Inorganic Carbon Concentrations Research Articles

The impact of the South-East Madagascar Bloom on the oceanic CO<sub>2</sub> sink

Abstract. We described new sea surface CO2 observations in the south-western Indian Ocean obtained in January 2020 when a strong bloom event occurred south-east of Madagascar and extended eastward in the oligotrophic Indian Ocean subtropical domain. Compared to previous years (1991–2019) we observed very low fCO2 and dissolved inorganic carbon concentrations (CT) in austral summer 2020, indicative of a biologically driven process. In the bloom, the anomaly of fCO2 and CT reached respectively −33 µatm and −42 µmol kg−1, whereas no change is observed for alkalinity (AT). In January 2020 we estimated a local maximum of air–sea CO2 flux at 27∘ S of −6.9 mmol m−2 d−1 (ocean sink) and −4.3 mmol m−2 d−1 when averaging the flux in the band 26–30∘ S. In the domain 25–30∘ S, 50–60∘ E we estimated that the bloom led to a regional carbon uptake of about −1 TgC per month in January 2020, whereas this region was previously recognized as an ocean CO2 source or near equilibrium during this season. Using a neural network approach that reconstructs the monthly fCO2 fields, we estimated that when the bloom was at peak in December 2019 the CO2 sink reached −3.1 (±1.0) mmol m−2 d−1 in the band 25–30∘ S; i.e. the model captured the impact of the bloom. Integrated in the domain restricted to 25–30∘ S, 50–60∘ E, the region was a CO2 sink in December 2019 of −0.8 TgC per month compared to a CO2 source of +0.12 (±0.10) TgC per month in December when averaged over the period 1996–2018. Consequently in 2019 this region was a stronger CO2 annual sink of −8.8 TgC yr−1 compared to −7.0 (±0.5) TgC yr−1 averaged over 1996–2018. In austral summer 2019–2020, the bloom was likely controlled by a relatively deep mixed-layer depth during the preceding winter (July–September 2019) that would supply macro- and/or micro-nutrients such as iron to the surface layer to promote the bloom that started in November 2019 in two large rings in the Madagascar Basin. Based on measurements in January 2020, we observed relatively high N2 fixation rates (up to 18 nmol N L−1 d−1), suggesting that diazotrophs could play a role in the bloom in the nutrient-depleted waters. The bloom event in austral summer 2020, along with the new carbonate system observations, represents a benchmark case for complex biogeochemical model sensitivity studies (including the N2 fixation process and iron supplies) for a better understanding of the origin and termination of this still “mysterious” sporadic bloom and its impact on ocean carbon uptake in the future.

Transmitted Cross-Polarized Light Detection of Particulate Inorganic Carbon Concentrations and Fluxes in the Ocean Water Column: Ships to ARGO Floats

Particulate inorganic carbon (PIC) plays a major role in the ocean carbon cycle impacting pH, dissolved inorganic carbon, and alkalinity, as well as particulate organic carbon (POC) export and transfer efficiency to the deep sea. Remote sensing retrievals of PIC in surface waters span two decades, yet knowledge of PIC concentration variability in the water column is temporally and spatially limited due to a reliance on ship sampling. To overcome the space–time gap in observations, we have developed optical sensors for PIC concentration and flux that exploit the high mineral birefringence of CaCO3 minerals, and thus enable real-time data when deployed operationally from ship CTDs and ARGO-style Carbon Flux Explorer floats. For PIC concentrations, we describe a fast (10 Hz) digital low-power (∼0.5 W) sensor that utilizes cross-polarized transmitted light to detect the photon yield from suspended birefringent particles in the water column. This sensor has been CTD-deployed to depths as great as 6,000 m and cross-calibrated against particulates sampled by large volume in situ filtration and CTD/rosettes. We report data from the September–November 2018 GEOTRACES GP15 meridional transect from the Aleutian Islands to Tahiti along 152°W where we validated two prototype sensors deployed on separate CTD systems surface to bottom at 39 stations, many of which were taken in nearly particle-free waters. We compare sensor results with major particle phase composition (particularly PIC and particulate aluminum) from simultaneously collected size-fractionated particulate samples collected by large volume in situ filtration. We also report results from the June 2017 California Current Ecosystem-Long Term Ecological Research (CCE-LTER) process study in California coastal waters where high PIC levels were found. We demonstrate that the PIC concentration sensor can detect PIC concentration variability from 0.01 to >1 μM in the water column (except in nepheloid layers) and outline engineering needs and progress on its integration with the Carbon Flux Explorer, an autonomous float.

