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Stabilizing climate requires reducing greenhouse gas (GHG) emissions and storing atmospheric carbon dioxide (CO2) in land or ocean systems. Soil management practices can reduce GHG emissions or sequester atmospheric CO2 into inorganic and organic forms. However, whether soil carbon strategies represent a viable and impactful climate mitigation pathway is uncertain. A specific question concerns the role that land-management practices and soil amendments can play in realizing California’s ambition for carbon neutrality by 2045. Here we examine the carbon flux impacts of soil conservation (i.e., compost, reduced tillage, cover crop) and enhanced silicate rock weathering (EW) practices at different areal extents of implementation in cropland, grassland, and savanna in California under two climate change cases. We show that with implementation areas of 15% or 50% of private cultivated land, grassland, and savanna in California, soil conservation practices alone can contribute 1.4 0.7 2.1 % ( − 1.8 − 0.9 − 2.7 Mt CO2eq y−1) and 4.6 2.3 6.9 % ( − 6.0 − 3.0 − 8.9 Mt CO2eq y−1) of the additional emissions reduction needed (beyond previous targets) to meet the 2045 net neutrality goal (−129.3 Mt CO2eq y−1), respectively, on an average annual basis, including climate uncertainty. Including EW in these scenarios increases the total contributions of management practices to 4.1 2.5 5.6 % ( − 5.2 − 3.2 − 7.3 Mt CO2eq y−1) and 13.5 8.2 18.6 % ( − 17.5 − 10.7 − 24.2 Mt CO2eq y−1), respectively, of this reduction. This highlights that the extent of implementation area is a major factor in determining benefits and that EW has the potential to make a real contribution to net reduction targets. Results are similar across climate cases, indicating that contemporary field data can be used to make future projections. With EW there remains mechanistic uncertainties, however, such as rock dissolution rate and environmental controls on weathering products, which require additional field research to improve understanding of the technological efficacy of this approach for California’s 2045 carbon neutrality goal.

Carbon burial patterns in lakes and their dynamic changes significantly impact terrestrial carbon sink fluxes and global carbon budgets. In this study, multi-indicator analysis of sediment core samples (P1, P2, and P3) from Pipahai Lake was conducted. Integrating the chronological sequences of 210Pb and 137Cs, we identified the historical changes and spatial characteristics of total organic carbon (TOC) and inorganic carbon (TIC) burial in Pipahai Lake since 1884. The results show that the TOC content was higher than that of the TIC. They exhibited an increasing trend with decreasing depth. Linear regression results indicated that the variation of TOC is less directly affected by precipitation (R = 0.39) and temperature (R = 0.58), while temperature may have a greater impact on TOC. From 1884 to 1995, nutrients were not the primary factor influencing changes in TOC. The synchronous variation in TIC and TOC contents reflects a higher contribution of external inputs to carbon burial in the Pipahai Lake basin. After 1996, nutrients may have begun to affect variations in TOC. The TOC primarily originates from distal aeolian transport or autochthonous sources, though human activity has played a role in its evolution. The TIC content is controlled by the TOC content and autochthonous sources. This study will contribute to the understanding of the carbon cycling dynamics and their influencing mechanisms in a high-altitude lake ecosystem. [ABSTRACT FROM AUTHOR]

Lakes are important carbon sinks in terrestrial ecosystems. Currently, most of lake carbon burial research in China only considers organic carbon burial and has neglected inorganic carbon burial, which will lead to an underestimation of the total carbon burial capacity of lakes. This situation is particularly significant in the humid eastern plain region. In order to comprehensively understand the carbon burial characteristics of lakes in the eastern plain and evaluate the contributions of organic and inorganic carbon burial to total carbon burial more reasonably. This research chooses Hongze Lake as study site, which is a representative lake in the eastern plain region. Based on the 210Pb-137Cs chronological sequence, combined with the C/N and δ13C characteristics in sediments, the carbon burial characteristics of Hongze Lake sediments in the past 60 years were explored by analyzing the spatiotemporal changes of organic and inorganic carbon content in typical rock cores (numbered HZH-12) and 11 other surface sediments. C/N and δ13C shows that endogenous organic carbon is the main source of organic carbon inHongze Lake . The significant synergistic changes in the accumulation rates of organic and inorganic carbon over the past 60 years (R2=0.76, p

Closed basin accounts for about one‐fifth of the global land area and is an important part of the global terrestrial carbon cycle. Due to its relatively close geographical environment and independent carbon cycling system, it is an ideal place to study regional carbon cycling. Here we present a carbon‐related proxy dataset for the Shiyang River Basin in the eastern part of the Hexi Corridor. The dataset collected carbon‐related indicator data for 997 sediment samples from 14 profiles, 92 surface sediment samples and 25 groundwater samples. It includes total nitrogen (TN), total organic carbon (TOC), inorganic carbon (IC), carbon‐nitrogen ratio (C/N), organic carbon isotopes (δ13Corg), carbonate carbon isotopes (δ13Ccarb), oxygen isotopes (δ18O) and other proxy indicator data, as well as profile and groundwater age data. These data will play an important role in studying organic carbon sinks, inorganic carbon sinks, carbon cycling processes and environmental changes in the closed basin. This dataset can be downloaded from https://doi.org/10.5281/zenodo.10252702. [ABSTRACT FROM AUTHOR]

The removal of atmospheric carbon dioxide (CO2) is now essential to meet net zero goals and limit the impacts of climate change. Enhanced weathering is a method of sequestering CO2 that involves the distribution of finely ground silicate rocks over agricultural land. The weathering of these silicate rocks releases cations into solution which can balance dissolved inorganic carbon, effectively removing CO2 from the atmosphere. Despite being a promising method of carbon dioxide removal (CDR), enhanced weathering has been limited by uncertainty surrounding the measurement of CO2 sequestration. This study compares current measurement approaches that focus on quantifying inorganic carbon and cations within the soil and leachate. Cation-based calculations of CDR were compared to inorganic carbon-based calculations of CDR and soil results were compared to leachate results. The recovery rate of cations in the soil fraction was also tested. Three different ground silicate minerals/rocks - basalt, olivine and wollastonite, were mixed with two different soils and were allowed to weather over 16 weeks in 320 pots with and without plants under different watering regimes and the application of an acidifying fertiliser. Soil and leachate samples were analysed for cations by ICP-OES and inorganic carbon by direct CO2 analysis after acidification and total alkalinity titration (in leachate only). The results indicate that the soil retains most enhanced weathering products through the cation exchange reactions. CDR estimated by cations is often greater than CDR estimated by inorganic carbon. Measurement approaches to estimate cations are susceptible to incomplete or improper accounting through the under-extraction of cations stored within the soil-exchangeable pool, the activity of non-carbonic acids and CO2 outgassing. Inorganic carbon-based measurements, including direct inorganic carbon and total alkalinity analysis, are also complicated by the potential for CO2 loss through carbonate precipitation and re-equilibration. Therefore, inorganic carbon-based approaches and cation-based approaches should be reconciled to validate the estimation of CDR. The inorganic carbon-based estimation of CDR in leachate should equal the cation-based estimation of CDR in leachate--which will be achieved after quantification or estimation of the natural mechanisms that affect each approach. These findings will support the development of accurate measurement processes for enhanced weathering. [ABSTRACT FROM AUTHOR]

