Sequestration Of Atmospheric CO2 Research Articles

Sequestration of atmospheric CO2 in boreal forest carbon pools in northeastern China: Effects of nitrogen deposition

An increase in nitrogen (N) deposition has been proposed to cause boreal forests to capture and store a globally significant quantity of carbon (C), but the size of the boreal forest C sink remains uncertain after N addition. Therefore, we conducted a N addition experiment using four N addition rates (0, 2.5, 5.0 and 7.5gNm−2yr−1) in the boreal zone of northeastern China to determine the changes in forest C sequestration and to investigate the mechanisms of the changes in C sequestration after N addition. Our data show that N addition increases the total C sequestration, but the efficiency of this effect is reduced as the N addition rate increases. We also found that the amount and the mechanism of the C sequestration increase in above- and belowground C pools vary with different amounts of N addition. Low- and medium-N addition increased the above- and belowground C sequestration, and the potential mechanisms responsible for such C accumulation include N-induced increases in photosynthesis via a decrease in the foliar C content and increases in root mass via increased plant C allocation in the roots. However, high-N addition decreases aboveground C sequestration by inhibiting photosynthesis and increases belowground C sequestration by inhibiting soil C losses. Our data indicate that the response patterns of above- and belowground C pools to different amounts of N addition may involve several complex biochemical processes and occur by different mechanisms; therefore, separating the effects of N addition on above- and belowground C sequestration will help improve and validate current modeling efforts.

Post-glacial climate forcing of surface processes in the Ganges–Brahmaputra river basin and implications for carbon sequestration

Climate has been proposed to control both the rate of terrestrial silicate weathering and the export rate of associated sediments and terrestrial organic carbon to river-dominated margins – and thus the rate of sequestration of atmospheric CO2 in the coastal ocean – over glacial–interglacial timescales. Focused on the Ganges–Brahmaputra rivers, this study presents records of post-glacial changes in basin-scale Indian summer monsoon intensity and vegetation composition based on stable hydrogen (δD) and carbon (δ13C) isotopic compositions of terrestrial plant wax compounds preserved in the channel–levee system of the Bengal Fan. It then explores the role of these changes in controlling the provenance and degree of chemical weathering of sediments exported by these rivers, and the potential climate feedbacks through organic-carbon burial in the Bengal Fan. An observed 40‰ shift in δD and a 3–4‰ shift in both bulk organic-carbon and plant-wax δ13C values between the late glacial and mid-Holocene, followed by a return to more intermediate values during the late Holocene, correlates well with regional post-glacial paleoclimate records. Sediment provenance proxies (Sr, Nd isotopic compositions) reveal that these changes likely coincided with a subtle focusing of erosion on the southern flank of the Himalayan range during periods of greater monsoon strength and enhanced sediment discharge. However, grain-size-normalized organic-carbon concentrations in the Bengal Fan remained constant through time, despite order-of-magnitude level changes in catchment-scale monsoon precipitation and enhanced chemical weathering (recorded as a gradual increase in K/Si⁎ and detrital carbonate content, and decrease in H2O+/Si⁎, proxies) throughout the study period. These findings demonstrate a partial decoupling of climate change and silicate weathering during the Holocene and that marine organic-carbon sequestration rates primary reflect rates of physical erosion and sediment export as modulated by climatic changes. Together, these results reveal the magnitude of climate changes within the Ganges–Brahmaputra basin following deglaciation and a closer coupling of monsoon strength with OC burial than with silicate weathering on millennial timescales.

Converting highly productive arable cropland in Europe to grassland: \u2013a poor candidate for carbon sequestration

Sequestration of atmospheric CO2 as organic carbon by agricultural soils (SOC) is promoted as a climate change mitigation option. IPCC provides guidelines for determining carbon stocks and sequestration potential, incentivising policy changes towards management of farmland for carbon sequestration. However, the basis of the assumption that agricultural soils can sequester significant atmospheric CO2 has been questioned. We sought to determine the potential for conversion of arable cropland to grassland to sequester carbon in the short to medium term and potential limiting factors. There were no differences in SOC stocks in the top 30 cm between grassland up to 17 years old and arable cropland at 14 sites across the UK. However, SOC showed different distribution patterns, being concentrated in the top 10 cm under grassland. Soil microbial communities were significantly different between arable and grassland, with higher biomass and lesser dominance by bacteria in grassland soils. A land use conversion experiment showed these changes occurred within one year of land use change. Failure of grassland soils to accumulate SOC was attributed to reduced available soil nitrogen, resulting in low productivity. The implications of these results for carbon sequestration in soils as a climate change mitigation strategy are discussed.

