Net Carbon Sink Research Articles

What can the Glasgow Declaration on Forests bring to global emission reduction?

What can the Glasgow Declaration on Forests bring to global emission reduction?

A network-based framework for characterizing urban carbon metabolism associated with land use changes: A case of Beijing city, China

Land use and cover changes associated with urbanization is an important source of the global carbon emissions. Understanding of the driving mechanism of the LUCC-related carbon emissions is of great significance to enhance the benefit of reducing anthropogenic emissions, estimate land use-carbon flow feedbacks, and formulate climate policies. In the present study, we established a network-based framework integrated with ecological network analysis (ENA) and patch-generating land use simulation (PLUS) models to quantify the LUCC impacts on carbon flow variabilities during 1990–2018, using Beijing, China as a target case. Results showed that the total carbon emissions increased from 1990 (10.69 Mt C yr−1) to 2010 (20.61 Mt C yr−1), followed with steady decease to 2018 (18.63 Mt C yr−1), which predominated over total carbon sequestrations with a factor of 28.5 times in 1990 to 48.5 times in 2018. Both the net carbon source and carbon sink associated with land use changes showed decreasing trends over time, with decreasing rates at 5.5% and 4.6%, respectively. Most of this decrease in net carbon source was attributed to emission intensity decline of transportation and industrial land. The decrease of net carbon sink was attributed to slower urban land shrinkage rate and recover of green space. The simulated decarbonization paths suggests there is still a great potential for carbon emission reduction in the city. Carbon emission reduction of different scenario ranged from 19% to 44%, among which 96.1%–97.5% was contributed by decline of emission intensities and 2.4%–3.9% was resulted from recovery of carbon sink land. Moreover, the additional land use adjustment caused extra 6.1%–9.4% carbon emission reduction and 2.2%–5.2% carbon sequestration growth comparing the situation in 2018, which mainly attributed to carbon emission intensities decline and reforest. Overall, our results provide insights into the key carbon flow paths that are necessary for making land use policy towards a more sustainable urban metabolism.

Spatio-temporal evolution and influencing factors of net carbon sink in marine aquaculture in China

Marine aquaculture not only has considerable economic benefits, but also provides high-quality “decarbonization space” for carbon neutrality, which is of great significance for realizing the goal of “double carbon”. Using the two-stage LMDI (logarithmic mean division index) method, this paper comprehensively analyzes the mechanism of net carbon sink capacity of mariculture in China from five factors: aquaculture structure, aquaculture efficiency, aquaculture scale, competitiveness of shellfish and algae and aquaculture mode. The results show that: 1) the net carbon sink of mariculture in China has increased year by year from 2010 to 2019, with obvious heterogeneous spatial distribution characteristics in three marine economic zone. 2) The improvement of aquaculture efficiency and innovation of aquaculture model contribute the most to the increase of carbon sink, and technological progress plays an increasingly important role. 3) The weak competitiveness of shellfish and algae seriously hinders the growth rate of carbon sink, and is the main reason for the increasing tightening of carbon sink space. 4) Regional heterogeneity analysis shows that the mechanism of increasing carbon sink in marine aquaculture is regionally heterogeneous and resource-dependent. Based on these findings, strategies are proposed to emphasize the ecological values of marine aquaculture, accelerate the technological innovation of deep-sea marine aquaculture, improve the organizational system and the management level, and expand the space for marine carbon sink.

Process-oriented analysis of dominant sources of uncertainty in the land carbon sink

The observed global net land carbon sink is captured by current land models. All models agree that atmospheric CO2 and nitrogen deposition driven gains in carbon stocks are partially offset by climate and land-use and land-cover change (LULCC) losses. However, there is a lack of consensus in the partitioning of the sink between vegetation and soil, where models do not even agree on the direction of change in carbon stocks over the past 60 years. This uncertainty is driven by plant productivity, allocation, and turnover response to atmospheric CO2 (and to a smaller extent to LULCC), and the response of soil to LULCC (and to a lesser extent climate). Overall, differences in turnover explain ~70% of model spread in both vegetation and soil carbon changes. Further analysis of internal plant and soil (individual pools) cycling is needed to reduce uncertainty in the controlling processes behind the global land carbon sink.

