Carbon Flow Model Research Articles

Carbon metabolism in "production-living-ecological" space in urban agglomeration based on land use change.

To grasp the impact of carbon metabolism on the evolution of "production-living-ecological" (PLE) space due to land usechange in the Changsha-Zhuzhou-Xiangtan (CZT) urban agglomeration, this study delves into the temporal and spatial distribution of PLE space carbon metabolism by constructing a carbon flow model. We evaluate the influence of positive and negative carbon flows on carbon metabolism using ecological network analysis and utility assessment. Furthermore, we delve into the driving factors behind carbon metabolism through redundancy analysis (RDA). The findings of this study included mainly the following aspects. (1) From 2000 to 2020, the net carbon flow in the CZT urban agglomeration consistently remained negative, with the primary source of negative carbon flow being the transition from ecological space to production space. (2) Within the ecological utility network, the dominant ecological relationship shifted from a period of control and exploitation relationship (counted for 61.91%) between 2000 and 2005 to one of competition relationship that counted for 83.33% in 2005-2010, 47.62% in 2010-2015, and 66.67% in 2015-2020. Mutualism relationship, present in the 2000-2005 period, completely disappeared in subsequent years. (3) The value of the utility function M was 0.88, 0.36, 0.48, and 0.40 in four stages (all less than 1), which meant that PLE space evolution on regional carbon metabolism was negative. (4) The key drivers influencing carbon metabolism in PLE space were mainly Change in the Comprehensive Land Use Index (CL), Change in the Proportion of Manufacturing Land (CM), Change in the Proportion of Forestland (CF), and Change in the Proportion of Cultivated Land (CC). Carbon metabolism holds a critical role in the urban material and energy cycle. Studying carbon metabolism within PLE space carries great importance for regional carbon cycling, carbon emission and sequestration, efforts to mitigate climate change, and the maintenance of regional sustainable development.

Analysis of energy, exergy and CO2 emissions in a fiberglass furnace with oxy-fuel combustion

Energy savings and emission reductions in the building materials industry are key components of China’s “dual carbon” goals. A new mathematical model of material, energy, exergy, and carbon flows was established and verified against operational data for an 80600 t/y fiberglass furnace in China. The model enables thermal budget calculation along different paths and analysis of the losses and saving potential of the entire fiberglass melting furnace and its three major subsystems. The results indicated that the selected fiberglass furnace attained a satisfactory performance with a specific energy consumption of 4.63 MJ/kg and an energy efficiency of 74.76%. Oxy-fuel combustion provided a substantial overall fuel reduction relative to air combustion. Moreover, the exergy efficiency and effective exergy efficiency reached 62.85% and 55.23%, respectively. The heat recovery system increased the exergy efficiency by 11.01%. Furthermore, the CO2 emissions associated with glass production, major contributors, CO2 reduction potential, and economic impact were obtained. Finally, a sensitivity analysis of the combustion chamber was conducted. This approach could identify the degree of resource and energy utilization and support the implementation of energy and exergy efficiency improvement and CO2 emission reduction schemes.

Ecological network analysis of the carbon metabolism system in mountainous cities based on the land-carbon nexus: a case study of the main urban area of Chongqing, China.

The analysis of urban carbon metabolism will help to mitigate global warming and achieve China's "Dual Carbon" targets. Taking the main urban area of Chongqing (MUAC) as an example, this study accounted for the carbon release and carbon absorption in MUAC, constructed an urban carbon flow model based on the land-carbon nexus, and evaluated the urban carbon metabolic system from 2000 to 2020 by using the ecological network analysis method. The results show that MUAC is dominated by a "carbon source" effect, and the net carbon flow is always negative. The negative carbon flow mainly comes from the conversion of cultivated land to construction land, and the positive carbon flow mainly comes from the conversion of construction land to cultivated land and woodland. The ecological relationship of carbon metabolism in MUAC is dominated by exploitation and control relationships, which mainly exist in the ecological relationship between construction land and cultivated land, and the spatial distribution is concentrated in the central and western areas of MUAC. Our research results can provide a reference for Chongqing's green and low-carbon sustainable development as a means toward the realization of the "Dual Carbon" targets and provide a reference for other similar mountainous cities in western China.