Effects of short-term N addition on soil C fluxes in alpine Sibiraea angustata scrub on the eastern margin of the Qinghai-Tibetan Plateau

Although knowledge of the impact of N enrichment on soil C fluxes is scant, such information is highly critical for estimating the global C budget under elevated N deposition. To quantify the effects of short-term N addition on soil C sequestration in an alpine scrub ecosystem, we conducted a field experiment for Sibiraea angustata scrub on the eastern margin of the Qinghai-Tibetan Plateau in China. We quantified the soil C pool (0–30cm) and C fluxes in litterfall, fine root (<2mm diameter) production (FRP), and soil CO2 emission (heterotrophic respiration, Rh) over four years with four levels of N addition (N0; control, N20; 20, N50; 50, and N100, 100kgNha−1year−1). The results showed that at control plots the total C-input (433±33gCm−2year−1) via FRP (360±34gCm−2year−1) and litterfall (73±1gCm−2year−1) was close to the C-output via Rh (466±5gCm−2year−1), which demonstrates that the S. angustata scrub soil C is at equilibrium status. However, adding N, particularly the N100 treatment, significantly affected the soil C balance; the soil became a C sink (163±46gCm−2year−1) by increasing FRP (+63%) rather than by increasing litterfall (P>0.05) or reducing Rh (P>0.05). As a result, the soil C pool (0–30cm) increased significantly. In conclusion, these results suggest that fine roots play a dominant role in the C balance of an alpine scrub ecosystem due to large C-inputs to the soil. Moreover, short-term high N enrichment causes sequestration of additional atmospheric CO2, largely because of the stimulation of fine root growth rather than increased inputs of aboveground plant litterfall or reductions in soil CO2 emission.

Sundarban mangroves: diversity, ecosystem services and climate change impacts

The Bengal delta coast harboring the famous Sundarban mangroves is extremely vulnerable to climate change. Already, salinity intrusion, increasing cyclones and anomalies in rainfall, and temperature, are causing many social and livelihood problems. However, our knowledge on the diversified climate change impacts on Sundarban ecosystems services, providing immense benefits, including foods, shelters, livelihood, and health amenities, is very limited. Therefore, this article has systematically reviewed the major functional aspects, and highlights on biodiversity, ecosystem dynamics, and services of the Sunderban mangroves, with respect to variations in climatic factors. The mangrove ecosystems are highly productive in terms of forest biomass, and nutrient contribution, especially through detritus-based food webs, to support rich biodiversity in the wetlands and adjacent estuaries. Sundarban mangroves also play vital role in atmospheric CO2 sequestration, sediment trapping and nutrient recycling. Sea level rise will engulf a huge portion of the mangroves, while the associated salinity increase is posing immense threats to biodiversity and economic losses. Climate-mediated changes in riverine discharge, tides, temperature, rainfall and evaporation will determine the wetland nutrient variations, influencing the physiological and ecological processes, thus biodiversity and productivity of Sundarban mangroves. Hydrological changes in wetland ecosystems through increased salinity and cyclones will lower the food security, and also induce human vulnerabilities to waterborne diseases. Scientific investigations producing high resolution data to identify Sundarban?s multidimensional vulnerabilities to various climatic regimes are essential. Sustainable plans and actions are required integrating conservation and climate change adaptation strategies, including promotion of alternative livelihoods. Thus, interdisciplinary approaches are required to address the future climatic disasters, and better protection of invaluable ecosystem services of the Sunderban mangroves.Asian J. Med. Biol. Res. December 2016, 2(4): 488-507

More reducing bottom-water redox conditions during the Last Glacial Maximum in the southern Challenger Deep (Mariana Trench, western Pacific) driven by enhanced productivity