Inventory of China’s Net Biome Productivity since the 21st Century

Net biome productivity (NBP), which takes into account abiotic respiration and metabolic processes such as fire, pests, and harvesting of agricultural and forestry products, may be more scientific than net ecosystem productivity (NEP) in measuring ecosystem carbon sink levels. As one of the largest countries in global carbon emissions, in China, however, the spatial pattern and evolution of its NBP are still unclear. To this end, we estimated the magnitude of NBP in 31 Chinese provinces (except Hong Kong, Macau, and Taiwan) from 2000 to 2018, and clarified its temporal and spatial evolution. The results show that: (1) the total amount of NBP in China was about 0.21 Pg C/yr1. Among them, Yunnan Province had the highest NBP (0.09 Pg C/yr1), accounting for about 43% of China’s total. (2) NBP increased from a rate of 0.19 Tg C/yr1 during the study period. (3) At present, NBP in China’s terrestrial ecosystems is mainly distributed in southwest and south China, while northwest and central China are weak carbon sinks or carbon sources. (4) The relative contribution rates of carbon emission fluxes due to emissions from anthropogenic disturbances (harvest of agricultural and forestry products) and natural disturbances (fires, pests, etc.) were 70% and 9.87%, respectively. This study emphasizes the importance of using NBP to re-estimate the net carbon sink of China’s terrestrial ecosystem, which is beneficial to providing data support for the realization of China’s carbon neutrality goal and global carbon cycle research.

Hemiboreal forests’ CO2 fluxes response to the European 2018 heatwave

In summer 2018, Europe experienced a heatwave that impacted the forest carbon cycle. We assessed the influence of elevated temperatures on the carbon exchange of three forest stands of different types (coniferous, deciduous, and conifer-broadleaved) and a clear-cut area located in the geographical vicinity within a hemiboreal zone. The carbon fluxes were calculated using the eddy-covariance technique. Over the period of anomaly high temperatures, the NEE of a deciduous (alder) forest was similar to the previous year due to the reduction of both GPP and ER of the same magnitude. Warm days in spring and autumn allowed for the GPP offset, and the total NEE of vegetation season 2018 was more negative than of 2017. Coniferous (pine and spruce) forest carbon uptake decreased during the temperature anomaly as a result of GPP reduction being higher than the decrease in ER. Spring warming had almost no effect on the carbon exchange, while ER and GPP increased in autumn warm days. As a result, annual ER was higher in 2018 than in 2017, and the NEE was smaller. The coniferous forest was most resistant to the heatwave, most probably because of its adaption to low soil water content. Contrary to our expectations, a mixed conifer-broadleaved forest (pine, spruce, birch, clear-cuts) was more affected by the heatwave than a pine-dominated forest. It switched from net carbon sink during the vegetation season of 2017 to net carbon source in 2018. Almost three times higher amount of carbon was released in 2018 as a result of GPP reduction. The clear-cut area carbon exchange was the most vulnerable to the heatwave influence out of all study sites. A more prominent reduction of GPP resulted in smaller NEE. Warm days in spring and autumn did not offset the temperature anomaly impact, as was observed for the forested ecosystems.

Can Agricultural Productive Services Promote Agricultural Environmental Efficiency in China?