In this paper, the generation of inorganic carbon (mainly HCO3−) in a karst system (soil-limestone system) under karst soil and non-karst soil conditions was investigated using two Zn2+ concentrations and water flow rates. The results showed that (1) the dynamic equilibrium state of the chemical weathering of limestone is altered by Zn2+, which is the primary cause of the change in HCO3− in soil-limestone systems; (2) ion exchange and adsorption are the primary characteristics of Zn2+ depletion under 1 mg/L ZnCl2 settings, whereas Zn2+ under 50 mg/L ZnCl2 conditions created two new solid phases (Zn5(OH)6(CO3)2, ZnCO3) in the soil-limestone system; (3) the dissolution rate of limestone increases with the water flow rate, which facilitates the dissolution process; (4) the notable difference in ion release between non-karst and karst soil conditions could potentially be attributed to variations in the mineral composition, specific surface area, and particle size of the two soil types; (5) the combination of SEM, XPS, FT-IR, and XRD microstructure observation methods reveals that when limestone is exposed to a high flow rate (1.23 mL/min) and a high concentration (50 mg/L) of ZnCl2, it experiences obvious dissolution and surface precipitation phenomena, as well as a significant change in HCO3− content. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology & Engineering Geology / Shuiwendizhi Gongchengdizhi is the property of Hydrogeology & Engineering Geology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study reevaluates the published total inorganic carbon (TIC) and total organic carbon (TOC) percentages of 695 seafloor sediment samples collected from the continental margins of the Black Sea, Sea of Marmara, Aegean Sea and Mediterranean Sea between 1984 and 1996. An inverse relationship is observed between the average TIC and TOC percentages in the four seas surrounding Türkiye. The explanation for this phenomenon is closely connected to the terrestrial, marine, climatic, and environmental factors of the continental margins from which the samples were collected. [ABSTRACT FROM AUTHOR]

Based on the high-precision isotopic composition and concentration of dissolved inorganic carbon (DIC) in the Bering Sea waters, their scopes and pathways are estimated in the Pacific sector of the Arctic Ocean. Although δ13С(DIC) and [DIC] are not classical conservative tracers, these parameters show the presence of both Atlantic and Pacific marine waters similar to the Bering Sea waters in the basin of the East Siberian Sea, which is a zone of active interaction of river and marine waters. The spatial distribution of Pacific and Atlantic and river waters is estimated using a three-component mixing model along two sections of the East Siberian Sea. The Pacific component propagates from east to west approximately to 160° E (probably, more westward) skirting Wrangel Island not only from the north but also probably from the south. The East Siberian Sea contains waters similar to the Bering Sea summer surface waters of the open sea, which are removed to the northern shelf by the circular Bering Sea Current, and to the upper intermediate waters, which can be involved in the zone of the northern sea shelf due to upwelling or active mixing. [ABSTRACT FROM AUTHOR]

In this paper, the generation of inorganic carbon (mainly HCO3−) in a karst system (soil-limestone system) under karst soil and non-karst soil conditions was investigated using two Zn2+ concentrations and water flow rates. The results showed that (1) the dynamic equilibrium state of the chemical weathering of limestone is altered by Zn2+, which is the primary cause of the change in HCO3− in soil-limestone systems; (2) ion exchange and adsorption are the primary characteristics of Zn2+ depletion under 1 mg/L ZnCl2 settings, whereas Zn2+ under 50 mg/L ZnCl2 conditions created two new solid phases (Zn5(OH)6(CO3)2, ZnCO3) in the soil-limestone system; (3) the dissolution rate of limestone increases with the water flow rate, which facilitates the dissolution process; (4) the notable difference in ion release between non-karst and karst soil conditions could potentially be attributed to variations in the mineral composition, specific surface area, and particle size of the two soil types; (5) the combination of SEM, XPS, FT-IR, and XRD microstructure observation methods reveals that when limestone is exposed to a high flow rate (1.23 mL/min) and a high concentration (50 mg/L) of ZnCl2, it experiences obvious dissolution and surface precipitation phenomena, as well as a significant change in HCO3− content.

Sustained time-series measurements are crucial to understand changes in oceanic carbonate chemistry. In the North Western Mediterranean Sea, the temporal evolution of the carbonate system is here investigated based on two 10-year time-series (between January 2010 and December 2019) of monthly carbonate parameters measurements at two sampling sites in the Ligurian Sea (ANTARES and DYFAMED). At seasonal timescale, the seawater partial pressure of CO2 (pCO2) within the mixed layer is mostly driven by temperature at both sites, and biological processes as stated by the observed relationships between total inorganic carbon (CT), nitrate and temperature. This study suggests also that mixing and water masses advection could play a role in modulating the CT content. At decadal timescale, significant changes in ocean chemistry are observed with increasing trends in CT (+3.2 ± 0.9 µmol.kg-1.a-1 - ANTARES; +1.6 ± 0.8 µmol.kg-1.a-1 - DYFAMED), associated with increasing pCO2 trends and decreasing trends in pH. The magnitude of the increasing trend in CT at DYFAMED is consistent with the increase in atmospheric pCO2 and the anthropogenic carbon transport of water originating from the Atlantic Ocean, while the higher trends observed at the ANTARES site could be related to the hydrological variability induced by the variability of the Northern Current. [ABSTRACT FROM AUTHOR]

[Objective] The effects of different mulching methods on the distribution of organic and inorganic carbon in soil aggregates on the Loess Plateau, and the mechanism under which soil aggregates sequester carbon under mulched conditions were determined in order to promote efficient management of dryland farm soil. [Methods] The study was conducted on a long-term positioning experiment beginning in 2012. Soil characteristics were studied from plots on which spring corn (“Xianyu 335”) was grown under three treatments: straw mulching (SM), film mulching (FM), and no mulching (CK). Carbon distribution and enzyme activities in aggregates of different particle sizes were determined by the wet sieve method. [Results] ① Organic carbon contents of aggregates of each particle size were significantly greater for SM than for CK (p2 mm in size, but significantly increased the reserves of aggregates 2 mm to 0.25 mm in size (p

Sustained time-series measurements are crucial to understand changes in oceanic carbonate chemistry. In the North Western Mediterranean Sea, the temporal evolution of the carbonate system is here investigated based on two 10-year time-series (between January 2010 and December 2019) of monthly carbonate parameters measurements at two sampling sites in the Ligurian Sea (ANTARES and DYFAMED). At seasonal timescale, the seawater partial pressure of CO2 (pCO2) within the mixed layer is mostly driven by temperature at both sites, and biological processes as stated by the observed relationships between total inorganic carbon (CT), nitrate and temperature. This study suggests also that mixing and water masses advection could play a role in modulating the CT content. At decadal timescale, significant changes in ocean chemistry are observed with increasing trends in CT (+3.2 ± 0.9 µmol.kg−1.a−1 – ANTARES; +1.6 ± 0.8 µmol.kg−1.a−1 – DYFAMED), associated with increasing pCO2 trends and decreasing trends in pH. The magnitude of the increasing trend in CT at DYFAMED is consistent with the increase in atmospheric pCO2 and the anthropogenic carbon transport of water originating from the Atlantic Ocean, while the higher trends observed at the ANTARES site could be related to the hydrological variability induced by the variability of the Northern Current.