The modern southern Mariana Trench is characterized by oligotrophic surface waters, resulting in low primary productivity and well-oxygenated bottom waters. This study investigates changes in the redox conditions of bottom waters in the southern Mariana Trench during the Last Glacial Maximum (LGM) and their potential causes. We measured major, trace, and rare earth elements (REE) in three gravity cores (GC03, GC04, and GC05) and one box core (BC11) retrieved from the southern Challenger Deep at water depths from 5289 to 7118m. The upper sediment layers of both GC05 and BC11 are dominated by valve fragments of the giant diatom Ethmodiscus rex, forming laminated diatom mats (LDMs). 14C-AMS dates of bulk organic matter show that the LDMs accumulated between 18.4 and 21.8 kyr B.P., corresponding to the LGM. Modest enrichments of U and Mo along with weak or absent Ce anomalies in the LDM point to suboxic conditions during the LGM. In contrast, non-LDM samples exhibit little to no enrichment of redox-sensitive elements as well as negative Ce anomalies, indicating deposition under oxic bottom-water conditions. The Ce anomalies are considered valid proxies for bottom-water redox conditions because REE signatures were acquired in the early diagenetic environment, as indicated by strong P-REE correlations and middle-REE enrichment associated with early diagenetic cycling of Fe-Mn oxyhydroxides in the sediment column followed by capture of the REE signal by biogenic and/or authigenic apatite. We postulate that the more reducing bottom-water conditions during the LGM were linked to increased primary productivity induced by enhanced Asian dust input. As shown in earlier studies, the increased primary productivity associated with Ethmodiscus rex blooms in the eastern Philippine Sea played a significant role in capturing atmospheric CO2 during the LGM. Consequently, the magnitude of atmospheric CO2 sequestration by giant diatom blooms during the LGM may have been greater than previously envisaged.

Microalgae as embedded environmental monitors

In marine ecosystems, microalgae are an important component as they transform large quantities of inorganic compounds into biomass and thereby impact environmental chemistry. Of particular relevance is phytoplankton's sequestration of atmospheric CO2, a greenhouse gas, and nitrate, one cause of harmful algae blooms. On the other hand, microalgae sensitively respond to changes in their chemical environment, which initiates an adaptation of their chemical composition. Analytical methodologies were developed in this study that utilize microalgae's adaptation as a novel approach for in-situ environmental monitoring. Longterm applications of these novel methods are investigations of environmental impacts on phytoplankton's sequestration performance and their nutritional value to higher organisms feeding on them.In order to analyze the chemical composition of live microalgae cells (Nannochloropsis oculata), FTIR-ATR spectroscopy has been employed. From time series of IR spectra, the formation of bio-sediment can be monitored and it has been shown that the nutrient availability has a small but observable impact. Since this bio-sediment formation is governed by several biological parameters of the cells such as growth rate, size, buoyancy, number of cells, etc., this enables studies of chemical environment's impact on biomass formation and the cells' physical parameters.Moreover, the spectroscopic signature of these microalgae has been determined from cultures grown under 25 different CO2 and NO3− mixtures (200 ppm-600 ppm CO2, 0.35 mM-0.75 mM NO3−). A novel, nonlinear modeling methodology coined ‘Predictor Surfaces’ is being presented by means of which the nonlinear responses of the cells to their chemical environment could reliably be described. This approach has been utilized to measure the CO2 concentration in the atmosphere over the phytoplankton culture as well as the nitrate concentration dissolved in their growing environment. The achieved precision of concentration predictions were a few percent of the measurement range. Moreover, the Predictor Surface itself allows for a chemical interpretation of the cells' response to a shift in their chemical environment. This will open new approaches to study the link between concentration levels in an ecosystem and the biological consequences for this ecosystem.