Agricultural productive services are important paths to realize the development of green agriculture, while the effect of agricultural productive services on the agricultural environment and its influencing mechanism are not yet clear. With the panel data of agricultural production in China from 2004 to 2019, by using multi-output stochastic frontier analysis with an output-oriented distance function, this study investigates agricultural environmental efficiency based on net carbon sinks. Then, this study explores the effect of agricultural productive services on agricultural environmental efficiency and its mechanisms by adopting ordinary least squares regression with fixed-effect panel model, causal steps approach, and spatial econometric method. The main findings are as follows: Firstly, agricultural productive services enhance agricultural productivity and agricultural environment by optimizing inputs and increasing outputs, and thus improve agricultural environmental efficiency. This result holds steadily after using instrumental variables to deal with endogeneity, changing the measurement of the dependent and independent variables, and subdividing the sample. Secondly, the pathways of agricultural productive services affecting agricultural environmental efficiency are mainly reflected in technology progress, planting structure adjustment, factor allocation optimization, and spatial spillover. Thirdly, due to the law of diminishing marginal returns, the impact of agricultural productive services on agricultural environmental efficiency is more significant when the level of agricultural productive services is relatively low. To improve agricultural environmental efficiency, we suggest implementing different productive service strategies in different regions, strengthening information integration, and improving infrastructure.

Manila clam and Mediterranean mussel aquaculture is sustainable and a net carbon sink

Aquaculture is a globally expanding industry that contributes to feeding an increasing global population. Shellfish cultivation is one of the largest sectors of aquaculture and one of the few food productions that have the potential capacity of acting as carbon sink. In fact, >90 % of bivalve shells are calcium carbonate (CaCO3), synthetized during biocalcification process, which incorporates a molecule of CO2. Manila clam (Venerupis philippinarum, Adams & Reeves, 1850) and Mediterranean mussel (Mytilus galloprovincialis, Lamarck, 1819) are two of the major groups of cultivated shellfish. Our aim was to assess the potential role of those two bivalve species in the overall marine carbon balance using an ecosystem approach, and to evaluate if they can be definitely regarded as carbon sink. The contribution to CO2 emissions (as CO2 eq./kg of fresh products) due to mollusk farming has been also calculated as carbon-source term by means of Life Cycle Assessment (LCA). LCA is nowadays the most shared and accepted tool for evaluating the environmental impacts of aquaculture productions. As a case study, the Sacca di Goro coastal lagoon (Northern Adriatic Sea, Italy) has been considered, because it is the premier site in Europe for clam farming, and one of the most important for mussels. Our study has shown that for each kilogram of harvested and packaged clams and mussels, shell formation throughout the mollusk growth allows to permanently capture 254 and 146 g of CO2, in the face of 22 and 55 g CO2 eq. emitted for farming, respectively. As a result, clams and mussel aquaculture could be considered as a carbon sink, with a net carbon capture capacity of 233 and 91 g CO2/kg of fresh product, respectively. In a wider context, bivalve aquaculture could be included in the carbon trading system and played a role towards the carbon-neutral economy.

The evolution of dissolved inorganic carbon (DIC) and δ13CDIC in acid mine drainage polluted karst rivers: Preliminary findings from laboratory experiments

Acid mine drainage (AMD) has caused serious pollution in the surface water environments of karst areas, but the effect of AMD on the dissolved inorganic carbon (DIC) dynamics in the receiving karst rivers remains poorly understood. The AMD and karst river water were sampled from the Yangliujie River watershed in Southwest China, and mixed different proportions of AMD and karst river water in a laboratory experiment to simulate seasonal hydrological conditions in the river, in an attempt to explore the impact of AMD on the loss rate and evolution of DIC in karst river water. The results showed that AMD can cause a rapid pH drop in karst river water, resulting in approximately 41.0 ± 11.8 % DIC loss in the early stage of mixing as CO2(g) release to the atmosphere. With the biological or chemical oxidation of Fe2+, and followed by Fe3+ biogenic formation of schwertmannite or hydrolysis, the pH decreased and the DIC concentration further decreased in the mixed samples, the degree of decrease was related to the oxidation rate of Fe2+. With decreasing DIC concentration, δ13CDIC enrichment gradually increased. When the mixing ratio of AMD was large, the total H+ in AMD and H+ generated by the oxidation of Fe2+ exceeded the HCO3− content in karst river water, the isotopic enrichment coefficient caused by the initial mixing and the end of the reaction was small, and the DIC transformation was mainly dominated by the loss of CO2(g). When a small proportion of AMD was mixed in, the HCO3− concentration in the mixed water sample was in excess of the H+ produced by Fe2+ and the total H+ in AMD, the isotopic enrichment coefficient caused by the initial mixing and the end of the reaction was larger, and the DIC conversion was mainly affected by HCO3− dehydration. These preliminary findings support evidence showing DIC conversion and loss in AMD-affected karst rivers increase the transfer of carbon dioxide to the atmosphere, which diminishes net carbon sink fluxes in karst river basins, so reasonable AMD treatment methods should be applied to minimize these negative impacts.