A stand level scenario model for the Norwegian forestry – a case study on forest management under climate change

Carbon sequestration and income generation are competing objectives in modern forest management. The climate commitments of many countries depend on forests as carbon sinks which must be quantified, monitored, and projected into the future. For projections we need tools to model forest development and perform scenario analyses to assess future carbon sequestration potentials under different management regimes, the expected net present value of such regimes, and possible impacts of climate change. We propose a scenario analysis software tool (GAYA 2.0) that can assist in answering these types of questions using stand level simulations, detailed carbon flow models and an optimizer. This paper has two objectives: (1) to describe GAYA 2.0, and (2) demonstrate its potential in a case study where we analyze the forest carbon balance over a region in Norway based on national forest inventory sample plots. The tool was used to map the optimality front between the carbon benefit and net present value. We observed changes in net present value for different levels of carbon benefit as well as changes in optimal management strategies. We predicted future changes in several forest carbon pools as well as albedo and illustrated the impact of gradual increase in forest productivity (i.e., due to climate warming). Having been updated and modernized from its previous version with increased attention to forest carbon and energy fluxes, GAYA 2.0 is an effective tool that offers multiple opportunities to perform various types of scenario analyses in forest management.

Optimization of Spatial Land Use Patterns with Low Carbon Target: A Case Study of Sanmenxia, China.

Land use change is an important factor in atmospheric carbon emissions. Most of the existing studies focus on modeling the land use pattern for a certain period of time in the future and calculating and analyzing carbon emissions. However, few studies have optimized the spatial pattern of land use from the perspective of the impact of carbon emission constraints on land use structure. Therefore, in this study, the effects of land use change on carbon emissions from 1990 to 2020 were modeled using a carbon flow model for Sanmenxia, Henan, China, as an example. Then, the land use carbon emission function under the low carbon target was constructed, and the differential evolution (DE) algorithm was used to obtain the optimized land use quantity structure. Finally, the PLUS model was used to predict the optimal spatial configuration of land use patterns to minimize carbon emissions. The study produced three major results. (1) From 1990 to 2020, the structural change of land use in Sanmenxia mainly occurred between cultivated land, forest land, grassland and construction land. During this period of land use change, the carbon emissions from construction land first increased and then decreased, but despite the decrease, carbon emissions still exceeded carbon sinks, and the carbon metabolism of land use was still far from equilibrium. (2) Between 2010 and 2020, the area of cultivated land began to decrease, and the area of forest land rapidly increased, and land-use-related carbon emissions showed negative growth. This showed that the structural adjustment of energy consumption in Sanmenxia during the period decreased carbon emissions in comparison with the previous period. (3) A comparison of predicted optimized land use patterns with land use patterns in an as-is development scenario showed a decrease in construction land area of 23.05 km2 in 2030 with a steady increase in forest land area and a decrease in total carbon emission of 20.43 t. The newly converted construction land in the optimized land use pattern was concentrated in the ribbon-clustered towns built during urban expansion along the Shaanling basin of the Yellow River and the Mianchi-Yima industrial development area.

Swimming Activity as an Indicator of Seasonal Diapause in the Copepod Calanus finmarchicus

Copepods dominate zooplankton biomass of the upper ocean, especially in the highly seasonal boreal and polar regions, for which specific life-cycle traits such as the accumulation of lipid reserves, migration into deep water and diapause are key adaptations. Understanding such traits is central to determining the energetic consequences of high latitude range shifts related to climate change and ultimately, biogeochemical models of carbon flow. Using the calanoid copepod Calanus finmarchicus, we explore a new indicator of diapause, swimming activity, and assess its relationship with respiration. Stage CV copepods were sampled in late summer from shallow (epipelagic) and deep (mesopelagic) water at both slope and basin locations within the Fram Strait at a time when the animals had entered diapause. Using high-throughput quantitative behaviour screening on ex-situ swimming activity, we found that irrespective of sampling station copepods from the mesopelagic show highly reduced activity (88.5 ± 3.4% reduction) when compared to those from the epipelagic with a clearly defined threshold between epi- and mesopelagic animals (~5 beam breaks 30 min-1). Mesopelagic individuals were also larger (12.4 ± 8.8%) and had more lipid reserves (19.3 ± 2.2%) than epipelagic individuals. On average, copepods from the basin station exhibited respiration rates similar to overwintering rates observed elsewhere (1.23 ± 0.76 µg C d-1), while respiration rates of copepods from the shelf station were more consistent with active metabolism (2.46 ± 1.02 µg C d-1). Nevertheless, active and diapausing rates were observed in individuals from both stations at both epi- and mesopelagic depths. We suggest that rapid screening of activity may provide an early indicator of diapause before it becomes fully apparent and consistent in other physiological indicators. Ultimately, swimming activity may provide a useful tool to assess the putative endogenous and exogenous factors involved in diapause onset, provide a handle on the energetics of diapause, and input to biogeochemical carbon models on C. finmarchicus.