Travertines Associated With Hyperalkaline Springs: Evaluation As A Proxy For Paleoenvironmental Conditions And Sequestration of Atmospheric CO 2

Abstract: Travertine are found in ophiolite massifs in association with bicarbonate-depleted hyperalkaline spring waters (pH up to 11.9), in contrast with most continental carbonates (e.g., travertine, tufa, speleothems) that precipitate from calcium bicarbonate-enriched waters. Here travertines formed from bicarbonate-depleted hyperalkaline spring water were subjected to a multidisciplinary and multi-scale approach to evaluate their potential as proxies of past climatic records and sequestration of atmospheric CO 2 . Two mechanisms of calcium carbonate precipitation were apparent: 1) hydration-hydroxylation reaction due to the mixing of hyperalkaline and surface runoff waters, or 2) dissolution of atmospheric CO 2(g) into hyperalkaline waters. For two sites, the bulk chemical signature of travertines (Mg, Ca, and Sr wt%) are consistent with “prior calcite precipitation” (PCP) processes and thus likely records the environmental conditions at the time of their formation. However, for the third site, the trace-element concentrations in the various carbonate fabrics indicate some recrystallization. Constant δ 18 O values indicate that hydration and hydroxylation reactions completely buffer the oxygen isotope composition of the water (equilibrium state) from which a paleo-temperature can be estimated. In contrast, δ 13 C values reflect potential carbon sources, either from surface runoff waters or atmospheric CO 2 . Within the framework of continental carbonate, calcium carbonate formation in bicarbonate-depleted hyperalkaline environments results in a linear and positive co-variation of δ 18 O and δ 13 C values and defines a unique and distinctive stable-isotope field on a δ 18 O–δ 13 C plot, in contrast to carbonates formed in more typical bicarbonate-enriched environments. Moreover, the combined variations in δ 18 O, δ 13 C, and 87 Sr/ 86 Sr between laminae document the changes in the paleo-activity of hyperalkaline spring and surface runoff waters on the time scale of formation. The 87 Sr/ 86 Sr ratio represents a tracer for quantifying surface runoff water contribution. Furthermore, the amount of CO 2 sequestrated in travertine has been estimated following different scenarios of formation. The calculated CO 2 sequestrated for these deposits ranges from 9 kgCO 2 yr –1 to 522 kgCO 2 yr –1 .

Soil health and carbon management

AbstractSoil, a natural four‐dimensional body at the atmosphere–lithosphere interface, is organic‐carbon‐mediated realm in which solid, liquid, and gaseous phases interact at a range of scales and generate numerous ecosystem goods and services. Soil organic carbon (SOC) strongly impacts soil quality, functionality and health. Terms soil quality and soil health should not be used interchangeable. Soil quality is related to what it does (functions), whereas soil health treats soil as a living biological entity that affects plant health. Through plant growth, soil health is also connected with the health of animals, humans, and ecosystems within its domain. Through supply of macro‐ and micronutrients, soil health, mediated by SOC dynamics is a strong determinant of global food and nutritional security. Soil C pool consists of two related but distinct components: SOC and soil inorganic C (SIC). The SIC pool comprises of primary and secondary carbonates, and the latter consists of calcitic (no net sequestration of atmospheric CO2) and silicatic (net sequestration). While SOC is highly dynamic, its mean residence time depends on the degree of protection (physical, chemical, biological, and ecological) within the soil matrix. Formation of stable microaggregates and of organo–mineral complexes can protect SOC against microbial processes for millennia. In addition to formation of silicatic type of secondary carbonates, leaching of bicarbonates into the subsoil or shallow water table is also an important mechanism of sequestration of CO2 as SIC. Numerous soil functions and ecosystem services depend on SOC and its dynamics. Improvements in soil health, along with increase in availability of water and nutrients, increases soil's resilience against extreme climate events (e.g., drought, heat wave) and imparts disease‐suppressive attributes. Enhancing and sustaining soil health is also pertinent to advancing Sustainable Development Goals of the U.N. such as alleviating poverty, reducing hunger, improving health, and promoting economic development.

Experimental Climate Change Modifies Degradative Succession in Boreal Peatland Fungal Communities.