Karstification forms tremendous karst carbon sinks in the Earth. Whether terrestrial higher plants can absorb and utilize bicarbonate, there is a key testimony that karst carbon sinks can be transformed into carbon sequestrations by terrestrial higher plants. The uptake and use of root-derived bicarbonate, photosynthesis, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase contents of Broussonetia papyrifera (Bp) and Morus alba L. (Ma) were measured. This study provides the most direct and primary evidence for the transformation using the bidirectional isotope tracer technique. The transformation may result from the synergism in the absorption and utilization of photosynthetic and nonphotosynthetic pathway, and simultaneously strengthen karst carbon sink and carbon sequestrations of plants, while it had no effect on photosynthetic CO2 assimilation in leaves. Differences in the transformation result in the discrepancies of Bp and Ma in the adaptation to karst environments. Karst-adaptable plants can more regulate the entire carbon cycle.

Copyright of Bulletin of Soil & Water Conservation is the property of Bulletin of Soil & Water Conservation Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The performance of microalgae-based wastewater treatment processes for ammonium-N (NH4+-N) removal depends on the maintenance of a favorable pH that is critical for minimizing nitrogen escape in the form of free ammonia (NH3) and preventing high-NH3 or extreme-pH stress. This study developed a CO2-inorganic carbon (CO2-IC) buffering system that automatically stabilized pH with the supply of a carbon source for efficient photosynthetic reclamation of NH4+-N by a euryhaline microalga Tetraselmis subcordiformis. The soluble (NaHCO3) and insoluble (CaCO3 and MgCO3) ICs were compared for this purpose. The pH was well controlled in the range of 6.5~8.5 in the CO2-IC system, which was suitable for the photosynthetic growth of T. subcordiformis. The NH4+-N (100 mg/L) was almost completely removed in three days, with the maximum removal rate of 60.13 mg N/L/day and minimal N escape of 19.65% obtained in the CO2-NaHCO3 system. The CO2-IC system also restricted the release of extracellular organic matter by preventing stress conditions. The CO2-NaHCO3 system enabled the highest "normal" starch production suitable for fermentation, while the CO2-CaCO3/MgCO3 system facilitated high-amylose starch accumulation that was conducive to producing bio-based materials and health-promoting ingredients. The proteins accumulated in T. subcordiformis were of good quality for animal feeds. [ABSTRACT FROM AUTHOR]

Using 25 years of data from the North-East Atlantic Ocean at the ESTOC site, we confirm the surface ocean is actively absorbing carbon emissions caused by human activities and undergoing ocean acidification. The carbon dioxide is also increasing in the subsurface and deepest waters. Seawater salinity normalized inorganic carbon (NCT), fugacity of CO2 (fCO2) and anthropogenic CO2 increase at a rate of 1.17 ± 0.07 µmol kg−1, 2.1 ± 0.1 µatm yr−1 and 1.06 ± 0.11 μmol kg−1 yr−1, respectively, while the ocean pHT fixed to the average temperature of 21°C, declines at a rate of 0.002 ± 0.0001 pH yr−1 in the first 100 m. These rates are 20% higher than values determined for the period 1995–2010. Over the 25 years, the average surface fCO2 increased by 52.5 µatm while the pHT declined by 0.051 pH units (~13% increase in acidity), like the observed seasonal signal. After 2020, seawater conditions are outside the range of surface fCO2 and pHT seasonal amplitude observed in the 1990s. It was also predicted by the year 2040, fCO2 seawater data will be smaller than atmospheric one and the area will be acting as a sink the full year around. Parameterizations of AT, CT, pHT and fCO2 using observations of water temperature, salinity and dissolved oxygen were determined for the ESTOC site with standard error of estimation of 6.5 µmol kg−1, 6.8 µmol kg−1, 0.010 pH and 9.6 µatm, respectively, and were applied to the North-East Atlantic Ocean. The observations and the parameterizations showed that the trends of the carbonate variables along the water column in the eastern subtropical ESTOC region are dominated by anthropogenically induced changes, observed in the whole water profile.

BackgroundExtraction of carbon from water is a crucial preprocessing step for measuring 14C in environmental waters using liquid scintillation spectrometry.PurposeThis study aims to explore the optimal technological conditions for extracting carbon from water using wet oxidation method.MethodsA wet oxidation system combining sodium persulfate and Fenton's reagent, along with phosphoric acid acidification and nitrogen bubbling, were employed for the wet oxidation carbon extraction experiments on two types of water samples with known (deionized water + sucrose) and unknown carbon components, each with a volume of 10 L. Simultaneously, carbon extraction experiments were conducted on the water samples having unknown carbon component, using a combination of wet oxidation and 185 nm ultraviolet (UV) oxidation so as to determine the optimal timing and sequence of reagent addition, as well as the optimized reagent dosage and ratio. Further experiments under optimized conditions were conducted to obtain more results for deep analysis.ResultsUnder the optimized conditions, after a 3-h reaction at 90 °C, the organic carbon extraction rate for the known carbon component (deionized water + sucrose) exceeds 96%. The total carbon extraction rate from the unknown carbon component water is (96.8±0.3)%, with an inorganic carbon extraction rate >98.5%, and an organic carbon extraction rate of (93.4±0.2)%, while the oxidation rate of tannic acid-type organic compounds is only (88±0.2)%. After the combination of wet oxidation and 185 nm UV oxidation, the total carbon extraction rate for the unknown carbon component increases to (98.3±0.5)%, with an inorganic carbon extraction rate ≥99% and an organic carbon extraction rate that can reach (95.6±1.4)%.ConclusionsResults of this study indicate that wet oxidation alone cannot represent the carbon recovery rate in actual water samples using typical organic compound carbon recovery rates. The combination of wet oxidation and 185 nm UV oxidation proves to be a more effective method for carbon extraction from water.

Stabilizing climate requires reducing greenhouse gas (GHG) emissions and storing atmospheric carbon dioxide (CO _2 ) in land or ocean systems. Soil management practices can reduce GHG emissions or sequester atmospheric CO _2 into inorganic and organic forms. However, whether soil carbon strategies represent a viable and impactful climate mitigation pathway is uncertain. A specific question concerns the role that land-management practices and soil amendments can play in realizing California’s ambition for carbon neutrality by 2045. Here we examine the carbon flux impacts of soil conservation (i.e., compost, reduced tillage, cover crop) and enhanced silicate rock weathering (EW) practices at different areal extents of implementation in cropland, grassland, and savanna in California under two climate change cases. We show that with implementation areas of 15% or 50% of private cultivated land, grassland, and savanna in California, soil conservation practices alone can contribute $1.4_{0.7}^{2.1}$ % ( $ - 1.8_{ - 0.9}^{ - 2.7}$ Mt CO _2 eq y ^−1 ) and $4.6_{2.3}^{6.9}$ % ( $ - 6.0_{ - 3.0}^{ - 8.9}$ Mt CO _2 eq y ^−1 ) of the additional emissions reduction needed (beyond previous targets) to meet the 2045 net neutrality goal (−129.3 Mt CO _2 eq y ^−1 ), respectively, on an average annual basis, including climate uncertainty. Including EW in these scenarios increases the total contributions of management practices to $4.1_{2.5}^{5.6}$ % ( $ - 5.2_{ - 3.2}^{ - 7.3}$ Mt CO _2 eq y ^−1 ) and $13.5_{8.2}^{18.6}$ % ( $ - 17.5_{ - 10.7}^{ - 24.2}$ Mt CO _2 eq y ^−1 ), respectively, of this reduction. This highlights that the extent of implementation area is a major factor in determining benefits and that EW has the potential to make a real contribution to net reduction targets. Results are similar across climate cases, indicating that contemporary field data can be used to make future projections. With EW there remains mechanistic uncertainties, however, such as rock dissolution rate and environmental controls on weathering products, which require additional field research to improve understanding of the technological efficacy of this approach for California’s 2045 carbon neutrality goal.