Rhizosphere effects promote soil aggregate stability and associated organic carbon sequestration in rocky areas of desertification

Soil aggregate stability is an important index for predicting soil water loss and soil erosion resistance. Plant roots effectively control soil erosion and stabilize soil structure, which has a crucial influence on the formation of aggregates and soil organic carbon (SOC) sequestration. We examined how rhizosphere effects influence soil aggregate stability and its associated SOC contents and δ13C values, following a proposed extended model of carbon (C) flows between the aggregate size classes in the root systems based on 13C fractionation in each step of SOC formation. The results show that the rhizosphere effects significantly improved the stability of aggregates. The mean weight diameter (MWD) and geometric mean diameter (GMD) of rhizosphere soil aggregates were significantly higher than those of non-rhizosphere soil aggregates associated with plants with fibrous roots. SOC levels of all size aggregates in the rhizosphere soil of both fibrous and tap root plants were higher than those of non-rhizosphere soil. Moreover, SOC contents increased in the order of silt-clay particles (SCP, <0.05 mm), microaggregates (MIA, 0.05-0.25 mm) and small macroaggregates (SMA, 0.25-1 mm), and then decreased from SMA to large macroaggregates (LMA,> 1 mm). The δ13C values in non-rhizosphere soil were generally higher than those in rhizosphere soil in aggregates of the same size class, especially in the tap root plants. Except for the rhizosphere soil of fibrous root plants, the other three soil types (rhizosphere and non-rhizosphere soil of tap root plants, and non-rhizosphere soil of fibrous root plants) were shown to have aggregate δ13C values that decreased with increasing soil aggregate size. Δ13C enrichment of the SOC fractions showed that the general flow direction of SOC was from rhizosphere to non-rhizosphere, and from large aggregates to small aggregates. The C flow in the aggregates of rhizosphere soil was clearly greater than that in the non-rhizosphere soil, especially with the fibrous root plants. These findings suggest that plant roots have the potential to regulate soil structural stability, and enhance soil erosion resistance and SOC sequestration.

CPlantBox, a whole-plant modelling framework for the simulation of water- and carbon-related processes

Abstract The interaction between carbon and flows within the vasculature is at the centre of most growth and developmental processes. Understanding how these fluxes influence each other, and how they respond to heterogeneous environmental conditions, is important to answer diverse questions in agricultural and natural ecosystem sciences. However, due to the high complexity of the plant–environment system, specific tools are needed to perform such quantitative analyses. Here, we present CPlantBox, a whole-plant modelling framework based on the root system model CRootBox. CPlantBox is capable of simulating the growth and development of a variety of plant architectures (root and shoot). In addition, the flexibility of CPlantBox enables its coupling with external modelling tools. Here, we connected the model to an existing mechanistic model of water and carbon flows in the plant, PiafMunch. The usefulness of the CPlantBox modelling framework is exemplified in five case studies. Firstly, we illustrate the range of plant structures that can be simulated using CPlantBox. In the second example, we simulated diurnal carbon and water flows, which corroborates published experimental data. In the third case study, we simulated impacts of heterogeneous environment on carbon and water flows. Finally, we showed that our modelling framework can be used to fit phloem pressure and flow speed to (published) experimental data. The CPlantBox modelling framework is open source, highly accessible and flexible. Its aim is to provide a quantitative framework for the understanding of plant–environment interaction.

A multi-biomarker approach supports the use of compound-specific stable isotope analysis of amino acids to quantify basal carbon source use in a salt marsh consumer.