Identification of the sources and influencing factors of the spatial variation of heavy metals in surface sediments along the northern Jiangsu coast

Determining the sources and factors influencing the spatial variation of heavy metals in the surface sediments of tidal flats is important for controlling and reducing heavy metal pollution. We used principal component analysis and partial least square regression to analyse the distribution characteristics, sources, and factors influencing the spatial variation of nine heavy metals (As, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn) in the surface sediments of tidal flats along four sites located on the northern Jiangsu coast. Our results indicate that the northern three sampling areas had a high heavy metal content, whereas the southern sampling area had a low heavy metal content. The heavy metals Mn and Pb are related to both natural and anthropogenic sources, whereas V and Cr are primarily derivatives of human activities, and As, Co, Cu, Ni, and Zn are primarily a result of natural processes. The spatial variation of Mn and Pb was primarily affected by the total inorganic carbon and clay content (positive affect) as well as the sand and silt content (negative affect). The spatial variation of V and Cr was primarily related to silt, clay, and total phosphorus content (positive influence) as well as sand (negative influence). In addition, the spatial variation of As, Co, Cu, Ni, and Zn was primarily influenced by the total organic carbon and clay content (positive effect) as well as sand and pH (negative effect). The grain size of sediments plays an important role in the spatial variation of heavy metals in the surface sediments of tidal flats, with fine-grained clay materials being related to the enrichment of heavy metals. The results of our study are important for the control and reduction of heavy metal pollution in coastal sediments, protecting both the ecological environment and human health.

Provenance of Inorganic Carbon Sinks in Closed Basins

AbstractMuch dissolved inorganic carbon (DIC) may exist in lacustrine carbonates in the terminal lakes of closed basins in arid areas, and inorganic carbon sinks in arid regions are an important hypothesis of global carbon cycle research in recent years. Previous studies have made significant progress in estimating the inorganic carbon content. However, the source of inorganic carbon sinks remains unclear. Here, we choose four typical arid closed basins in North China to investigate the provenance of inorganic carbon sinks. The results show that CO2 absorbed by saline‐alkaline soil is the main source of groundwater DIC in the study area, with a contribution rate of approximately 50%. Forty‐three groundwater radiocarbon ages from arid closed basins indicate that the DIC in groundwater is transported along the direction of water flow and deposited in terminal lakes, forming inorganic carbon sinks. Our study suggests that the total inorganic carbon contents of Zhuye Lake, Yanchi Lake, Huahai Lake, and Qinghai Lake in the Holocene are 0.318 Pg, 0.003 Pg, 0.160 Pg, and 3.289 Pg, respectively. The results demonstrate that inorganic carbon sinks are much larger than lake organic carbon storage, thereby serving as an important carbon cycle factor in arid regions.

Synchronic changes of lake organic and inorganic carbon burial in response to catchment development over the past century: A case study of Shilin Karst area