The oasis carbon pool in arid zones is an important part of the global carbon pool. There is a soil organic carbon (SOC)–soil–CO2–soil inorganic carbon (SIC) balanced system in the soil, which facilitates the change from soil organic carbon to soil inorganic carbon. A small change in the soil carbon pool can affect the overall global carbon balance, thus affecting the conversion of soil carbon in terrestrial ecosystems. In this study, the change from soil organic carbon to soil inorganic carbon (SIC) was obtained by measuring the δ13C values of SIC and CO2 in combination with stable carbon isotope techniques in cotton fields with different continuous cropping years, in the Alar Reclamation Area. Additionally, this was combined with redundancy analysis to reveal the effects of different physicochemical factors on the change amount. The results showed that the soil inorganic carbon content along the soil profile showed an increasing trend, while the soil organic carbon content was the opposite; the δ13C of SIC in the 0–20 and 60–80 cm soil layers were the highest in the 10a continuous cotton field soil, which were −22.24 and −21.86‰, respectively, and significantly different to other types (p < 0.05). The fixed carbon values in the barren, 5a, 10a, 20a, and 30a continuous cotton fields were 0.53, 0.17, 0.11, 0.13 and 0.33 g·kg−1, respectively; the corresponding amounts of CO2 fixed from soil respiration were 0.33, 0.11, 0.08, 0.05, and 0.25 g·kg−1; the amounts of CO2 from the atmosphere were 0.20, 0.06, 0.03, 0.02, and 0.09 g·kg−1; and the oxidative decomposition of CO2 by SOC were 0.17, 0.06, 0.04, 0.26, and 0.12 g·kg−1, respectively, indicating that the contribution of SOC was more in the barren field and 30a cotton field. Comparing the sources of fixed CO2, we found that the amount of fixed soil from barren fields and 30a was high from atmospheric CO2, while the contribution of SOC was low. Furthermore, the amount of fixed CO2 of 20a from SOC was high, and the atmospheric contribution was low. The main physicochemical factors that affecting the amount of soil SOC changed to SIC were soil water content, readily available carbon dioxide, and microbial biomass carbon. [ABSTRACT FROM AUTHOR]

Nitrite accumulation in hydrogen-based denitrification (HD) has been reported as a difficulty for achieving complete denitrification. Thauera sp. has been found as the dominant bacterial species in HD previously when using a plentiful amount of HCO3−. This present study was successful in isolating Pseudomonas sp., Dietzia sp., Pannonibacter sp., Halomonas sp., Bacillus sp., and Thauera sp. These isolated strains were selected for investigating the nitrogen removal performance under the plentiful HCO3− condition. Only Pseudomonas sp. and Thauera sp. were capable of removing NO2− where the specific NO2− removal rate of Thauera sp. (36.02 ± 5.66 mgN gVSS−1 day−1) was 9 times quicker than that of Pseudomonas sp. (3.94 ± 0.80 mgN gVSS−1 day−1). The Thauera sp. strain was then tested at different HCO3− amounts. As a result, Thauera sp. had no ability to function both NO3− and NO2− removals under HCO3− deficit condition. This study provided evidence on the role of Thauera sp. and the necessity of bicarbonate in the hydrogen-based denitrification process to enhance its efficiency and to simultaneously reduce the operational cost especially for hydrogen. [ABSTRACT FROM AUTHOR]

Autotrophic microorganisms, the pivotal carbon fixers, exhibit a broad distribution across diverse environments, playing critical roles in the process of carbon sequestration. However, insights into their distribution characteristics in aquifers, particularly in those petroleum-hydrocarbon-contaminated (PHC) aquifers that were known for rich in heterotrophs, have been limited. In the study, groundwater samples were collected from red clay aquifers in the storage tank leakage area of a PHC site, a prevalent aquifer type in southern China and other regions. Metagenomics combined with hydrochemical and inorganic carbon isotope analyses were employed to elucidate the presence of microbial carbon fixation and its driving forces. Results showed that there were hundreds of autotrophic microorganisms participating in distinct carbon fixation processes in the red clay PHC aquifers. Reductive tricarboxylic acid (rTCA) and dicarboxylate/4-hydroxybutyrate (DC/4HB), as well as 3-hydroxypropionate (3HP or/and 3-hydroxypropionate/4-hydroxybutyrate (3HP/4HB)) were the predominant carbon fixation pathways. The abundances of carbon fixation genes and autotrophic microorganisms were significantly and positively correlated with hydrocarbon concentrations and δ13C of dissolved inorganic carbon (δ13C-DIC) values. This finding indicated that the petroleum hydrocarbon significantly promoted the proliferation of carbon fixation microorganisms, leading to a substantial uptake of inorganic carbon. Therefore, we deduce that this process holds considerable potential for carbon sequestration in PHC-contaminated aquifers. [Display omitted] • Petroleum-hydrocarbon-contaminated red clay aquifers host carbon-fixing microbes. • Petroleum-hydrocarbons may enhance proliferation of carbon-fixing microorganisms. • Petroleum-hydrocarbon-contaminated aquifers hold carbon sequestration potential. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inorganic carbon promotes nitrate removal during H 2 -driven denitrification. • Inorganic carbon supplementation results into mixotrophic denitrification. • Inorganic carbon activates carbon fixation pathways for organic carbon conversion. • Inorganic carbon enhances enzymatic expressions and activities for nitrogen removal. H 2 -driven denitrification offers a promising alternative for treating low C/N wastewater amidst global nitrogen pollution, due to its advantages of high removal efficiency, low energy consumption, and independence from exogenous organic carbon source. While inorganic carbon assimilation is crucial for the growth and reproduction of autotrophic microorganisms, it remains uncertain whether the fixation of inorganic carbon could impact H 2 -driven denitrification. This work demonstrated that the supplement of inorganic carbon efficiently improved the efficiency of nitrate removal to 90.3%, compared to 78.0% in the control. Further analysis indicated that inorganic carbon supplementation shifted the microbial structure from autotrophic-dominated (e.g., Hydrogenophaga and Rhodococcus with abundance of 2.3% and 2.6%) to mixotrophic-dominated (e.g., Thauera and Microscillaceae sp. with abundance of 5.6% and 32.8%). Additionally, although H 2 boosted the carbon fixation via the reductive TCA cycle and Wood-Ljungdahl pathway, the Calvin-Benson cycle emerged as the predominant pathway, significantly boosted under inorganic carbon supplementation, along with the upregulation of critical enzyme expression including RuBisCo (EC 4.1.1.39), PGK (EC 2.7.2.3) and GAPDH (EC 1.2.1.12). Moreover, the expressions and activities of functional enzymes involved in nitrogen transformation, including nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR), as well as microbial electron transfer ability, were remarkably enhanced under sufficient inorganic carbon conditions. This work contributed to understanding the carbon metabolism mechanism in H 2 -driven denitrification, thereby facilitating the promotion of the efficient and low-carbon approach for nitrogen removal from wastewater. [ABSTRACT FROM AUTHOR]

