•We assess the potential inclusion of blue carbon within Australia's Emissions Reduction Fund, emphasizing issues and approaches that have global relevance.•We identify twelve potential management ...actions then quantify and discuss the five most promising activities, encompassing the protection, restoration and creation of mangroves, tidal marshes and seagrasses.•On a per area basis, mean abatement intensity of organic carbon was highest for the management activity ‘(re)introduction of tidal flow’ which may result in mean annual abatement of 13 – 15 Mg Corg ha−1 yr−1 for mangrove and 6 – 8 Mg Corg ha−1 yr−1 for tidal marsh.•Our approach offers a template that uses best available information to identify options for carbon abatement through management of coastal landscapes.
There is increasing interest in protecting, restoring and creating ‘blue carbon’ ecosystems (BCE; mangroves, tidal marshes and seagrasses) to sequester atmospheric CO2-C and thereby contribute to climate change mitigation. While a growing number of countries aspire to report greenhouse gas emission and carbon sequestration changes from these ecosystems under voluntary international reporting requirements, few countries have domestic policy frameworks that specifically support the quantification and financing of carbon emission abatement through BCE management.
Australia, as home to approximately 5–11% of global blue carbon stocks, has a substantial interest in the development of blue carbon policy. Here we assess the potential inclusion of blue carbon within Australia's Emissions Reduction Fund, emphasizing issues and approaches that have global relevance. We used a participatory workshop of scientific experts and carbon industry stakeholders to identify blue carbon management actions that would meet the requirements of the Fund. In total, twelve actions were assessed for their greenhouse gas emission abatement potential and the ability to measure abatement reliably, using a combination of available data and qualitative and quantitative methods, including expert knowledge.
We identify and discuss the five most relevant and promising activities, encompassing the protection, restoration and creation of mangroves, tidal marshes and seagrasses. On a per area basis, mean abatement intensity of organic carbon (Corg) was highest for the (re)introduction of tidal flow resulting in establishment of mangrove (13–15 Mg Corg ha−1 yr−1) and tidal marsh (6–8 Mg Corg ha−1 yr−1), followed by land use planning for sea-level rise for the creation of new mangrove habitat (8 Mg Corg ha−1 yr−1). The avoided disturbance of existing mangroves, tidal marshes and seagrasses has the twofold benefit of avoiding remineralisation of existing stocks, plus the future annual abatement associated with the net sequestration of atmospheric CO2-C as Corg with the continued functioning of these BCE. Our approach offers a template that uses best available information to identify options for carbon abatement through management of coastal landscapes, and details current knowledge gaps and important technical aspects that need to be considered for implementation in carbon crediting schemes.
Coastal salt marshes are dynamic, intertidal ecosystems that are increasingly being recognised for their contributions to ecosystem services, including carbon (C) accumulation and storage. The ...survival of salt marshes and their capacity to store C under rising sea levels, however, is partially reliant upon sedimentation rates and influenced by a combination of physical and biological factors. In this study, we use several complementary methods to assess short-term (days) deposition and medium-term (months) accretion dynamics within a single marsh that contains three salt marsh vegetation types common throughout southeastern (SE) Australia.We found that surface accretion varies among vegetation assemblages, with medium-term (19 months) bulk accretion rates in the upper marsh rush (Juncus) assemblage (1.74 ± 0.13 mm yr−1) consistently in excess of estimated local sea-level rise (1.15 mm yr−1). Accretion rates were lower and less consistent in both the succulent (Sarcocornia, 0.78 ± 0.18 mm yr−1) and grass (Sporobolus, 0.88 ± 0.22 mm yr−1) assemblages located lower in the tidal frame. Short-term (6 days) experiments showed deposition within Juncus plots to be dominated by autochthonous organic inputs with C deposition rates ranging from 1.14 ± 0.41 mg C cm−2 d−1 (neap tidal period) to 2.37 ± 0.44 mg C cm−2 d−1 (spring tidal period), while minerogenic inputs and lower C deposition dominated Sarcocornia (0.10 ± 0.02 to 0.62 ± 0.08 mg C cm−2 d−1) and Sporobolus (0.17 ± 0.04 to 0.40 ± 0.07 mg C cm−2 d−1) assemblages.Elemental (C : N), isotopic (δ13C), mid-infrared (MIR) and 13C nuclear magnetic resonance (NMR) analyses revealed little difference in either the source or character of materials being deposited among neap versus spring tidal periods. Instead, these analyses point to substantial redistribution of materials within the Sarcocornia and Sporobolus assemblages, compared to high retention and preservation of organic inputs in the Juncus assemblage. By combining medium-term accretion quantification with short-term deposition measurements and chemical analyses, we have gained novel insights into above-ground biophysical processes that may explain previously observed regional differences in surface dynamics among key salt marsh vegetation assemblages. Our results suggest that Sarcocornia and Sporobolus assemblages may be particularly susceptible to changes in sea level, though quantification of below-ground processes (e.g. root production, compaction) is needed to confirm this.