Determining the flow of energy from primary producers to higher trophic levels in complex systems remains an important task for ecologists. Biomarkers can be used to trace carbon or energy sources contributing to an organism's tissues. However, different biomarkers vary in their ability to trace carbon sources based on how faithfully they transfer between trophic levels. Comparing emerging biomarker techniques with more commonly used techniques can demonstrate the relative efficacy of each in specific systems. Two common biomarker techniques, fatty acid analysis (FAA) and bulk stable isotope analysis (SIA), and one emerging biomarker technique, compound-specific stable isotope analysis of amino acids (CSIA-AA), were compared to assess their ability to characterize and quantify basal carbon sources supporting the seaside sparrow (Ammodramus maritimus), a common salt marsh species. Herbivorous insect and deposit-feeding fiddler crab biomarker values were analyzed as proxies of major terrestrial and aquatic basal carbon sources, respectively. All three biomarker techniques indicated that both terrestrial and aquatic carbon sources were important to seaside sparrows. However, FAA could only be evaluated qualitatively, due to a currently limited understanding of trophic modification of fatty acids between primary producer and this consumer's tissues. Quantitative stable isotope (SIA or CSIA-AA) mixing models predicted nearly equal contributions of terrestrial and aquatic carbon sources supporting seaside sparrows, yet estimates based on CSIA-AA had greater precision. These findings support the use of CSIA-AA as an emerging tool to quantify the relative importance of basal carbon sources in salt marsh consumers. Integrating multiple biomarker techniques, with their differing benefits and limitations, will help to constrain models of carbon and energy flow in future ecosystem studies.

An empirical model of carbon flow through marine viruses and microzooplankton grazers.

Viruses and microzooplankton grazers represent major sources of mortality for marine phytoplankton and bacteria, redirecting the flow of organic material throughout the world's oceans. Here, we investigate the use of nonlinear population models of interactions between phytoplankton, viruses and grazers as a means to quantitatively constrain the flow of carbon through marine microbial ecosystems. We augment population models with a synthesis of laboratory-based estimates of prey, predator and viral life history traits that constrain transfer efficiencies. We then apply the model framework to estimate loss rates in the California Current Ecosystem (CCE). With our empirically parameterized model, we estimate that, of the total losses mediated by viruses and microzooplankton grazing at the focal CCE site, 22 ± 3%, 46 ± 27%, 3 ± 2% and 29 ± 20% were directed to grazers, sloppy feeding (as well as excretion and respiration), viruses and viral lysate respectively. We identify opportunities to leverage ecosystem models and conventional mortality assays to further constrain the quantitative rates of critical ecosystem processes.

Constructing the Embodied Carbon Flows and Emissions Landscape from the Perspective of Supply Chain

From the perspective of supply chain, benchmarking the embodied carbon flows and emissions landscape is to study the carbon footprint in supply chain production and process management. On the basis of the theory of a green supply chain, this paper conducted its research through the following steps. First, a multi-level supply chain model was proposed and established, and various sectors, production and management processes, and inputs and outputs of different resources were integrated into the supply chain network, and then divided into multiple levels. Second, a multi-level embodied carbon flow and emissions model was established through the Leontief Inverse. Third, based on the operation data of forestry-pulp and paper companies, the embodied carbon flows and emissions at all levels and sectors were estimated and analyzed. Finally, the dismantling and processing methods of complex carbon network structures were explored, the hot-spot carbon sources and paths were obtained, and the low-carbon innovation and development strategies were proposed. The research results show that: (1) Supply chain is a new idea and carrier to study the spatial and state changes of carbon, and also provides a platform for spatial landscape analysis of carbon; (2) The modeling and calculation of carbon flows and emissions offer a new solution of evaluating the environmental performance of companies with high pollution and emission such as forestry-pulp and paper companies, and provide the government effective technical support to implement environmental regulations and formulate carbon emission reduction policies.

Evaluation and simulation of the impact of land use change on ecosystem services based on a carbon flow model: A case study of the Manas River Basin of Xinjiang, China