Mature Fine Tailings (MFT) generated from oil sands processing represent a growing environmental issue, as settling of these tailings' emulsion can take decades, increasing the risk of the toxic material's leaching if left untreated. This study uses advanced wet air oxidation (WAO) and wet air peroxide oxidation (WAPO) to break down the MFT emulsions for faster settling. Three oxidation time intervals (5, 15, and 30 min) were investigated using compressed air and hydrogen peroxide in a pressurized vessel of 3.1–3.4 MPa internal pressure and at 200 °C temperature. The results showed that the WAO process was able to break the MFT emulsion, release trapped water, and recover residual bitumen. The WAPO process was much faster in breaking the emulsion; however, the presence of extra oxidants also resulted in the degradation of the residual bitumen. The 5 min oxidation time interval was found to be sufficient in breaking emulsions, separating water from soil particles, and recovering residual bitumen under the tested conditions. The oxidation process proved to be efficient by degrading all inorganic carbon, whereas 70% of the dissolved organic carbon in the recovered water after oxidation comprised only low molecular weight biodegradable hydrocarbons. Therefore, the WAO process was capable of breaking the MFT emulsions and allowing a faster settling of these tailings, with the added benefit of recovering residual bitumen. [ABSTRACT FROM AUTHOR]

Karstification forms tremendous karst carbon sinks in the Earth. Whether terrestrial higher plants can absorb and utilize bicarbonate, there is a key testimony that karst carbon sinks can be transformed into carbon sequestrations by terrestrial higher plants. The uptake and use of root-derived bicarbonate, photosynthesis, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase contents of Broussonetia papyrifera (Bp) and Morus alba L. (Ma) were measured. This study provides the most direct and primary evidence for the transformation using the bidirectional isotope tracer technique. The transformation may result from the synergism in the absorption and utilization of photosynthetic and nonphotosynthetic pathway, and simultaneously strengthen karst carbon sink and carbon sequestrations of plants, while it had no effect on photosynthetic CO2 assimilation in leaves. Differences in the transformation result in the discrepancies of Bp and Ma in the adaptation to karst environments. Karst-adaptable plants can more regulate the entire carbon cycle. [ABSTRACT FROM AUTHOR]

A comprehensive dataset of 138 surficial sediment samples retrieved from the shallow marine waters of six secondary compartments off the western coast of Victoria, Australia, is presented. Samples were collected between October 2018 and November 2020 at water depths ranging from four to 55 m using Shipek and Van Veen grabs. Sampling design targeted unconsolidated areas of the seafloor based on bathymetric and seafloor habitat data. Retrieved sediments were subsampled and subject to grain size analysis using a combination of dry sieving and laser diffraction methods, carbonate and organic matter content determination via Loss-on-Ignition, colour description using a Munsell chart, and roundness analysis using microscopic photography. This dataset, the most comprehensive surficial shallow water sedimentary record of the Otway Shelf, serves as a benchmark to understand sediment dynamics and conectivity along the coast, and can be used in environmental and engineering studies to support a range of management decisions.

The contents and isotope compositions of water and carbon, including total, reduced, and inorganic (carbonate) C, were studied in 170 My altered oceanic basalts from Ocean Drilling Program Hole 801C in the western Pacific Ocean. Reduced C contents of 0.12–0.29 wt% CO2 and $\delta ^{13}$C values of $-22.6$ to $-27.8‰$ occur throughout the basement section. High total C concentrations in the upper volcanic section (UVS), above 300 m sub-basement, are dominated by inorganic C, and concentrations of both decrease with depth, from 1.92 to 0.57 wt% CO2 and 1.76 wt% CO2 to 0.66 wt% CO2, respectively. The $\delta ^{13}$C of inorganic C in the UVS ($-$0.4 to ${+}1.5{‰}$) indicates precipitation of seawater dissolved inorganic carbon (DIC) through the intensive circulation of seawater. $\delta $D values of $-$59.8 to ${-}17.6{‰}$ in the UVS also result from seawater interaction. In contrast, total C contents in the lower volcanic section (LVS) are low (0.22–0.39 wt% CO2) and dominated by reduced C, resulting in negative $\delta ^{13}$C values for total C ($-$18.7 to ${-}23.5{‰}$). We propose that a proportion of this reduced C could have formed through abiotic reduction of magmatic CO2 at the ridge axis. The contents and $\delta ^{13}$C values of inorganic carbon in the LVS (0.05–0.09 wt% CO2 and $-$10.7 to ${-}9.5{‰}$, respectively) fall in the range characteristic of C in mid-ocean ridge basalt glasses, also suggesting a magmatic origin. $\delta $D values in the LVS (weighted average $= {-}69.3{‰}$) are consistent with magmatic water. Reduced C in the basalts may also have formed through microbial activity at low temperatures, as indicated by previous work showing negative $\delta ^{34}$S values in the basalts.Our results show: (1) that magmatic C can be stored in altered oceanic basalts both as reduced and inorganic C resulting from high-temperature processes at mid-ocean ridges; (2) that microbial activity may add reduced C to the basalts during low-temperature alteration on ridge flanks; and (3) that circulation of cold seawater in the uppermost few hundred meters of basement adds seawater DIC as carbonate to the basalts and filling fractures in the basement. We estimate the content of magmatic C stored in the altered basaltic crust to be 0.126 wt% CO2. Compared with previous estimates, this concentration probably represents an upper limit for magmatic C. This resultant magmatic C flux into the crust, ranging from $1.5\times 10^{12}$–$2\times 10^{12}$ molC${\cdot }$y$^{-1}$ is similar to the outgassing CO2 flux [${\sim }1.32\pm 0.8$–$2.0 \times 10^{12}$ molC${\cdot }$y$^{-1}$, Le Voyer et al., 2019 and Cartigny et al., 2018, respectively]. Further data are needed to better constrain the fraction of magmatic CO2 that does not escape the oceanic lithosphere but remains stored as reduced and inorganic carbon.

Carbonic anhydrase (CA) was considered to be an important component of carbon concentrating mechanism (CCM) of algae. It was an inducible enzyme. Environmental factors, especially dissolved inorganic carbon and pH, were known to affect CA activity. Effects of inorganic carbon (CO2 and HCO3−) and pH on CA activity of gametophytes of Saccharina japonica were evaluated in this study. Under high-CO2 condition (3% CO2), the activity of external CA (CAext) was significantly decreased (P

Herein, the effect of inorganic carbon (IC) limitation on the nitrogen removal performance of the single-stage reactor containing nitritation and anammox gel carriers was investigated. As a result of a continuous feeding test, the effluent ammonium concentration increased as the IC concentration decreased, indicating the deterioration of nitritation activity, not anammox. Furthermore, the sensitivity of IC to anammox and nitritation activity was investigated in anammox and nitritation reactors, respectively. Consequently, the relationship between the effluent IC concentration and nitritation rate was well described using the Michaelis–Menten equation. The apparent K m value of nitritation was calculated as 4.4 mg-C L−1. In anammox reactor, it was calculated as 1.7 mg-C L−1. These results revealed that the affinity of nitritation gel carriers to IC was lower than that of anammox, supporting that nitritation activity was easily deactivated by decrease in the IC concentration rather than anammox. Microbial community analysis revealed that Nitrosomonas europaea and Candidatus Jettenia asiatica were the dominant species of ammonium-oxidizing and anammox bacteria. [Display omitted] • The effect of IC on the nitrogen removal performance of SSR was investigated. • The nitrogen removal performance was decreased with decrease of IC. • The effects of IC on nitritation and anammox were determined. • The affinity to IC of nitritation gel carriers was lower than that of anammox. • Dominant species in gel carriers were Nitrosomonas europaea and Candidatus Jettenia asiatica. [ABSTRACT FROM AUTHOR]