有机碳和无机碳的流域输出是湖泊碳埋藏的重要驱动因子, 而喀斯特地区无机碳循环具有反应迅速且对人类活动影响敏感的特点. 在流域开发持续增强的背景下, 喀斯特地区湖泊有机碳和无机碳的来源、含量与埋藏通量可能会出现同步变化的协同模式. 本文以云南省石林喀斯特地区流域土地利用类型不同的两个中型湖泊(长湖、月湖)开展对比分析, 通过对沉积物钻孔的土壤侵蚀强度(磁化率)、流域外源输入(C∶N比值)、水动力(粒度)、营养盐(总氮、总磷)、藻类生产力(叶绿素色素)等代用指标的分析, 结合监测数据和历史资料重建了两个湖泊环境变化的近百年历史, 并定量识别了有机碳和无机碳埋藏响应流域开发的变化特征与协同模式. 沉积物磁化率和C∶N比值结果揭示了流域地表侵蚀和外源输入的阶段性特征, 同时总氮和总磷含量记录了长湖和月湖营养水平上升的长期模式. 在流域森林覆被较高(33.43%)的长湖中, 全岩和有机质C∶N比值分别与磁化率信号呈显著正相关(r=0.95和0.89, P＜0.001), 且与无机碳和有机碳含量呈显著负相关(r=-0.94, P＜0.001和r=-0.52, P=0.01), 反映了森林植被退化时流域碳输出的减少对沉积物碳含量的影响. 而在流域耕地覆被为主(60.98%)的月湖中, 全岩和有机质C∶N比值与磁化率信号呈显著负相关(r=-0.54, P＜0.01和r=-0.67, P＜0.001), 且全岩C∶N比值与无机碳含量(P=0.15)无显著关系, 反映了耕作强度的增加可能促进了水体富营养化和内源输入的增强. 在两个湖泊中, 营养水平的上升和内源生产力的增加促进了有机碳含量的快速增加. 进一步分析表明, 近百年来长湖有机碳与无机碳含量变化的同步性明显(r=0.54, P＜0.001)而在月湖中无显著关系(P=0.20, P>0.05). 两个湖泊中沉积通量的变化均与全岩C∶N比值呈显著正相关(r=0.48和0.45, P≤0.001), 且有机碳与无机碳埋藏通量均呈现同步变化的显著特征(r=0.72和0.85, P＜0.001). 其中长湖的无机碳埋藏通量显著高于有机碳埋藏通量, 而月湖的有机碳埋藏通量略高于无机碳埋藏通量, 反映了岩溶地区流域外源输入和水体富营养化的差异性驱动影响. 在流域开发增强的梯度下, 森林退化会降低流域碳输出的负荷, 而农业扩张和水体富营养化会促进藻类生长和内源有机碳的累积. 因此, 流域土地利用和水体营养水平对湖泊无机碳和有机碳埋藏变化的长期轨迹和协同模式产生了重要影响, 对喀斯特地区的碳库评估需要考虑无机碳循环的重要性.;Catchment-scale exports of organic and inorganic carbon plays an important role in affecting the lake sediment carbon burial. Inorganic carbon cycling in Karst landscapes is sensitive to human activities due to the rapid kinetics of carbonate dissolution. As with intensive watershed development, the source, content and burial loading of organic and inorganic carbon in Karst region may show a synchronous change. This study selected two medium-sized lakes (Lake Changhu and Lake Yuehu) with contrasting land uses patterns in the Shilin Karst area of central Yunnan for sediment surveys. With the proxies analyses for soil erosion (i.e. magnetic susceptibility (MS)), catchment allochthonous input (C∶N ratio), lake hydrology (particle size), nutrient levels (total phosphorus and nitrogen) and primary production (i.e. algal pigments), together with monitoring data and historical records, the history of limnological changes and catchment development over the last century for both lakes were reconstructed. Furthermore, long-term variation and synchronic pattern of sediment organic carbon (OC) and inorganic carbon (IC) burial in the context of catchment development were quantified. The sediment MS signal recorded the fluctuation in soil erosion intensity and a general pattern of long-term nutrient enrichment in both lakes. In Lake Changhu, with a higher land cover of forest (33.43%), the bulk and organic C∶N ratios were positively related with the MS signal (r=0.95 and 0.89, P < 0.001) but showed a negative relationship with sediment inorganic and organic carbon content (r=-0.94, P < 0.001 and -0.52, P=0.01), respectively, reflecting a significant impact of catchment carbon input. In Lake Yuehu, with a current land cover dominated by the cropland (60.98%), the bulk and organic C∶N ratios were negatively related with the MS signal (r=-0.54, P < 0.01 and -0.67, P < 0.001) and the bulk C∶N ratio showed no relationship with the sediment inorganic content (P=0.15), reflecting that the cropland expansion may have enhanced lake eutrophication and autochthonous input. In both lakes, nutrient enrichment and algal production enhanced the rapid OC accumulation. Additional analyses showed that there existed a significantly synchronous change between OC and IC content in Lake Changhu (r=0.54, P < 0.001) but not in Lake Yuehu (P=0.20, P>0.05). In both lakes, sediment loading was positively related with bulk C∶N ratio (r=0.48 and 0.45, P≤0.001), and there also existed a significantly synchronous change between OC and IC loadings (r=0.72 and 0.85, P < 0.001). Furthermore, the IC burial rate was significantly higher than that of OC in Lake Changhu, while IC consistently lower than OC in the nutrient-rich Lake Yuehu, reflecting differential forcing of vegetation degradation and lake eutrophication. With the intensive development in watershed, forest degradation can reduce the loading of catchment carbon export, while agricultural expansion and eutrophication would promote the growth of algae and the OC accumulation rate. Therefore, land use and lake nutrient levels can significantly impact the long-term trajectory and synchronic variation of sediment OC and IC burial. Thus, IC cycling should be considered in the regional assessment of carbon stock in karst areas.