The European forest carbon budget under future climate conditions and current management practices

Abstract. To become carbon neutral by 2050, the European Union (EU27) net carbon sink from forests should increase from the current level of about −360 to −450 Mt CO2eq yr−1 by 2050. Reaching this target requires additional efforts, which should be informed by the expected interactions between current age-class distributions, the effect of forest management practices and the expected impacts of future climate change. However, modelling the combined effect of these drivers is challenging, since it requires a mechanistic assessment of climate impacts on primary productivity and heterotrophic respiration and a detailed representation of the forest age structure and of the management practices across the entire EU. To achieve this goal, we combined the output provided by four land–climate models – run under two different Representative Concentration Pathway scenarios (RCP2.6 and RCP6.0) – to parameterize the input data used in an empirical forest growth model. This hybrid modelling approach aims to quantify the impact of climate change and forest management on the long-term (i.e. to 2100) evolution of the EU27 + UK forest carbon budget. This approach was tested using a business-as-usual (BAU) scenario, based on the continuation of the management practices applied by EU member states within the historical period 2000–2015. We emphasize that our study does not explore a specific policy scenario but describes a methodological framework. Our results highlight that, under our BAU case, the EU27 + UK forest C sink would decrease to about −250 Mt CO2eq yr−1 in 2050 and −80 Mt CO2eq yr−1 by 2100. The main driver of the long-term evolution of the forest C sink is the ongoing ageing process of the European forests, mostly determined by past and ongoing management. In addition, climate change may further amplify or mitigate this trend. Due to the large uncertainty in climate projections, in 2050 the net C sink may range from −100 to −400 Mt CO2eq yr−1 under RCP2.6 and from −100 to −300 Mt CO2eq yr−1 under RCP6.0. These results suggest that while a change in management practices would be needed to reverse an otherwise declining trend in the sink, climate change adds a considerable uncertainty, potentially nearly doubling or halving the sink associated with management.

Spatiotemporal dynamics of forest ecosystem carbon budget in Guizhou: customisation and application of the CBM-CFS3 model for China

BackgroundCountries seeking to mitigate climate change through forests require suitable modelling approaches to predict carbon (C) budget dynamics in forests and their responses to disturbance and management. The Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3) is a feasible and comprehensive tool for simulating forest C stock dynamics across broad levels, but discrepancies remain to be addressed in China. Taking Guizhou as the case study, we customised the CBM-CFS3 model according to China’s context, including the modification of aboveground biomass C stock algorithm, addition of C budget accounting for bamboo forests, economic forests, and shrub forests, improvement of non-forest land belowground slow dead organic matter (DOM) pool initialisation, and other model settings.ResultsThe adequate linear relationship between the estimated and measured C densities (R2 = 0.967, P < 0.0001, slope = 0.904) in the model validation demonstrated the high accuracy and reliability of our customised model. We further simulated the spatiotemporal dynamics of forest C stocks and disturbance impacts in Guizhou for the period 1990–2016 using our customised model. Results shows that the total ecosystem C stock and C density, and C stocks in biomass, litter, dead wood, and soil in Guizhou increased continuously and significantly, while the soil C density decreased over the whole period, which could be attributed to deforestation history and climate change. The total ecosystem C stock increased from 1220 Tg C in 1990 to 1684 Tg C in 2016 at a rate of 18 Tg C yr−1, with significant enhancement in most areas, especially in the south and northwest. The total decrease in ecosystem C stock and C expenditure caused by disturbances reached 97.6 Tg C and 120.9 Tg C, respectively, but both represented significant decreasing trends owing to the decline of disturbed forest area during 1990–2016. Regeneration logging, deforestation for agriculture, and harvest logging caused the largest C stock decrease and C expenditure, while afforestation and natural expansion of forest contributed the largest increases in C stock.ConclusionsThe forests in Guizhou were a net carbon sink under large-scale afforestation throughout the study period; Our customised CBM-CFS3 model can serve as a more effective and accurate method for estimating forest C stock and disturbance impacts in China and further enlightens model customisation to other areas.