Land use change affects ecosystem services by changing the structure and function of ecosystems. Carbon flows throughout natural and socioeconomic systems can effectively reveal this process. The Manas River Basin has experienced rapid oasis expansion for decades, and land use change in the basin is very typical. Oasis expansion has caused a large amount of cropland to invade natural vegetation, thus affecting ecosystem services. This study used a biomass-based ecosystem service estimation model to assess changes in ecosystem services in the Manas River Basin. The carbon flow model was constructed using energy systems language, and the future development of ecosystem services was simulated based on different land use scenarios. The results show the following: (1) From 1980 to 2015, the river basin provisioning service was continuously optimized, while the regulating, supporting and cultural services were reduced. (2) If the expansion of cropland continues, then carbon will be transferred from the natural ecosystem to the cropland. Regulation, support and cultural services in the basin continue to decrease. Due to the shortage of water resources in the basin, the growth of provisioning services is limited. (3) If the project of returning cropland to grassland is implemented, then the carbon in the natural ecosystem will gradually recover. The regulating, supporting and cultural services of the river basin are rising, but provisioning services are gradually decreasing. In general, the model based on energy systems language can reflect the ecological process within the system and effectively reveal the carbon flow process between ecosystems. The use of carbon to quantify ecosystem services can harmonize dimensions, facilitate comparisons, and mitigate errors in outcomes due to different evaluation criteria or subjective factors. Therefore, this study combines energy systems language with carbon flow, which helps to more rationally explore the impact of land use change on ecosystem services, thereby providing valuable information for river basin management.

Carbon element flow analysis and CO2 emission reduction in iron and steel works

As an intensive energy-consuming and carbon-emitting industry, iron and steel manufacturing is vital for meeting the energy conservation and CO2 emission reduction targets of China. A set of methods has been presented to quantify CO2 emission, however, no unified standards are available for the iron and steel industry yet. To analyze the CO2 emission-affecting factors, a carbon flow model and a corresponding calculation method are proposed with consideration of the relationship among emission factor, system boundary, and index. Then, a case study is conducted in two iron and steel mills in China, and carbon element flow diagrams are mapped out graphically. The CO2 emission-affecting factors were analyzed based on material flow analysis. The results show that the Specific CO2 emission of two case mills with different material flows and electricity consumption structures are 2035.06 kg/t-cs and 2497.21 kg/t-cs, respectively. Purchased scrap recycled to basic oxygen furnace reduces the CO2 emission dramatically. By contrast, self-produced scrap, which is controlled by the production yield, increases the emission. Specific CO2 emission decreases dramatically with the reducing of OPP generation rate, maximum reduction can be up to 334.80 kg/t-cs. Using natural gas or steam coal as substitute for BFG consumed in onsite power plant, Specific CO2 emission can be reduced by 299.22 kg/t-cs and 86.97 kg/t-cs, respectively.

Carbon capture and storage in branching stage alfalfa (Medicago sativa L.) by 13C pulse labeling

AbstractIn the present study, we investigated the absorption and transfer of photosynthetic carbon among the different alfalfa parts. Alfalfa was planted under controlled conditions and pulse‐labeled with carbon–13 dioxide (13CO2; gas) during its branching stage. Then, the amounts of 13CO2 on the alfalfa leaves, stems and roots were measured, and soil samples were taken after 6, 12, 18, 24 and 30 days. The carbon‐13 (13C) distribution ratios of roots, stems and leaves increased over the sampling time and reached the maximum value at day 18; after that, the values decreased but still higher than day 6 and day 12. The 13C distribution ratio in the roots increased gradually to 2.77% at day 30. Over the extended labeling time, 13C loss caused by root and microbial respiration increased. There was no clear trend visible in the 0–10 cm soil layer, but in the 10–20 cm soil layer, the 13C distribution ratio increased gradually from 2.46% at day 6 to 3.05% at day 30. The 13C content in the 0–10 cm soil layer at days 6, 12, 18, 24 and 30 after labeling ranged from 0.90 ppm to 1.53 ppm and in the 10–20 cm layer increased from 0.83 ppm (6 days) to 1.12 ppm (30 days). The 13CO2 released by microbial respiration increased gradually from 2.02 mg at day 6 to 23.30 mg at day 30. The 13CO2 content released by alfalfa root respiration accounted for the majority of total respired 13C content and increased from 24.06 mg (6 days) to 54.15 mg (18 days) and remained constant hereafter. This study suggests that carbon was rapidly cycled between the different parts of alfalfa and soil by means of photosynthesis and respiration. The results obtained in this study will be of importance for building the mechanistic model of photosynthetic carbon flow in alfalfa‐soil system.