Peatlands play an important role in global climate change through sequestration of atmospheric CO2. Climate-driven changes in the structure of fungal communities in boreal peatlands that favor saprotrophic fungi can substantially impact carbon dynamics and nutrient cycling in these crucial ecosystems. In a mesocosm study using a full factorial design, 100 intact peat monoliths, complete with living Sphagnum and above-ground vascular vegetation, were subjected to three climate change variables (increased temperature, reduced water table, and elevated CO2 concentrations). Peat litterbags were placed in mesocosms, and fungal communities in litterbags were monitored over 12months to assess the impacts of climate change variables on peat-inhabiting fungi. Changes in fungal richness, diversity, and community composition were assessed using Illumina MiSeq sequencing of ribosomal DNA (rDNA). While general fungal richness reduced under warming conditions, Ascomycota exhibited higher diversity under increased temperature treatments over the course of the experiment. Both increased temperature and lowered water table position drove shifts in fungal community composition with a strong positive effect on endophytic and mycorrhizal fungi (including one operational taxonomic unit (OTU) tentatively identified as Barrenia panicia) and different groups of saprotrophs identified as Mortierella, Galerina, and Mycena. These shifts were observed during a predicted degradative succession in the decomposer community as different carbon substrates became available. Since fungi play a central role in peatland communities, increased abundances of saprotrophic fungi under warming conditions, at the expense of reduced fungal richness overall, may increase decomposition rates under future climate scenarios and could potentially aggravate the impacts of climate change.

Gypsum application increases the carbon stock in soil under sugar cane in the Cerrado region of Brazil

Gypsum is widely used in agriculture in the Cerrado region of Brazil to increase root volume and distribution in the profile of predominantly acidic soils with high aluminium toxicity. The gypsum-induced increase in the root system may be an effective strategy to increase sequestration of atmospheric CO2. However, few studies have investigated the relationship between the use of gypsum and carbon accumulation in the soil under sugar cane. In the present study, total carbon stock (TC) in the soil and its fractions were estimated after four growing seasons of sugar cane under gypsum application. The experiment was arranged in a randomised block design with four replicates and two treatments: control (0Mgha–1) and the technically recommended rate of gypsum application (5Mgha–1). Sugarcane stalk biomass and straw production were evaluated in plant cane and three ratoon crops. Soil samples were taken after evaluation of the third ratoon from seven layers (0–5, 5–10, 10–20, 20–40, 40–60, 60–80 and 80–100cm) to determine organic carbon, TC, particulate carbon (PC) and bulk density. Gypsum increased TC by 5.4 and 4.4Mgha–1 in the 0–100 and 40–100cm layers respectively. The PC pool in the 40–100cm layer was increased by 18.4%, whereas the carbon stock associated with mineral increased by 6.8% with gypsum application. Of the total increase in C stocks resulting from gypsum application, 80% occurred in the 40–100cm layer.

PH-dependent control of feldspar dissolution rate by altered surface layers

Relevant modeling of mass and energy fluxes involved in pedogenesis, sequestration of atmospheric CO2 or geochemical cycling of elements partly relies on kinetic rate laws of mineral dissolution obtained in the laboratory. Deriving an accurate and unified description of mineral dissolution has therefore become a prerequisite of crucial importance. However, the impact of amorphous silica-rich surface layers on the dissolution kinetics of silicate minerals remains poorly understood, and ignored in most reactive transport codes. In the present study, the dissolution of oriented cleavage surfaces and powders of labradorite feldspar was investigated as a function of pH and time at 80°C in batch reactors. Electron microscopy observations confirmed the formation of silica-rich surface layers on all samples. At pH=1.5, the dissolution rate of labradorite remained constant over time. In contrast, at pH=3, both the dissolution rates at the external layer/solution interface and the internal layer/mineral interface dramatically decreased over time. The dissolution rate at the external interface was hardly measurable after 4weeks of reaction, and decreased by an order of magnitude at the internal interface. In another set of experiments conducted in aqueous silica-rich solutions, the stabilization of silica-rich surface layers controlled the dissolution rate of labradorite at pH=3. The reduction of labradorite dissolution rate may result from a gradual modification of the textural properties of the amorphous surface layer at the fluid/mineral interface. The passivation of the main cleavage of labradorite feldspar was consistent with that observed on powders. Overall, our results demonstrate that the nature of the fluid/mineral interface to be considered in the rate limiting step of the process, as well as the properties of the interfacial layer (i.e. its chemical composition, structure and texture) to be taken into account for an accurate determination of the dissolution kinetics may depend on several parameters, such as pH or time. The dramatic impact of the stabilization of surface layers with increasing pH implies that the formation and the role of surface layers on dissolving feldspar minerals should be accounted for in the future.