Simultaneous Measurements of Dissolved Organic Carbon and Soil Respiration Reveal Reduced Soil Carbon Loss Under Nitrogen Addition in a Montane Forest

AbstractA major uncertainty in the estimation of soils acting as net carbon (C) sinks or sources stem from the effects of anthropogenic nitrogen (N) input on the balance between plant C input and soil C loss. In contrast to the generally observed increasing pattern of plant C input, the response of soil C loss to increased N deposition remains elusive, largely due to its large temporal variation. Here simultaneous measurements of two major soil C loss pathways, including dissolved organic carbon (DOC) leaching and soil respiration, were conducted for 5 and 3 yr, respectively, to assess the effects of N addition on soil C loss in an N‐limited montane forest. The effects were seasonal, depth and N level dependent and the two pathways responded asynchronously to N addition. Significant decreases in DOC concentrations and fluxes in leachates from the organic layer were observed during autumn/winter under a high N addition rate (40 kg N/ha/yr). No significant impact of N addition on DOC concentrations or fluxes was observed for leachates from the mineral soil horizon. Biodegradability was low for DOC from both soil layers and was not consistently influenced by N addition. Soil respiration was significantly decreased under high N addition. Annual soil C loss (estimated by summing DOC leaching from the mineral horizon and soil respiration) showed that N addition reduced soil C loss consistently over years, implying that the forest soil is likely a C sink under excess N deposition, which should be confirmed with longer term monitoring.

Seasonal carryover of water and effects on carbon dynamics in a dryland ecosystem

AbstractNet primary productivity in arid and semiarid regions is controlled by water availability for which rainfall has been a commonly used proxy at annual scales. However, the hydrological partitioning occurring through the water balance can also shape both seasonal and annual net ecosystem productivity. In this study, we used 10 years of water and carbon flux measurements in a mixed shrubland watershed of the Chihuahuan Desert to investigate the seasonal variability and controls on net ecosystem production. Over this period, the site exhibited a bimodal rainfall regime with an average of 211 and 67 mm for the wet (July–December) and dry (January–June) periods of the year, respectively. During the wet season, soil infiltration and channel transmission losses led to an average of 35.8 mm of water stored in the subsurface for subsequent dry periods. By contrast, dry seasons consumed 30.3 mm of stored subsurface water to fulfill the ecosystem water demand, particularly during the springtime. In response, gross primary productivity occurred in equal amounts for both seasons, while ecosystem respiration was substantially higher during the wet season. This resulted in the mixed shrubland acting as an annual net sink of carbon (average of 153.2 g C m−2 year−1) of which 65% occurred during the dry season. We determined that the wet season provided water in excess of vegetation demands in that season, a portion of which was stored in the watershed subsurface for subsequent use, leading to a legacy effect. Gross primary productivity during the dry season was dependent on carryover soil moisture accessed by deep‐rooted shrubs. Our coordinated observations of water–carbon dynamics revealed that water availability during the wet season can sustain the annual ecosystem productivity by impacting the subsequent dry season carbon uptake.