The oasis carbon pool in arid zones is an important part of the global carbon pool. There is a soil organic carbon (SOC)–soil–CO2–soil inorganic carbon (SIC) balanced system in the soil, which facilitates the change from soil organic carbon to soil inorganic carbon. A small change in the soil carbon pool can affect the overall global carbon balance, thus affecting the conversion of soil carbon in terrestrial ecosystems. In this study, the change from soil organic carbon to soil inorganic carbon (SIC) was obtained by measuring the δ13C values of SIC and CO2 in combination with stable carbon isotope techniques in cotton fields with different continuous cropping years, in the Alar Reclamation Area. Additionally, this was combined with redundancy analysis to reveal the effects of different physicochemical factors on the change amount. The results showed that the soil inorganic carbon content along the soil profile showed an increasing trend, while the soil organic carbon content was the opposite; the δ13C of SIC in the 0–20 and 60–80 cm soil layers were the highest in the 10a continuous cotton field soil, which were −22.24 and −21.86‰, respectively, and significantly different to other types (p < 0.05). The fixed carbon values in the barren, 5a, 10a, 20a, and 30a continuous cotton fields were 0.53, 0.17, 0.11, 0.13 and 0.33 g·kg−1, respectively; the corresponding amounts of CO2 fixed from soil respiration were 0.33, 0.11, 0.08, 0.05, and 0.25 g·kg−1; the amounts of CO2 from the atmosphere were 0.20, 0.06, 0.03, 0.02, and 0.09 g·kg−1; and the oxidative decomposition of CO2 by SOC were 0.17, 0.06, 0.04, 0.26, and 0.12 g·kg−1, respectively, indicating that the contribution of SOC was more in the barren field and 30a cotton field. Comparing the sources of fixed CO2, we found that the amount of fixed soil from barren fields and 30a was high from atmospheric CO2, while the contribution of SOC was low. Furthermore, the amount of fixed CO2 of 20a from SOC was high, and the atmospheric contribution was low. The main physicochemical factors that affecting the amount of soil SOC changed to SIC were soil water content, readily available carbon dioxide, and microbial biomass carbon.

The Everglades Stormwater Treatment Areas (STAs) are a complex of large constructed wetlands that are an integral component of the State and Federal efforts to restore the Everglades ecosystem. The overall objective of this study was to determine the accumulation rates of macro‐elements including carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and associated secondary elements including calcium (Ca), magnesium (Mg), aluminum (Al), and iron (Fe) in two Everglades STAs over their periods of operation. The study was conducted in STA‐2 with parallel flow‐ways consisting of emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) and the Western flow‐way of STA‐3/4 with EAV and SAV cells operated in series. Elemental accumulation rates were determined in the unconsolidated surficial sediments (floc) and recently accreted soil (RAS) that have accumulated on top of the antecedent soil over the 14‐ and 10‐yr periods of operation for STA‐2 and STA‐3/4, respectively. Flow‐ways with SAV were more efficient than EAV in accreting mineral matter, resulting in increased bulk density and higher accumulation rates of elements. Average C accumulation in the floc and RAS of SAV flow‐ways was 320 g·m−2·yr−1 with approximately equal proportions of inorganic and organic C, while in the EAV flow‐ways accumulation rates of C ranged from 116 to 147 g·m−2·yr−1 with mostly organic C. Phosphorus accumulation rates were approximately 2–3 times higher in SAV than in EAV flow‐ways. Differences in accumulation of elements between SAV and EAV were largest for Ca with 17–42 times more Ca in SAV than EAV systems. This suggests that in the SAV systems, possible occlusion of macro‐elements and metals during CaCO3 precipitation facilitated accretion of material with high mineral content. In EAV, biomass turnover and associated biotic processes regulated organic matter accumulation rates. The spatial accumulation patterns of P, C, and N in the EAV areas of STA‐2 and STA‐3/4 were similar to those observed in the EAV areas of the natural wetlands in Water Conservation Areas, suggesting that constructed wetland systems function similarly to natural wetlands dominated by EAV areas in retaining and storing macro‐ and secondary elements. [ABSTRACT FROM AUTHOR]

Abstract The Everglades Stormwater Treatment Areas (STAs) are a complex of large constructed wetlands that are an integral component of the State and Federal efforts to restore the Everglades ecosystem. The overall objective of this study was to determine the accumulation rates of macro‐elements including carbon (C), nitrogen (N), phosphorus (P), sulfur (S), and associated secondary elements including calcium (Ca), magnesium (Mg), aluminum (Al), and iron (Fe) in two Everglades STAs over their periods of operation. The study was conducted in STA‐2 with parallel flow‐ways consisting of emergent aquatic vegetation (EAV) and submerged aquatic vegetation (SAV) and the Western flow‐way of STA‐3/4 with EAV and SAV cells operated in series. Elemental accumulation rates were determined in the unconsolidated surficial sediments (floc) and recently accreted soil (RAS) that have accumulated on top of the antecedent soil over the 14‐ and 10‐yr periods of operation for STA‐2 and STA‐3/4, respectively. Flow‐ways with SAV were more efficient than EAV in accreting mineral matter, resulting in increased bulk density and higher accumulation rates of elements. Average C accumulation in the floc and RAS of SAV flow‐ways was 320 g·m−2·yr−1 with approximately equal proportions of inorganic and organic C, while in the EAV flow‐ways accumulation rates of C ranged from 116 to 147 g·m−2·yr−1 with mostly organic C. Phosphorus accumulation rates were approximately 2–3 times higher in SAV than in EAV flow‐ways. Differences in accumulation of elements between SAV and EAV were largest for Ca with 17–42 times more Ca in SAV than EAV systems. This suggests that in the SAV systems, possible occlusion of macro‐elements and metals during CaCO3 precipitation facilitated accretion of material with high mineral content. In EAV, biomass turnover and associated biotic processes regulated organic matter accumulation rates. The spatial accumulation patterns of P, C, and N in the EAV areas of STA‐2 and STA‐3/4 were similar to those observed in the EAV areas of the natural wetlands in Water Conservation Areas, suggesting that constructed wetland systems function similarly to natural wetlands dominated by EAV areas in retaining and storing macro‐ and secondary elements.

Lake carbon burial is of vital significance in global carbon cycle and carbon budget, particularly in the large deepwater lakes. However, carbon burial in large deepwater lakes is hard to estimate due to the difficulty in obtaining high spatial-resolution samples. In this study, we investigated distributions of total organic carbon (TOC) and inorganic carbon (TIC), two main carbon components in lake sediments, based on dozens of surficial sedimentary samples (n = 26) covering whole Lake Qinghai, the largest saline lake in China. The results showed that the TOC content, with a range of 1.4–4.8%, was significantly higher in the lake area near the northern lakeshore where human activities are concentrated and lower in the lake areas near the Buha River mouth and the eastern lake area. In contrast, the TIC content, ranging from 1.5 to 3.8%, increased from the northwestern and southeastern lake areas toward the lake center, and mainly depended on hydro-chemical and hydraulic characteristics. The inorganic carbon burial (47.77 ± 19.73 Gg C yr−1) was approximately equal to organic carbon burial (47.50 ± 22.68 Gg C yr−1) and accounted for about 50% of the total carbon burial (95.27 ± 37.74 Gg C yr−1), suggesting that saline lakes constitute a large inorganic carbon pool in addition to an organic carbon pool. Because of saline water body type in arid and semiarid regions and alpine Qinghai–Tibet Plateau, lakes in these regions have huge inorganic carbon burial potential and important contributions to the global carbon budget.