An Initial Laboratory Prototype Experiment for Sequestration of Atmospheric CO2

AbstractAn initial phase of laboratory investigation has been completed in pursuit of a global-scale methodology for reduction of CO2 in ambient air through direct air capture (DAC). The methodology presented previously by Agee, Orton, and Rogers provides the background for this study. The laboratory prototype experiment presented has been designed to assess the potential for removing CO2 from ambient air by snow deposition. The approach consists of refrigeration to achieve the required CO2 deposition temperature of 135 K at 1 bar of pressure. The refrigerant of choice is liquid nitrogen (LN2) with cooling (77 K) at the top of a cylindrical 26.5-L Pyrex glass sequestration chamber. A highly conductive aluminum base with 14 instrumentation ports rests at the interface between the LN2 reservoir and the sequestration chamber. The cooling and mixing through Rayleigh–Taylor instability achieves uniform deposition temperature. Insulation to maintain the cooling process is provided to sustain CO2 depletion phase change at 135 K. The coldest temperature achieved in experimentation was 125 K. The required cooling period was 4.5 h, with an additional hour to achieve uniform chamber temperatures ≤ 135 K through top-down convective mixing. Experimental measurements showed a reduction of CO2 in the chamber air from initial values of ~500 ppmv down to 35 ppmv. Discussion is given to the issue of chamber CO2 frost versus CO2 snowflake formation, as well as the overall relevance of the experiment to DAC through refrigeration and storage in Antarctica to reduce atmospheric CO2.

Carbon sequestration in fly ash dumps: Comparative assessment of three plant association

The aim of the present study was to measure in-situ fly ash (FA) CO2 flux from naturally vegetated and non-vegetated sites of FA dumps for identifying potential plant species for carbon sequestration by using an automated soil CO2 flux system. The FA CO2 flux was found to be higher in vegetated site than non-vegetated site due to higher root density and respiration. The presence of organic carbon, microbial activity and root biomass are important indicators for sequestration of atmospheric CO2 in naturally vegetated site of FA dumps because of the fresh FA dumps are supposed to be initially free of organic carbon. Furthermore, in the naturally vegetated site, the FA CO2 efflux rates were least in Saccharum spontaneum (lower by 84.29%) and Prosopis juliflora (lower by 92.09%) association as compared to Typha latifolia association. Thus, the field results proved that S. spontaneum and P. juliflora associations are potentially suitable for sequestering atmospheric CO2 in the fresh FA deposited sites.

Assessment of Carbon Storage Potential and Area under Agroforestry Systems in Gujarat Plains by Co2fix Model and Remote Sensing Techniques

Agroforestry is a traditional and ancient land use practice, having deliberate integration of trees with crop and livestock components. In India, agroforestry practices are prevalent in different agro-ecological zones and occupy sizeable areas. These practices have great potential for climate change mitigation through sequestration of atmospheric CO 2 . Carbon sequestration potential was studied in four districts of Gujarat (Anand, Dahod, Patan and Junagarh), for which field survey was conducted to collect primary data on existing agroforestry systems. The extent of agroforestry area in these districts was estimated by sub-pixel classifier using medium resolution remote sensing data (RS-2/LISS III). By sub-pixel classifier, the highest area under agroforestry was estimated in Dahod (12.48%) followed by Junagarh district (10.95%) with an average of 9.12%. Sapota ( Manilkara zapota ) based agroforestry was also mapped in Junagarh district, which occupied an area of 1.13%. An accuracy of 87.2% was found by sub-pixel classifier in delineation of sapota-based agroforestry in the district. Dynamic CO2FIX model has been used to estimate total carbon (biomass + soils) and net carbon sequestered in existing agroforestry systems. Net carbon sequestered over a simulated period of 30 years in Anand, Dahod, Patan and Junagarh districts was found to be 2.70, 6.26, 1.61 and 1.50 Mg C ha -1 respectively. Total carbon stock in all four districts for baseline and simulated period of 30 years was estimated to be 2.907 and 3.251 million tonnes respectively. Thus, agroforestry systems in Gujarat have significant potential in carbon storage and trapping atmospheric CO 2 into biomass and soils. Hence, CO2FIX model in conjunction with remote sensing techniques can be successfully applied for estimating carbon sequestration potential of agroforestry systems in a district or a region.