From sink to source: changing climate and disturbance regimes could tip the 21st century carbon balance of an unmanaged mountain forest landscape

Abstract Forests are one of the most important components of the global carbon cycle. Consequently, forest protection as a nature-based climate solution has garnered increasing interest. Protected areas instated to safeguard biodiversity provide an opportunity to maximize carbon storage in situ, with important co-benefits between conservation and climate change mitigation. However, changing climate and disturbance regimes put this carbon storage function at risk. Here we investigated carbon sequestration and storage in a protected landscape in the German Alps (Berchtesgaden National Park) throughout the 21st century. We simulated the impacts of climate change as well as increasing wind and bark beetle disturbances on cumulative Net Ecosystem Production using a process-based forest landscape model. Considering a wide range of potential changes in wind frequency and speed under a variety of climate change scenarios, we addressed the question under which future conditions the landscape will turn from a carbon sink to a carbon source. While the landscape was a net carbon sink at the end of the simulation in 76 per cent of the simulation runs, increasing disturbances and climate change greatly reduced its carbon sink capacity. Under RCP2.6, the landscape remained a robust carbon sink even under elevated disturbance (probability of turning from sink to source between 0 per cent and 25 per cent). In contrast, carbon release was likely under RCP8.5 even with little change in the disturbance regime (probability: 30 per cent to 95 per cent). Productive areas in lower elevations that currently have the highest carbon density on the landscape were contributing most strongly to a reduction of the carbon sink strength. Our study reveals that the effect of protected areas acting as nature-based climate solutions might be overestimated if the risks from changing climate and disturbance regimes are neglected. We therefore call for a more explicit consideration of future forest dynamics in the discussion of the potential role of forests in climate change mitigation.

Sea level rise drives carbon and habitat loss in the U.S. mid-Atlantic coastal zone

Coastal marshes and seagrass beds store millions of tons of carbon in their sediments and sequester carbon at higher per-area rates than most terrestrial ecosystems. There is substantial interest in this “blue carbon” as a carbon mitigation strategy, despite the major threat that sea level rise (SLR) poses to these habitats. Many projections of habitat and carbon change with SLR emphasize the potential for inland marsh migration and increased rates of marsh carbon sequestration, but do not consider carbon fluxes associated with habitat conversion. We integrated existing data and models to develop a spatial model for predicting habitat and carbon changes due to SLR in six mid-Atlantic U.S. states likely to face coastal habitat loss over the next century due to low tidal ranges and sediment supply. Our primary model projection, using an intermediate SLR scenario (1.2 m SLR by 2104), predicts loss of 83% of existing coastal marshes and 26% of existing seagrasses in the study area. In addition, 270,000 hectares of forest and forested wetlands in low-lying coastal areas will convert to coastal marshes. These SLR-driven habitat changes cause the study area to shift from a carbon sink to a source in our primary model projection. Given the many uncertainties about the habitat and carbon changes represented in our model, we also identified the parameters and assumptions that most strongly affected the model results to inform future research needs. These included: land availability for inland marsh migration, the baseline extent and location of coastal marshes, proportion of stored carbon emitted from lost habitats (coastal marsh sediments or terrestrial biomass carbon), and methane emissions from freshwater habitats. The study area switched from a net carbon sink to a net carbon source under SLR for all but three model runs; in those runs, net carbon sequestration declined by 57–99%.

Research on the Impact of Rural Population Structure Changes on the Net Carbon Sink of Agricultural Production-Take Huan County in the Loess Hilly Region of China as an Example