Controls on the Presence and Concentration of Soil Inorganic Carbon in a Semi-Arid Watershed

Controls on the Presence and Concentration of Soil Inorganic Carbon in a Semi-Arid Watershed

Scanning electron microscope analysis of Emiliania huxleyi samples revealed the presence of a single morphotype in the Dardanelles Strait, Turkey

The cosmopolitan coccolithophorid, Emiliania huxleyi form populations composed of diferent morphotypes distinguished based on coccolith ultrastructure. The relative abundance of these morphotypes varies along the gradients of several environmental factors, including temperature, pH and nutrients, with significant ecological and biogeochemical outcomes as morhotypes difer in the calcite content, hence in their contributions to the downward carbonate transport. A scanning electron microscope examination of Emiliania huxleyi cells and coccoliths was conducted on samples from an Emiliania huxleyi dominated coastal phytoplankton community formation captured on the 29th and 31th of May 2019, performing a morphological and morphometric analysis and an assessment of the environmental nutrient characteristics. The main aim of the study was to describe the morphotype from a highly important ecosystem with E. huxleyi blooms, the Dardanelles Strait, Turkey and contribute to the present scientific understanding of their ecological preferences. The satellite-derived chlorophyll a and particulate inorganic carbon concentrations data were also included to expand the spatio-temporal coverage of the study. The nutrient data suggested nitrogen limitation of the phytoplankton community in general and an additional silicate limitation of the diatoms. The microscopic observations of samples, coccosphere/coccolith counts and the morphologic and morphometric examination of the coccoliths showed the presence of an E. huxleyi bloom solely composed of morphotype A. Furthermore, the satellite data showed the coccolithopore bloom started in the interconnected basin of the Black Sea and progressed into the Dardanelles via the Sea of Marmara.

Humus of the brown soils of the mountain pastures of Uzbekistan

The aim of the study: assessment of humus content and its distribution in the profile of brown soils of mountain pastures in Uzbekistan. Location and time of the study. Soil pits were cut in the Republic of Uzbekistan in seven agricultural regions, widely used in agriculture: Tashkent region, Bustonlik district; Jizzakh region, Zomin district; Samarkand region, Nurabad district; Navoi region, Nurata district; Kashkadarya region, Kitab district; Surkhandarya region, Sherabad district; Namangan region, Papal district. The study was carried out in 2019-2021. Methods. Field studies, sampling and sample preparation were carried out in accordance with the generally accepted methods: soil organic carbon content was measured by bichromate digestion, carbonate content was determined by acidimetric method and soil inorganic carbon content was calculated by subtracting from the total content of carbonates. Silty fractions were isolated by centrifugation. Humus differentiation into reserves and their estimation was carried out according to the method proposed by one of the authors. Main results. The studied brown soils of mountain pastures of Uzbekistan are characterized by loamy granulometric composition, with a clay fraction not exceeding 20%. The content of carbonates is low (2.5–9%), with the maximum amount in the carbonate horizon. Soils are slightly leached. The total humus content in the upper horizon varies from 1% to 6.6%. The dependence of soil humus content on the slope exposure was noted: the soils of the more humid northern and western slopes contain more humus than the southern and eastern ones. In addition, the humus content is significantly affected by erosion. To assess the nature of changes in the organic matter of the brown soils during their agricultural use, humus of the near, labile and potential reserves (as percentage of the total content) was isolated for the first time. It was revealed that humus of potential reserve prevails in soils (35.5-90%). Its vertical distribution is characterized by a sharp decrease in the sub-humus part, while the humus of the near and labile reserves is distributed evenly in the profile, without a pronounced dependence on external conditions and the degree of disturbance. The proportion of insoluble organic substances in the total humus content ranged from 0.39 to 86%, of sparingly soluble organic substances - from 3 to 100%. There is a relationship between the amount of sparingly soluble and insoluble organic matter in the upper horizon and the degree of soil erosion. Conclusion. The distribution of humus and its reserves in the brown soils of the mountain pastures of Uzbekistan is uneven and strongly affected by erosion. The loss of near and labile humus reserves leads to a decrease in the content of total humus. Further study of humus features, humus accumulation and restoration in brown soils is important for the development of recommendations for the rational use, anti-erosion protection and increasing the productivity of mountain pastures in Uzbekistan.