In this study, we examined changes in isotopic (¹³C and ¹⁴C) and spectroscopic (UV and ¹³C NMR) properties of dissolved organic carbon (DOC) in relation to soil organic matter (SOM) to elucidate the ...sources and sinks of DOC as water percolates through the soils of two contrasting upland coastal California ecosystems--a redwood forest and a coastal prairie. Despite differences in the distribution of C stocks and litter chemistry at these two sites, we found similar shifts in DOC chemistry with soil depth. DOC concentrations dropped rapidly with increasing depth, with an accompanying decrease in the C:N ratio, an increase in the δ¹³C value and an decrease in specific UV adsorption. In the grassland soil, Δ¹⁴C values declined from current atmospheric values (+70per thousand) in the surface horizon to -75per thousand at 100 cm. In the redwood soil, the Δ¹⁴C value of 111per thousand in O horizon leachates was indicative of OM with a residence time of 8-10 yrs, with a decrease in Δ¹⁴C values to -80per thousand at 100 cm. Solid-state CP/MAS ¹³C NMR spectra were generally most similar to highly humified OM, with a general decrease in the relative abundance of aromatic compounds and an increase in the alkyl C/O-alkyl C ratio with increasing depth. All of these trends are consistent with the shifts in SOM properties with increasing depth, which are interpreted to mean a shift from fresh plant material to older, highly altered OM. In this Mediterranean climate, we found distinct seasonal shifts in the quantity and composition of DOC found in soil solution during the winter rainy period that was also consistent with a shift from recent labile substrates to older, highly altered OM. These results fit in with a growing body of literature suggesting that the source of much of the DOC within mineral soils is the local soil OM, and the ¹⁴C data, in particular, indicate that DOC at depth is not simply the fraction of surficial leachates that have not been adsorbed or decomposed. Rather, exchange reactions with a portion of the more stabilized SOM pool exert the strongest control on both the concentration and composition of DOC found in these soils.
As nations debate whether and how best to include the agricultural sector in greenhouse gas pollution reduction schemes, the role of soil organic carbon as a potential large carbon sink has been ...thrust onto center stage. Results from most agricultural field trials indicate a relative increase in soil carbon stocks with the adoption of various improved management practices. However, the few available studies with time series data suggest that this relative gain is often due to a reduction or cessation of soil carbon losses rather than an actual increase in stocks. On the basis of this observation, we argue here that stock change data from agricultural field trials may have limited predictive power when the state of the soil carbon system is unknown and that current IPCC (Intergovernmental Panel on Climate Change) accounting methodologies developed from the trial results may not properly credit these management activities. In particular, the use of response ratios is inconsistent with the current scientific understanding of carbon cycling in soils and response ratios will overestimate the net–net sequestration of soil carbon if the baseline is not at steady state.
Spectroscopy is a powerful means of increasing the availability of soil data necessary for understanding carbon cycling in a changing world. Here, we develop a calibration transfer methodology to ...appropriately apply an existing mid infrared (MIR) spectral library with analyte data on the distribution of soil organic carbon (SOC) into particulate (POC), mineral-associated (MAOC), and pyrogenic (PyC) forms to nearly 8000 soil samples collected in the Great Plains ecoregion of the United States. We then use this SOC fraction database in combination with a machine learning-based predictive soil mapping approach to explore the controls on the distribution of fractions through soil profiles and across the region. The relative abundance of each fraction had unique depth distribution profiles with POC fraction dropping exponentially with depth, the MAOC fraction having a broad distribution with a maxima at 35–50 cm, and the PyC fraction showed a slight subsurface maxima (10–20 cm) and then a steady decline with increasing depth. Within the Great Plains ecoregion, clay content was a strong control on the total amount and relative proportion of each fraction in both the surface and subsoil horizons. Sandy soils and soils in cool semi-arid regions contained significantly more POC relative to the MAOC and PyC fractions. Cultivated soils had significantly less SOC than grassland soils with losses following a predictable pattern: POC > MAOC ≫ PyC. This SOC fraction database and resulting maps can now form the basis for improved representation of SOC dynamics in biogeochemical models.
Previous studies have shown that residue chemistry and microbial community structure change during decomposition, however little is known about the relationship between C-chemistry and microbial ...community structure. To address this knowledge gap, we studied C-chemistry and microbial community structure during the decomposition of eucalypt, wheat and vetch residues with and without additional inorganic N. Bags containing ground residues of eucalypt, wheat, and vetch were buried in sand microcosms after inoculation with a diverse microbial community. Respiration was measured over an incubation period of 150 days. At different times during incubation, total C and N of the residues were analysed and residue carbon chemistry was determined by
13C-NMR (nuclear magnetic resonance) spectroscopy. Microbial communities were assessed by phospholipid fatty acid (PLFA) analyses.