People are the fundamental purpose and driving force of agricultural development. The changes in population structure can directly affect social and economic development of rural areas and the entire process of agricultural production. This paper takes Huan County in the Loess Hilly Region of China as the evaluation object, the townships as the evaluation unit, the change of rural population structure as the key point, and the agricultural production as the mediating factor, to study the mechanism of agricultural net carbon sinks. The results show: 1) From 2009 to 2018, the number of rural labor force in Huan County was seriously lost, the quality of the labor force was steadily improved, and the age of the labor force was increased. The number of agricultural employees dropped from 72.6 to 49.4%. The number of people with high school education or above increased from 9.7 to 15.1%. Those over working age who participated in the labor force rose from 5.2 to 8.3%. 2) The Loess Hilly Region in the northwest of Huan County was “grain-trending,” and the River Valley and Plain Area in the southeast was “grain-removing.” The input structure index both increased first and then decreased. and the Loess Hilly Region was more dependent on the fertilizer. 3) The rural population structure affects the agricultural net carbon sink by affecting the planting structure index and the input structure index. The rural population quantity and quality structure have a significant positive effect on the agricultural net carbon sink, while the population age structure has a significant negative effect on the agricultural net carbon sink. 4) From the mediating effect, the loss of population can cause fluctuations in the agricultural net carbon sink. The improvement of population quality will promote the growth of the agricultural net carbon sink, and the aging of the population will cause the decline of the agricultural net carbon sink. 5) The return of the labor force, the improvement of labor force quality, the improvement of production methods, technological innovation, and skill training are the main ways to increase agricultural net carbon sinks and reduce emissions. This paper can lay a solid foundation for realizing the overall emission reduction target of agricultural production in the Loess Hilly Region.

Effect of stockpiling time on donor-peat hydrophysical properties: Implications for peatland restoration

Northern peatlands are an important global climate regulator storing approximately one-third of the global carbon pool, however the degradation of these ecosystems from land-use change can switch peatlands to persistent and long-term sources of atmospheric carbon dioxide. Active restoration is often required to return degraded peatlands to a net carbon sink. The peat-block restoration technique, where intact peat blocks are extracted from a donor peatland and transferred to restore peatlands where the remnant peat is non-existent, contaminated, and/or undergoes seasonal flooding is increasingly being adopted as a peatland restoration technique given the carbon sequestration that can occur immediately post-restoration. However, donor peat blocks often need to be temporarily stockpiled during the restoration process due to logistical constraints. The dewatering of the peat blocks during this stockpiling period may alter hydrophysical peat properties that sustain critical peatland ecohydrological functionality and ultimately affect peatland restoration success. Yet, the hydrophysical evolution of stockpiled peat blocks remains unknown. Here, we examine how peat block stockpiling time (3, 7, 11, and 14 months and a reference site) impacts peat hydrophysical properties and sphagnum moss photosynthesis, both of which are critical for peatland restoration success. Stockpiling peat differentially impacted the hydrophysical properties between the shallower and deeper peats, where little to no impact from stockpiling was observed in the shallower peats, regardless of stockpiling time. Rather, as stockpiling time increased, there was a marked decrease in macroporosity (pores >75 μm) and mobile porosity (drainable porosity at approximately −100 hpa) at depths below 20 cm but the water conducting matrix porosity (defined as mobile porosity minus macroporosity) was not significantly different than the reference samples. However, stockpiling created inhospitable conditions for sphagnum mosses., as chlorophyll fluorescence ratio was below 0.3, indicating little to no photosynthesis of the stockpiled peat during summertime drought conditions. Taken together, we suggest limiting stockpiling time as much as possible would be advantageous for using the stockpiled peat blocks for the peat-block restoration technique or other restoration efforts, such as floating mat creation.