Chemical Composition and Source Apportionment of PM2.5 in a Border City in Southwest China

This paper studied the chemical characteristics and seasonal changes of PM2.5 in plateau cities on the southwest border of China. Urban air was sampled in Baoshan City during the rainy and dry seasons. Finally, 174 PM2.5 filters were collected (including 87 quartz and 87 Teflon samples for PM2.5). The mass concentrations, water-soluble inorganic ions, organic and inorganic carbon concentrations, and inorganic elements constituting PM2.5 were determined. Positive definite matrix factorization was used to identify potential sources of PM2.5, and the backward trajectory model was used to calculate the contribution of the long-distance transmission of air particles to the Baoshan area. It was found that in the wet season, most of the air masses come from the Indian Ocean and Myanmar. In the dry season, the air mass mainly comes from the China and Myanmar border area. The average concentration of PM2.5 in the wet and dry seasons was 23.17 ± 12.23 μg/m3. The daily mean value of OC/EC indicated that the measured SOC content was generated by the photochemical processes active during the sampling days. However, elements from anthropogenic sources (Na, Mg, Al, Si, P, K, Ca, Ti, Fe, Cu, Zn, Sb, Ba, and Pb) accounted for 99.51% and 99.40% of the total inorganic elements in the wet season and dry season, respectively. Finally, source apportionment showed that SIA, dust, industry, biomass burning, motor vehicle emissions, and copper smelting emissions constituted the major contributions of PM2.5 in Baoshan. Using combined data from three measurement sites provides a focus on the common sources affecting all locations.

Does Turbulent-Flow Conditioning of Irrigation Water Influence Soil Chemical Processes: I. Laboratory Results

ABSTRACT Researchers commonly assume that the intrinsic behavior of molecular water is invariable, yet accumulating evidence suggests that water behavior can be modified via non-chemical means, e.g. by magnetic field effects. This laboratory study examined the effect of turbulent-flow conditioning (CTap) of a mineralized irrigation water source (Tap water) on water chemistry and the behavior and character of soil–water interactions. Turbulent conditioning did not alter the chemistry of water itself; dissolved organic and inorganic carbon, nitrate, ammonium, chloride, dissolved oxygen, and nutrient element concentrations were the same both before and after treatment. However, turbulent conditioning slightly reduced the surface tension of CTap water relative to Tap. Results indicate that CTap irrigation water changed the chemical composition in one pore volume of water leached through the soil column; consistently increasing mean potassium, ammonium, magnesium, and calcium concentrations by 1.2- to 1.4-fold compared to untreated Tap water. Results for the micro-nutrients were inconclusive because their concentrations in the waters were below the analytical detection limit. Conditioning may have changed physical properties of the CTap water, which altered the nature of its physical and/or chemical interactions with the soil. A consistent effect develops after incubated soil is irrigated for >4-weeks, suggesting that the treatment impacts on soil properties may accumulate over time, potentially influencing soil productivity and management. This phenomenon deserves to be further investigated; if the capacity of this simple device to increase soil cation leaching can be confirmed, it could potentially provide an economical means of managing salt-affected soils.

Sensitivity analysis in a radiological impact assessment of a nuclear power plant discharge. A comparison of the Morris, Spearman and Sobol’ approaches

This paper compares the Morris, Spearman and Sobol’ methods of sensitivity analysis in radiological risk assessment. The determination of the most influential parameters on model with regards to the propagation of their uncertainties to output variables, is of greatest interest. This study aims to determine the relative importance of parameters uncertainties on the dose calculation uncertainty in the framework of a scenario of routine discharges discussed in the context of an IAEA working group. The scenario considers atmospheric and liquid discharges of three different types of radionuclides (14C, tritium as HTO and 110mAg) from a nuclear power plant located by the side of a river. It is concluded that the most reliable and practical method according to the ability of ranking influential parameters and the easiness of its application is the Spearman method. As key result, the three first influential variables for annual total dose for all pathways and all radionuclides were the water dissolved inorganic carbon concentration, the volatilisation rate constant and the soil layer solid liquid distribution in 14C.

