosystems, and therefore should not be applied generally across all seagrass habitats. Mud content can only be used as a proxy to estimate soil Corg content for scaling up purposes when opportunistic and/or low biomass seagrass species (i.e., Zostera, Halodule and Halophila) are present (explaining 34 to 91 % of variability), and in bare sediments (explaining 78 % of the variability). The results obtained could enable robust scaling up exercises at a low cost as part of blue carbon stock assessments.

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