Association of Soil Aggregation with the Distribution and Quality of Organic Carbon in Soil along an Elevation Gradient on Wuyi Mountain in China.

Forest soils play a critical role in the sequestration of atmospheric CO2 and subsequent attenuation of global warming. The nature and properties of organic matter in soils have an influence on the sequestration of carbon. In this study, soils were collected from representative forestlands, including a subtropical evergreen broad-leaved forest (EBF), a coniferous forest (CF), a subalpine dwarf forest (DF), and alpine meadow (AM) along an elevation gradient on Wuyi Mountain, which is located in a subtropical area of southeastern China. These soil samples were analyzed in the laboratory to examine the distribution and speciation of organic carbon (OC) within different size fractions of water-stable soil aggregates, and subsequently to determine effects on carbon sequestration. Soil aggregation rate increased with increasing elevation. Soil aggregation rate, rather than soil temperature, moisture or clay content, showed the strongest correlation with OC in bulk soil, indicating soil structure was the critical factor in carbon sequestration of Wuyi Mountain. The content of coarse particulate organic matter fraction, rather than the silt and clay particles, represented OC stock in bulk soil and different soil aggregate fractions. With increasing soil aggregation rate, more carbon was accumulated within the macroaggregates, particularly within the coarse particulate organic matter fraction (250–2000 μm), rather than within the microaggregates (53–250μm) or silt and clay particles (< 53μm). In consideration of the high instability of macroaggregates and the liability of SOC within them, further research is needed to verify whether highly-aggregated soils at higher altitudes are more likely to lose SOC under warmer conditions.

Formations of calcium carbonate minerals by bacteria and its multiple applications.

Biomineralization is a naturally occurring process in living organisms. In this review, we discuss microbially induced calcium carbonate precipitation (MICP) in detail. In the MICP process, urease plays a major role in urea hydrolysis by a wide variety of microorganisms capable of producing high levels of urease. We also elaborate on the different polymorphs and the role of calcium in the formation of calcite crystal structures using various calcium sources. Additionally, the environmental factors affecting the production of urease and carbonate precipitation are discussed. This MICP is a promising, eco-friendly alternative approach to conventional and current remediation technologies to solve environmental problems in multidisciplinary fields. Multiple applications of MICP such as removal of heavy metals and radionuclides, improve the quality of construction materials and sequestration of atmospheric CO2 are discussed. In addition, we discuss other applications such as removal of calcium ions, PCBs and use of filler in rubber and plastics and fluorescent particles in stationary ink and stationary markers. MICP technology has become an efficient aspect of multidisciplinary fields. This report not only highlights the major strengths of MICP, but also discusses the limitations to application of this technology on a commercial scale.

Unambiguous evidence of old soil carbon in grass biosilica particles

Abstract. Plant biosilica particles (phytoliths) contain small amounts of carbon called phytC. Based on the assumptions that phytC is of photosynthetic origin and a closed system, claims were recently made that phytoliths from several agriculturally important monocotyledonous species play a significant role in atmospheric CO2 sequestration. However, anomalous phytC radiocarbon (14C) dates suggested contributions from a non-photosynthetic source to phytC. Here we address this non-photosynthetic source hypothesis using comparative isotopic measurements (14C and δ13C) of phytC, plant tissues, atmospheric CO2, and soil organic matter. State-of-the-art methods assured phytolith purity, while sequential stepwise-combustion revealed complex chemical-thermal decomposability properties of phytC. Although photosynthesis is the main source of carbon in plant tissue, it was found that phytC is partially derived from soil carbon that can be several thousand years old. The fact that phytC is not uniquely constituted of photosynthetic C limits the usefulness of phytC either as a dating tool or as a significant sink of atmospheric CO2. It additionally calls for further experiments to investigate how SOM-derived C is accessible to roots and accumulates in plant biosilica, for a better understanding of the mechanistic processes underlying the silicon biomineralization process in higher plants.