Exploring Spatially Explicit Changes in Carbon Budgets of Global River Basins during the 20th Century.

Rivers play an important role in the global carbon (C) cycle. However, it remains unknown how long-term river C fluxes change because of climate, land-use, and other environmental changes. Here, we investigated the spatiotemporal variations in global freshwater C cycling in the 20th century using the mechanistic IMAGE-Dynamic Global Nutrient Model extended with the Dynamic In-Stream Chemistry Carbon module (DISC-CARBON) that couples river basin hydrology, environmental conditions, and C delivery with C flows from headwaters to mouths. The results show heterogeneous spatial distribution of dissolved inorganic carbon (DIC) concentrations in global inland waters with the lowest concentrations in the tropics and highest concentrations in the Arctic and semiarid and arid regions. Dissolved organic carbon (DOC) concentrations are less than 10 mg C/L in most global inland waters and are generally high in high-latitude basins. Increasing global C inputs, burial, and CO2 emissions reported in the literature are confirmed by DISC-CARBON. Global river C export to oceans has been stable around 0.9 Pg yr–1. The long-term changes and spatial patterns of concentrations and fluxes of different C forms in the global river network unfold the combined influence of the lithology, climate, and hydrology of river basins, terrestrial and biological C sources, in-stream C transformations, and human interferences such as damming.

High-Resolution Reanalysis of the Mediterranean Sea Biogeochemistry (1999–2019)

Ocean reanalyses integrate models and observations to provide a continuous and consistent reconstruction of the past physical and biogeochemical ocean states and variability. We present a reanalysis of the Mediterranean Sea biogeochemistry at a 1/24° resolution developed within the Copernicus Marine Environment Monitoring Service (CMEMS) framework. The reanalysis is based on the Biogeochemical Flux Model (BFM) coupled with a variational data assimilation scheme (3DVarBio) and forced by the Nucleus for European Modeling of the Ocean (NEMO)–OceanVar physical reanalysis and European Centre for medium-range weather forecasts (ECMWF) reanalysis ERA5 atmospheric fields. Covering the 1999–2019 period with daily means of 12 published and validated biogeochemical state variables, the reanalysis assimilates surface chlorophyll data and integrates EMODnet data as initial conditions, in addition to considering World Ocean Atlas data at the Atlantic boundary, CO2 atmospheric observations, and yearly estimates of riverine nutrient inputs. With the use of multiple observation sources (remote, in situ, and BGC-Argo), the quality of the biogeochemical reanalysis is qualitatively and quantitatively assessed at three validation levels including the evaluation of 12 state variables and fluxes and several process-oriented metrics. The results indicate an overall good reanalysis skill in simulating basin-wide values and variability in the biogeochemical variables. The uncertainty in reproducing observations at the mesoscale and weekly temporal scale is satisfactory for chlorophyll, nutrient, oxygen, and carbonate system variables in the epipelagic layers, whereas the uncertainty increases for a few variables (i.e., oxygen and ammonium) in the mesopelagic layers. The vertical dynamics of phytoplankton and nitrate are positively evaluated with specific metrics using BGC-Argo data. As a consequence of the continuous increases in temperature and salinity documented in the Mediterranean Sea over the last 20 years and atmospheric CO2 invasion, we observe basin-wide biogeochemical signals indicating surface deoxygenation, increases in alkalinity, and dissolved inorganic carbon concentrations, and decreases in pH at the surface. The new, high-resolution reanalysis, open and freely available from the Copernicus Marine Service, allows users from different communities to investigate the spatial and temporal variability in 12 biogeochemical variables and fluxes at different scales (from the mesoscale to the basin-wide scale and from daily to multiyear scales) and the interaction between physical and biogeochemical processes shaping Mediterranean marine ecosystem functioning.