Results indicated that during decomposition, residue C-chemistry and microbial community composition changed over time and differed between residue types. Changes in microbial community structure were associated with changes in residue C-chemistry, mainly the relative content of aryl-C and O-alkyl-C. Addition of N increased cumulative respiration, altered C-chemistry during decomposition, particularly in high C/N residues (wheat and eucalypt), and changed microbial succession leading to an earlier establishment of a stable microbial community structure. N addition to eucalypt and wheat reduced the decomposition of aryl-C compounds.
Excessive accumulation of plant ‘wrack’ on beaches as a result of coastal development and beach modification (e.g. groin installation) is a global problem. This study investigated the potential for ...converting beach-cast seagrass wrack into biochar as a ‘climate-friendly’ disposal option for resource managers. Wrack samples from 11 seagrass species around Australia were initially screened for their biochar potential using pyrolysis techniques, and then two species – Posidonia australis and Zostera muelleri – underwent detailed analyses. Both species had high levels of refractory materials and high conversion efficiency (48–57%) of plant carbon into biochar carbon, which is comparable to high-quality terrestrial biochar products. P. australis wrack gave higher biochar yields than Z. muelleri consistent with its higher initial carbon content. According to 13C NMR, wrack predominantly comprised carbohydrates, protein, and lignin. Aryl carbon typical of pyrogenic materials dominated the spectrum of the thermally-altered organic materials. Overall, this study provides the first data on the feasibility of generating biochar from seagrass wrack, showing that biocharring offers a promising climate-friendly alternative to disposal of beach wrack in landfill by avoiding a portion of the greenhouse gas emissions that would otherwise occur if wrack was left to decompose.
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•Accumulation of seagrass wrack on beaches has become a global disposal challenge.•We explore the feasibility of converting seagrass wrack into biochar via pyrolysis.•Biocharring offsets CO2 emissions and creates a commercially-valuable byproduct.•Wrack carbon was converted into biochar with an efficiency of 48–57%.
Nitrogen (N) loss from intensive animal husbandry leads to economic loss and environmental damage. Lignite has a demonstrated capacity to suppress ammonia (NH
3
) volatilisation from manure and this ...has been attributed to the pH, cation exchange capacity (CEC), pH buffer capacity and labile carbon (C) content of the lignite. Whilst lignite is effective in mitigating NH
3
loss, the capacity for N retention and how this is influenced by the lignite's properties are not well studied. It is unclear if lignites from different mines will have comparable N retention under similar conditions. In this study, we characterised five Victorian lignites for their C-containing functional groups, surface morphology and chemical properties. These were then related to the ammonium (
) adsorption capacity of the lignites using a batch isotherm technique. The contribution of biological immobilisation to the N retention capacity of the lignites was determined using
15
N tracing in an incubation study. All lignites were acidic (pH
H2O
: 3.3-5.8; pH
CaCl2
: 3.0-5.4). The lignite had similar patterns of distribution of C functional groups with the carboxyl C between 2.8% and 5.3%. The maximum
adsorption capacity (Q
max
) varied with the composition of the lignite and correlated positively with the lignites' CEC, pH and carboxyl groups. Increase in pH, especially from pH >5, resulted in up to 3-fold increase in Q
max
(25.6 mg g
−1
), likely due to deprotonation of carboxyl groups. Compared to
adsorption, the biological immobilisation of
did not play a substantial role in the overall lignite's N retention capacity.
Highlights
Victorian lignites were assessed for their
retention capacity using adsorption isotherms and
15
N tracing.
adsorption capacity of lignites increased (up to 3-fold) with pH, especially from pH 5 to 7.
Biological immobilisation did not play a substantial role in the
retention capacity of the lignites.
pH-dependent
adsorption was the dominant means by which lignite retained
.
To understand the hydrologic and biogeochemical controls on the age and recalcitrance of dissolved organic matter (DOM) found in stream waters, we combined hydrometric monitoring along a topographic ...gradient from ridge to channel with isotopic (13C and 14C) and spectroscopic (UV and 13C nuclear magnetic resonance) analyses of soil and stream water samples in a small coastal watershed in California. With increasing discharge, dissolved organic carbon concentrations increased from 2.2 to 10.9 mg C L-1, delta 14C values increased from -125 to +120 per thousand, delta 13C values decreased from -24 to -29 per thousand, C:N ratios increased from 6.5 to 15.4, and specific UV adsorption increased from 1.4 to 3.8 L mg C-1 m-1. These changes in DOM composition are consistent with a shift in source from old and recalcitrant soil organic matter (OM) sources found in deep soil horizons to young and relatively fresh OM sources found in the surface horizons. Results from this study suggest upland soils of the watershed become DOM production limited as indicated by a seasonal depletion and chemical shift in soil DOM, whereas highly productive soils in the hollow act as a near-infinite DOM source. Hydrologic connectivity of this DOM-rich riparian source region to the stream ultimately constrains DOM export, and the stream DOM composition reflects the combined influence of soil biogeochemical cycling of OM and hydrologic routing of water through the landscape.
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