Effects of eustatic sea-level change, ocean dynamics, and nutrient utilization on atmospheric &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and seawater composition over the last 130 000 years: a model study

Abstract. We have developed and employed an Earth system model to explore the forcings of atmospheric pCO2 change and the chemical and isotopic evolution of seawater over the last glacial cycle. Concentrations of dissolved phosphorus (DP), reactive nitrogen, molecular oxygen, dissolved inorganic carbon (DIC), total alkalinity (TA), 13C-DIC, and 14C-DIC were calculated for 24 ocean boxes. The bi-directional water fluxes between these model boxes were derived from a 3-D circulation field of the modern ocean (Opa 8.2, NEMO) and tuned such that tracer distributions calculated by the box model were consistent with observational data from the modern ocean. To model the last 130 kyr, we employed records of past changes in sea-level, ocean circulation, and dust deposition. According to the model, about half of the glacial pCO2 drawdown may be attributed to marine regressions. The glacial sea-level low-stands implied steepened ocean margins, a reduced burial of particulate organic carbon, phosphorus, and neritic carbonate at the margin seafloor, a decline in benthic denitrification, and enhanced weathering of emerged shelf sediments. In turn, low-stands led to a distinct rise in the standing stocks of DIC, TA, and nutrients in the global ocean, promoted the glacial sequestration of atmospheric CO2 in the ocean, and added 13C- and 14C-depleted DIC to the ocean as recorded in benthic foraminifera signals. The other half of the glacial drop in pCO2 was linked to inferred shoaling of Atlantic meridional overturning circulation and more efficient utilization of nutrients in the Southern Ocean. The diminished ventilation of deep water in the glacial Atlantic and Southern Ocean led to significant 14C depletions with respect to the atmosphere. According to our model, the deglacial rapid and stepwise rise in atmospheric pCO2 was induced by upwelling both in the Southern Ocean and subarctic North Pacific and promoted by a drop in nutrient utilization in the Southern Ocean. The deglacial sea-level rise led to a gradual decline in nutrient, DIC, and TA stocks, a slow change due to the large size and extended residence times of dissolved chemical species in the ocean. Thus, the rapid deglacial rise in pCO2 can be explained by fast changes in ocean dynamics and nutrient utilization whereas the gradual pCO2 rise over the Holocene may be linked to the slow drop in nutrient and TA stocks that continued to promote an ongoing CO2 transfer from the ocean into the atmosphere.

Potential and challenges of conservation agriculture in sequestration of atmospheric CO 2 for enhancing climate-resilience and improving productivity of soil of small landholder farms.

Abstract The projected climate change, caused by emissions from fossil fuel combustion and land use change, may adversely impact the agronomic yields and aggravate food insecurity of small landholder farms. About 500 million small landholder farms have depleted and degraded soils, while having low soil organic carbon (SOC) pools, low plant nutrient reserves, low plant-available water capacity and low agronomic yield, yet high vulnerability to changing and uncertain climate. Projected climate change may reduce rice yield by 10% for every 1°C increase in temperature, and total maize production may decline by 10% by 2050. Agronomic yield of wheat in South Asia may be adversely affected by increase in temperature during spring. Yield of other cereals (sorghum, millet) and root crops (cassava, yam) may be adversely affected by aggravation of other biotic stresses (smut, fungi, viruses, etc.). Thus, climate-resilience may be a key component of sustainable intensification of small landholder agriculture. It is in this context that conservation agriculture (CA) can be an important option. With fine-tuning for adaptation to site-specific conditions, CA has numerous benefits including erosion control, water conservation, SOC sequestration and increase in profitability and farm income. Further, CA can be implemented in synergism with other practices such as forestry and forest plantations (during early stages of tree establishment), and integrated crop-livestock (ley farming). In several farm operations, CA builds upon the traditional systems and indigenous technology. Widespread adoption of CA could sequester 1 Pg C/year globally, which could create another income stream for small landholders. Further, CA fits in with the '4 per Thousand' programme proposed at the COP-21 in Paris.