Dry season limnological conditions and basin geology exhibit complex relationships with δ13C and δ15N of carbon sources in four Neotropical floodplains

Studies in freshwater ecosystems are seeking to improve understanding of carbon flow in food webs and stable isotopes have been influential in this work. However, variation in isotopic values of basal production sources could either be an asset or a hindrance depending on study objectives. We assessed the potential for basin geology and local limnological conditions to predict stable carbon and nitrogen isotope values of six carbon sources at multiple locations in four Neotropical floodplain ecosystems (Paraná, Pantanal, Araguaia, and Amazon). Limnological conditions exhibited greater variation within than among systems. δ15N differed among basins for most carbon sources, but δ13C did not (though high within-basin variability for periphyton, phytoplankton and particulate organic carbon was observed). Although δ13C and δ15N values exhibited significant correlations with some limnological factors within and among basins, those relationships differed among carbon sources. Regression trees for both carbon and nitrogen isotopes for all sources depicted complex and in some cases nested relationships, and only very limited similarity was observed among trees for different carbon sources. Although limnological conditions predicted variation in isotope values of carbon sources, we suggest the resulting models were too complex to enable mathematical corrections of source isotope values among sites based on these parameters. The importance of local conditions in determining variation in source isotope values suggest that isotopes may be useful for examining habitat use, dispersal and patch dynamics within heterogeneous floodplain ecosystems, but spatial variability in isotope values needs to be explicitly considered when testing ecosystem models of carbon flow in these systems.

Planktons in Dirty Water: Carbon Cycling Process of Sewage Fed Fisheries in East Kolkata Wetland, India

East Kolkata Wetland (EKW), a Ramsar site located in West Bengal, India is unique in the world as domestic city sewage is utilized here by the fishermen as fish feed. It is important to understand the nutrient cycling pathways of this unique ecosystem in relation to the biotic communities in order to assess its health and sustainability. This study examined plankton community structure in relation to the nutrient cycling pathways and various abiotic parameters of the sewage fed fisheries of EKW in comparison to the control ponds. RDA analysis show alkalinity and water temperature are the major environmental regulators controlling phytoplankton and zooplankton communities. Results of backward stepwise linear regression indicate dissolve carbon di-oxide and water pH play important role in gross primary production in sewage fed system. As plankton communities play an important role in transport and conversion of various carbon forms like soil organic carbon, particulate organic carbon, dissolve carbon di-oxide and soil inorganic carbon, the current study has presented a conceptual model of carbon flow in the EKW fish ponds and suggests replicability of such system elsewhere for city sewage management.

Carbon dynamics modelization and biological community sensitivity to temperature in an oligotrophic freshwater Antarctic lake

Lake Limnopolar, located in one of the areas on Earth experiencing the strongest local warming, has been studied as a maritime Antarctic lake model by the Limnopolar Research Team during the last decade. Data collected during this period revealed the existence of an important meteorological interannual variability in the area of Byers Peninsula. With the aim of increasing the knowledge of this ecosystem and its sensibility to climate change as a model ecosystem, as well as to calibrate the extent of the interannual variability, a carbon flow model was developed partly describing its microbial food web. This preliminary model aims to describe part of the carbon dynamics, especially for bacterioplankton and associated factors, in this maritime Antarctic lake highly affected by temperature increase linked to regional warming. To describe the system, the effects of the variation of different forcing functions influencing the carbon flow within the microbial community, like temperature and irradiance, were studied. Among the studied factors, the sensitivity analysis showed the strongest response of the model to temperature changes. Consumption rates of organic matter by bacterioplankton, and therefore its abundance in lake water, greatly increased when temperature rise was higher. However, the highly variable meteorology over years in such an extreme environment causes that our model may fit well for some years, but fails to describe the system in years with contrasting meteorological conditions. Despite this assumption, the model reveals that maritime Antarctic lakes are very sensitive to temperature changes. This response can be monitored using eco-exergy, which allows a description of the system complexity. Due to this temperature sensitivity, the warming occurring in this area would lead to significant changes in the carbon flow, and consequently on the abundance of plankton in these systems.