This paper investigates a mathematical model of competition between two species for inorganic carbon and light in a well-mixed water column. The population growth of the species depends on the consumption of two substitutable forms of inorganic carbon, "CO2" (dissolved CO2 and carbonic acid) and "CARB" (bicarbonate and carbonate ions), which are stored internally. Besides, uptake rates also includes self-shading by the phytoplankton population, that is, an increase in population density will reduce light available for photosynthesis, and thereby reducing further carbon assimilation and population growth. We also incorporate the fact that carbon is lost by respiration, and the respiration rate is assumed to be proportional to the size of the transient carbon pool. Then we study the extinction and persistence of a single-species system. Finally, we show that coexistence of the two-species system is possible, depending on parameter values, and both persistence of one population.

The seasonal variability of the carbonate system in the eastern Mediterranean Sea (EMed) was investigated based on discrete total alkalinity (AT), total dissolved inorganic carbon (CT), and pH measurements collected during three cruises around Crete between June 2018 and March 2019. This study presents a detailed description of this new carbonate chemistry dataset in the eastern Mediterranean Sea. We show that the North Western Levantine Basin (NWLB) is unique in terms of range of AT variation vs. CT variation in the upper water column over an annual cycle. The reasons for this singularity of the NWLB can be explained by the interplay between strong evaporation and the concomitant consumption of CT by autotrophic processes. The high range of AT variations, combined to temperature changes, has a strong impact on the variability of the seawater pCO2 (pCO2SW). Based on Argo float data, an entire annual cycle for pCO2SW in the NWLB has been reconstructed in order to estimate the temporal sequence of the potential “source” and “sink” of atmospheric CO2. By combining this dataset with previous observations in the NWLB, this study shows a significant ocean acidification and a decrease in the oceanic surface pHT25 of −0.0024 ± 0.0004 pHT25 units.a–1. The changes in the carbonate system are driven by the increase of atmospheric CO2 but also by unexplained temporal changes in the surface AT content. If we consider that the EMed will, in the future, encounter longer, more intense and warmer summer seasons, this study proposes some perspectives on the carbonate system functioning of the “future” EMed.

Stemflow can be an important pathway for the drainage of precipitation and related solutes through tree canopies to forest soils. As stemflow must drain along bark surfaces, the effects of bark structure on stemflow chemical composition is merited. This study examines the relationship between stemflow chemistry and bark surface structure for six species of varying bark morphology (four deciduous broadleaf trees and two evergreen coniferous trees) at a montane and an urban site in Japan. Stemflow from smooth-barked species contained greater concentrations of solutes that appear to be rinsed from the stem surface (i.e., sea salt aerosols); while, rougher-barked tree species contained greater or less concentrations of solutes that appear to be leached (e.g., Ca2+) or taken-up (e.g., inorganic N) by the bark, respectively. Site-specific atmospheric environments also influenced thee bark-stemflow chemistry relationships—where the greater elemental deposition in the urban plot generally resulted in greater stemflow chemistry than observed in the lower-deposition montane plot. Our results therefore suggest that the dynamics of dry deposition wash-off by stemflow, and the exchange of dissolved solutes between stemflow and the bark surface, are influenced by the surface structure of the bark and the site’s atmospheric environment. Therefore, the interactions between bark surface structure and its surrounding atmospheric environment are important factors in the stemflow-related elemental cycling between the tree and precipitation.

Continental shelf sediments are recognized as long-term stores of globally significant quantities of carbon (C) and potentially provide an important, yet largely overlooked climate regulation service via the Earth’s C cycle. Current understanding of the spatial distribution of sedimentary C across continental shelves remains poor, inhibiting the targeted management and potential inclusion of these globally significant C stores into national C budgets. Further understanding of the spatial heterogeneity of continental shelf sediments and associated C provides a foundation to quantify the organic carbon (OC) stock and better understand the role that marine sediments play in regulating the global climate and the potential for CO2 to be released through anthropogenic disturbance of these C stores. Utilizing a spectrum of available marine data, we have created bespoke sediment maps that quantify the surficial (top 10 cm) OC stock and highlight significant spatial heterogeneity in the distribution of sediments and their associated C content across the United Kingdom’s Exclusive Economic Zone (EEZ). The surficial sediments within the UK EEZ are estimated to store 524 ± 68 Mt of organic carbon (OC) and 2,582 ± 168 Mt of inorganic carbon (IC). The spatial mapping of this C highlights well-defined OC accumulation hotspots in fjords, estuaries and coastal muds, while large accumulations of IC are found in the tidally swept areas around Orkney, Shetland and the South West of England. Within the well-defined OC hotspots, muddy sediments store the greatest quantity of OC; the muds offer potentially valuable opportunities for targeted future management and protection of sedimentary C stores within the UK EEZ. In the future, if areas of the seafloor were to be managed to include the protection of these valuable sedimentary C resources, we recommend an initial focus on hotspots of high sedimentary OC density.

Summary: Cell size influences the rate at which phytoplankton assimilate dissolved inorganic carbon (DIC), but it is unclear whether volume‐specific carbon uptake should be greater in smaller or larger cells. On the one hand, Fick's Law predicts smaller cells to have a superior diffusive CO2 supply. On the other, larger cells may have greater scope to invest metabolic energy to upregulate active transport per unit area through CO2‐concentrating mechanisms (CCMs).Previous studies have focused on among‐species comparisons, which complicates disentangling the role of cell size from other covarying traits. In this study, we investigated the DIC assimilation of the green alga Dunaliella tertiolecta after using artificial selection to evolve a 9.3‐fold difference in cell volume. We compared CO2 affinity, external carbonic anhydrase (CAext), isotopic signatures (δ13C) and growth among size‐selected lineages.Evolving cells to larger sizes led to an upregulation of CCMs that improved the DIC uptake of this species, with higher CO2 affinity, higher CAext and higher δ13C. Larger cells also achieved faster growth and higher maximum biovolume densities.We showed that evolutionary shifts in cell size can alter the efficiency of DIC uptake systems to influence the fitness of a phytoplankton species. [ABSTRACT FROM AUTHOR]

This study illustrated the growth of Scenedesmus obliquus and recycle of nutrients in wastewater combined with inorganic carbon under autotrophic conditions. Scenedesmus obliquus was cultivated under different conditions by adding sodium carbonate (Na2CO3) at 15–40 mg l−1 separately in wastewater containing high nitrogen and phosphorus content. The growth characteristics of S. obliquus, pH and dissolved inorganic carbon (DIC) changes of microalgae liquid, the recycle rate of ammonia and phosphorus and lipid content were determined. The changes of pH and DIC showed that S. obliquus could use Na2CO3 to grow, with lipid contents of 18–25%. Among all Na2CO3 concentrations, 20 mg l−1 was the optimum, of which S. obliquus had the highest NH3-N recycle of 52% and PO43–P recycle of 67%. By the 14th day, its biomass production also reaches the maximum of 0.21 g l−1. However, inorganic carbon fixation rate was inversely proportional to its concentration. Moreover, the biomass was in positive correlation with the Na2CO3 concentration except 20 mg l−1, which provided a possibility that S. obliquus could be acclimatized to adjust to high concentrations of inorganic carbon to promote biomass accumulation and recycle of nutrients.