Renewable butadiene: A case for hybrid processing via bio- and chemo-catalysis

1,3-butadiene (butadiene) is a by-product produced during naphtha steam cracking, predominantly used in tyre manufacturing. Recently, steam crackers have converted to using more cost effective, lighter feedstocks such as shale gas, yielding less butadiene. The potential shortfall, coupled with concerns around increasing greenhouse gas emissions, provides a unique opportunity for renewable production. This study investigated the techno-economics and greenhouse gas emissions associated with renewable butadiene production routes within the context of a China located pulp mill. A hybrid bio-catalytic route, utilising black liquor, was compared against two chemo-catalytic routes using forestry residues and pulpwood. The hybrid bio-catalytic route uses a novel aerobic gas fermentation platform, employing heat integrated supercritical water gasification and aerobic gas fermentation to produce acetaldehyde, followed by chemo-catalytic upgrading (Acet-BD). The two chemo-catalytic routes catalytically upgrade biomass derived syngas; where one route (Eth-BD) passes through an ethanol intermediate, and the other (Syn-BD) utilises a series of commercialised catalytic technologies with propene as an intermediate. The hybrid bio/chemo-catalytic route, Acet-BD, was the only route profitable using the nominal techno-economic inputs, producing a Net Present Value of $2.8 million and Minimum Selling Price of $1367 tn−1. In contrast, the two chemo-catalytic routes produced Minimum Selling Prices of $1954 tn−1 (Eth-BD) and $2196 tn−1 (Syn-BD), demonstrating the competitiveness of this novel platform. Sensitivity analyses highlighted the equipment capital as the main contributor to increased Minimum Selling Price for all cases, and the Acet-BD route presented a 19% probability of achieving a positive net present value. Moreover, owed to the low process emissions and sequestration of biogenic carbon, all routes produced net negative emissions within a cradle-to-gate framework. As such, renewable butadiene production has potential as a net carbon sink for pulp mill residues conventionally destined for energy recovery.

Quantifying Carbon Cycle Extremes and Attributing Their Causes Under Climate and Land Use and Land Cover Change From 1850 to 2300

AbstractThe increasing atmospheric carbon dioxide (CO2) mole fraction affects global climate through radiative (trapping longwave radiation) and physiological effects (reduction of plant transpiration). We use the simulations of the Community Earth System Model (CESM1‐BGC) forced with Representative Concentration Pathway 8.5 to investigate climate‐vegetation feedbacks from 1850 to the year 2300. Human‐induced land use and land cover change (LULCC), through biogeochemical and biogeophysical processes, alter the climate and modify photosynthetic activity. The changing characteristics of extreme anomalies in photosynthesis, referred to as carbon cycle extremes, increase the uncertainty of terrestrial ecosystems to act as a net carbon sink. However, the role of LULCC in altering carbon cycle extremes under business‐as‐usual (continuously rising) CO2 emissions is unknown. Here we show that LULCC magnifies the intensity, frequency, and extent of carbon cycle extremes, resulting in a net reduction in expected photosynthetic activity in the future. We found that large temporally contiguous negative carbon cycle extremes are due to a persistent decrease in soil moisture, which is triggered by declines in precipitation. With LULCC and global warming, vegetation exhibits increased vulnerability to hot and dry environmental conditions, increasing the frequency of fire events and resulting in considerable losses in photosynthetic activity. While most regions show strengthening of negative carbon cycle extremes, a few locations show a weakening effect driven by declining vegetation cover or benign climate conditions for photosynthesis. Increasing hot, dry, and fire‐driven carbon cycle extremes are essential for improving carbon cycle modeling and estimation of ecosystem responses to LULCC and rising CO2 mole fractions. Moreover, large aberrations in vegetation productivity represent potential and growing threats to human lives, wildlife, and food security.

Comment on “Seaweed ecosystems may not mitigate CO2 emissions” by Gallagher et al. (2022)

Abstract The role of animal (and plant) respiration in assessing the true carbon sequestration potential of a system is vital to acknowledge, and addressed in Gallagher et al. (2022). However, within this article, there is confusion around the respiration of kelp once exported to open waters from kelp ecosystems but respired before sequestration. From their consideration of a closed kelp ecosystem (but with import of phytoplankton and export of kelp), respiration of phytoplankton transported into the system is correctly considered in their net respiration figures (but not the fixation of carbon dioxide by the phytoplankton outside the system, again correct for a closed system). However, the respiration of kelp exported from the closed system is also considered as part of the kelp community respiration. A closed system must remove this respiration of exported kelp from calculations. Alternatively, an open system must consider also the carbon fixation by phytoplankton. The outcome of redefining open and closed systems is that the systems examined in Gallagher et al. (2022) will be net sinks of carbon, although, as yet, the magnitude of this sink is poorly quantified.