An integrated approach to modeling changes in land use, land cover, and disturbance and their impact on ecosystem carbon dynamics: a case study in the Sierra Nevada Mountains of California

Increased land-use intensity (e.g. clearing of forests for cultivation, urbanization), often results in the loss of ecosystem carbon storage, while changes in productivity resulting from climate change may either help offset or exacerbate losses. However, there are large uncertainties in how land and climate systems will evolve and interact to shape future ecosystem carbon dynamics. To address this we developed the Land Use and Carbon Scenario Simulator (LUCAS) to track changes in land use, land cover, land management, and disturbance, and their impact on ecosystem carbon storage and flux within a scenario-based framework. We have combined a state-and-transition simulation model (STSM) of land change with a stock and flow model of carbon dynamics. Land-change projections downscaled from the Intergovernmental Panel on Climate Change’s (IPCC) Special Report on Emission Scenarios (SRES) were used to drive changes within the STSM, while the Integrated Biosphere Simulator (IBIS) ecosystem model was used to derive input parameters for the carbon stock and flow model. The model was applied to the Sierra Nevada Mountains ecoregion in California, USA, a region prone to large wildfires and a forestry sector projected to intensify over the next century. Three scenario simulations were conducted, including a calibration scenario, a climate-change scenario, and an integrated climate- and land-change scenario. Based on results from the calibration scenario, the LUCAS age-structured carbon accounting model was able to accurately reproduce results obtained from the process-based biogeochemical model. Under the climate-only scenario, the ecoregion was projected to be a reliable net sink of carbon, however, when land use and disturbance were introduced, the ecoregion switched to become a net source. This research demonstrates how an integrated approach to carbon accounting can be used to evaluate various drivers of ecosystem carbon change in a robust, yet transparent modeling environment.

Biofuel’s carbon balance: doubts, certainties and implications

Liquid fuels will remain valued energy carriers well into any upcoming period when CO2 reductions are sought. Biofuels are the presumed replacement for the petroleum-based transportation fuels that dominate liquid fuel use. Lifecycle analysis embeds a closed-loop model of biofuel-related carbon flows, making net CO2 uptake an assumption to be refuted. However, evaluating net CO2 uptake through dynamic industrial and agriforestry supply chains at real-world commercial scales is extremely difficult. All such estimates carry a great deal of doubt and cannot be verified empirically. A different perspective follows by anchoring analysis inthecertaintythatend-useCO2emissionsfrombiofuelsareessentiallythesameasthoseofthe petroleum fuels they replace. A first-order model of the globally coupled bio- and fossil-fuel system reveals conditions for biofuel use to provide an atmospheric benefit. No benefit occurs in theenergysectorswherebiofuelsareused,butrather must be foundelsewhereinlocationsof carbonabsorptionorretention.Theimplicationisthatclimatemitigationeffortsshouldfocuson such locations and include any mechanisms through which net uptake (an enhanced sink or verifiable offset) can be achieved by biological, chemical, geological or other means. Although biofuels can play a mitigation role when certain conditions are met, deemphasizing biofuel production in favor of terrestrial carbon management may offer more immediate and effective ways to counterbalance the CO2 emitted when using carbon-based liquid fuels of any origin. Climate policies for transportation fuels should be reconsidered accordingly.

Carbon flows in the benthic food web of the Porcupine Abyssal Plain: The (un)importance of labile detritus in supporting microbial and faunal carbon demands

Carbon flows in the benthic food web of the Porcupine Abyssal Plain (4850 m, northeast Atlantic) were reconstructed using linear inverse modeling based on mass balances of the various compartments, biomass data, carbon flux measurements, physiological constraints, and data from a previously published 13C‐phytodetritus pulse‐chase experiment. Food web compartments consisted of bacteria, Foraminifera, three feeding types of nematodes and of macrofauna, and four feeding types of megafauna. Three lability classes of detritus were defined to clarify especially the possible role of labile detritus in this abyssal plain food web. Total detritus inputs to the food web were 0.56 mmol C m−2 d−1, with only a minor (3.8%) contribution of labile detritus. The dominant pathway in the food web was dissolution of more refractory detritus, uptake by bacteria, and subsequent respiration (0.36 mmol C m−2 d−1, 80% of the community respiration). Lower contributions to community respiration were found for surface‐deposit‐feeding macrobenthos (5.6%), Foraminifera (4.9%), predatory macrobenthos (3.8%), and other deposit‐feeding macrobenthos (3.1%). Contributions by other benthic compartments were &lt; 1%. 13C‐phytodetritus transfer data strongly constrained the carbon source for bacteria, Foraminifera, and the nematode and macrobenthic compartments. Surprisingly, labile detritus contributed &lt; 5% of the total carbon requirements for all these compartments. Carbon sources were much less constrained for the megabenthic compartments because for these compartments no 13C pulse‐chase data were available. The carbon flow model evidently shows a limited role of labile detritus in the food web.