Landscapes of the northern part of the Bolshoi Paipudynskii Ridge (the Polar Urals) served as a key site to study the taxonomic diversity of soils on calcareous rocks as related to both bioclimatic and geogenic (relief, thickness of eluvial and colluvial derivatives of calcareous rocks) factors. Soils of the postlithogenic trunk of the new Russian soil classification system are developed under different plant communities. They are classified within several soil orders: cryometamorphic soils (Mollic Calcaric Stagnosols), lithozems (Folic Mollic Calcaric Leptosols), organo-accumulative soils (Molic Leptic Calcaric Stagnosols), and gley soils (Folic Calcaric Gleysols). These soils compose either small individual areas, or occur in soil associations. The mass of carbon and nitrogen in the aboveground phytomass ranges within 40–49 and 0.9–2.3%, respectively. The storage of aboveground phytomass (fresh weight) varies from 20 to 1600 g/m2. In each soil profile, the surface horizons have a maximum content of organic carbon and nitrogen (up to 40 and 2.5%, respectively). The Corg and Norg patterns in soils depend on the productivity of plant communities, the composition of falloff, and the conditions for its decomposition. In all soil profiles, the inorganic carbon content (Cinorg) increases down the soil profile reaching 12%. The mineral nitrogen content does not exceed 1%. The contents of N- and N- have their maximums reaching 140 and 30 mg/kg, respectively, in the surface soil horizons. [ABSTRACT FROM AUTHOR]

Global change includes invasion by exotic (nonnative) plant species and altered precipitation patterns, and these factors may affect terrestrial carbon (C) storage. We measured soil C changes in experimental mixtures of all exotic or all native grassland plant species under two levels of summer drought stress (0 and +128 mm). After 8 yr, soils were sampled in 10‐cm increments to 100‐cm depth to determine if soil C differed among treatments in deeper soils. Total soil C (organic + inorganic) content was significantly higher under native than exotic plantings, and differences increased with depth. Surprisingly, differences after 8 yr in C were due to carbonate and not organic C fractions, where carbonate was ~250 g C/m2 lower to 1‐m soil depth under exotic than native plantings. Our results indicate that soil carbonate is an active pool and can respond to differences in plant species traits over timescales of years. Significant losses of inorganic C might be avoided by conserving native grasslands in subhumid ecosystems. [ABSTRACT FROM AUTHOR]

Summary: In response to high CO2 environmental variability, green algae, such as Chlamydomonas reinhardtii, have evolved multiple physiological states dictated by external CO2 concentration. Genetic and physiological studies demonstrated that at least three CO2 physiological states, a high CO2 (0.5–5% CO2), a low CO2 (0.03–0.4% CO2) and a very low CO2 (< 0.02% CO2) state, exist in Chlamydomonas. To acclimate in the low and very low CO2 states, Chlamydomonas induces a sophisticated strategy known as a CO2‐concentrating mechanism (CCM) that enables proliferation and survival in these unfavorable CO2 environments. Active uptake of Ci from the environment is a fundamental aspect in the Chlamydomonas CCM, and consists of CO2 and HCO3– uptake systems that play distinct roles in low and very low CO2 acclimation states. LCI1, a putative plasma membrane Ci transporter, has been linked through conditional overexpression to active Ci uptake. However, both the role of LCI1 in various CO2 acclimation states and the species of Ci, HCO3– or CO2, that LCI1 transports remain obscure. Here we report the impact of an LCI1 loss‐of‐function mutant on growth and photosynthesis in different genetic backgrounds at multiple pH values. These studies show that LCI1 appears to be associated with active CO2 uptake in low CO2, especially above air‐level CO2, and that any LCI1 role in very low CO2 is minimal. Significance Statement: LCI1 is a novel plasma membrane Ci transporter involved in active Ci uptake to support the Chlamydomonas CO2‐concentrating mechanism (CCM), although its precise function is unknown. By analyzing Ci‐dependent O2 evolution responses of an LCI1 loss‐of‐function mutant in different genetic backgrounds and pH values, we reveal a specific role for LCI1 in active CO2 uptake in the low CO2 range, especially above air‐level CO2. [ABSTRACT FROM AUTHOR]

Summary: In response to high CO2 environmental variability, green algae, such as Chlamydomonas reinhardtii, have evolved multiple physiological states dictated by external CO2 concentration. Genetic and physiological studies demonstrated that at least three CO2 physiological states, a high CO2 (0.5–5% CO2), a low CO2 (0.03–0.4% CO2) and a very low CO2 (< 0.02% CO2) state, exist in Chlamydomonas. To acclimate in the low and very low CO2 states, Chlamydomonas induces a sophisticated strategy known as a CO2‐concentrating mechanism (CCM) that enables proliferation and survival in these unfavorable CO2 environments. Active uptake of Ci from the environment is a fundamental aspect in the Chlamydomonas CCM, and consists of CO2 and HCO3– uptake systems that play distinct roles in low and very low CO2 acclimation states. LCI1, a putative plasma membrane Ci transporter, has been linked through conditional overexpression to active Ci uptake. However, both the role of LCI1 in various CO2 acclimation states and the species of Ci, HCO3– or CO2, that LCI1 transports remain obscure. Here we report the impact of an LCI1 loss‐of‐function mutant on growth and photosynthesis in different genetic backgrounds at multiple pH values. These studies show that LCI1 appears to be associated with active CO2 uptake in low CO2, especially above air‐level CO2, and that any LCI1 role in very low CO2 is minimal. Significance Statement: LCI1 is a novel plasma membrane Ci transporter involved in active Ci uptake to support the Chlamydomonas CO2‐concentrating mechanism (CCM), although its precise function is unknown. By analyzing Ci‐dependent O2 evolution responses of an LCI1 loss‐of‐function mutant in different genetic backgrounds and pH values, we reveal a specific role for LCI1 in active CO2 uptake in the low CO2 range, especially above air‐level CO2. [ABSTRACT FROM AUTHOR]

This study extends the 1991-1995 records of marine dissolved organic carbon (DOC) concentrations and Δ14C values at hydrographic Station M (34°50′N, 123°00′W) with new measurements from a frozen (-20 °C) archive of samples collected between April 1998 and October 2004. The magnitudes and synchronicity of major Δ14C anomalies throughout the time-series imply transport of DOC from the surface ocean to depths of at least 450 m on the timescale of months. Keeling plots of all measurements at Station M predict a continuum of possible background DOC compositions containing at least 21 μM of -1000‰ (i.e., ≥57,000 14C years) DOC, but are more consistent with mean deep DOC (38 μM, -549‰; i.e., ∼6,400 14C years). These results and coral records of surface dissolved inorganic carbon (DIC) Δ14C were used to estimate pre-bomb DOC Δ14C depth profiles. The combined results indicate that bomb-14C has penetrated the DOC pool to depths of ≥450 m, though the signal at that depth is obscured by short-term variability.