Geochemical partition of chemical elements in Kastanozems and Solonetz in a local catchment within a semiarid landscape of SW Russia

The vertical and lateral migrations of chemical elements (ChEs) under semiarid conditions were studied in a soil catena within the uppermost local catchment (2 ha) in the NE part of the Ergeni Upland (the NW Kalmykia, SW Russia). The data were interpreted using the key soil properties typically influencing the mobilisation and accumulation capacity of ChEs: pH, electrical conductivity and soil organic and inorganic carbon content as well as clay, silt and sand fractions. The patterns of the vertical distributions of ChEs were similar in all soils (Kastanozems and Solonetz) irrespective of their topographic location, but the depth of translocation was larger in the gully bottom. The content of mobile fractions of Ca, Mn and, to a lesser extent, P was higher than a residual fraction, which means that these elements have the highest potential mobility in soils (considering the sum of the three mobile fractions: weakly bound acid-soluble, bound with complexes and (hydr)oxides of Fe and Mn). In Kastanozems and Solonetz, weakly bound acid-soluble forms of the readily soluble ChEs (B, Ca, K, Na and Sr), and acid-soluble compounds (of Cd, Fe, K, Na and P) as well as both acid-soluble compounds and complexes for biogenic heavy metals (Co, Cu and Mn) are the major actors of geochemical migration. In the gully catchment, spatial differentiation is governed by the availability of water and the presence of readily soluble compounds of B, Cl, Li, Na and S. Within the topsoil of Kastanozems and Solonetz, the mobility of ChEs decreases in the following order: Mn, Ca > Pb, Co, Cu > V, Ba, Zn > Fe, Al > K, Cr > Si and Ti. In Kastanozems and Solonetz, mobile B, Ca, K, Na, Sr and, to a lesser extent, Mg (in the whole soil profiles) as well as Ba, Be, Mo and S (in subsoil and parent materials) are weakly bound by carbonate and exchangeable compounds. Mobile Co, Cu and Mn are held by soil organic and inorganic complexes. Mobile Cd and Fe occurred mostly within compounds extracted by 1 M nitric acid. The content of elements differed from the parent materials more strongly in the topsoil of Kastanozems due to the accumulation of substances at the biogeochemical barrier in the A-horizon and in the subsoil of Solonetz due to the accumulation of substances at the sorption barrier in the natric horizon. The ‘Solonetz at microhighs–Kastanozems at microdepressions’ is a translocation-solutional microcatena due to the migration of the most mobile chemicals in the soil solution in spring (downward movement) and the dry season (upward movement). Furthermore, the 'Kastanozems at the interfluve–Kastanozems at the gully bottom' is a leaching catena due to the downward movement of less mobile chemicals with melted snow and meteoric water.

Geographical settings and tree diversity influenced soil carbon storage in different forest types in Rajasthan, India

Knowledge of soil-forest relationship in degraded dry forest ecosystem of Rajasthan is essential to understand the factors responsible for soil carbon storage in different forest types and devising climate change mitigation strategies. About 15% forest blocks across forest ranges in Rajasthan were surveyed by laying 903 plots of 0.1 ha area. Trees and shrubs were enumerated and measured and litter and coarse woody debris (CWD) were quantified. Soil samples were collected from 0 to 30, 30–60 and 60–90 cm soil layers and analysed for pH, electrical conductivity (EC), bulk density (BD), gravel (G), organic (SOC) and inorganic (SIC) carbon contents. Species richness (SR), Shannon-Weiner diversity (H′) and SOC and SIC stocks were calculated. Thirty-one forest types identified that differed (p < 0.05) in trees/shrubs SR and H′, litter and CWD, and soil parameters except SIC content/stock. SR and H′ were highest in Dry Bamboo Brakes and Riverain Forest for trees and in Secondary Dry Deciduous Forest and Dry Grassland for shrubs respectively. Soil carbon stock was highest in 0–30 cm soil layer, but SOC content/stock decreased and other soil variables increased with increase in soil depth. SIC stock showed greater (41.3-fold) spatial variation than SOC stock (4.2-fold) and were associated with forest types, elevation, rainfall and soil characteristics. Tree SR and H′ favoured SOC stock, but not the SIC stock signifying the role of pedogenic process and parent materials on SIC sequestration. Conclusively, plant species richness and diversity facilitated sequestration and storage of soil carbons in forests and plantations, but carbon stock of 33.43 Mg ha−1 SOC and 49.31 Mg ha−1 SIC in top 100 cm soil layer in Rajasthan forests indicated the influence of many factors on total carbon pool in this dry area.

Long‐term vegetation restoration increases carbon sequestration of different soil particles in a semi‐arid desert

AbstractVegetation restoration in desert areas has an important influence on soil carbon sequestration. To understand the long‐term effects of vegetation restoration on soil particle composition and carbon sequestration of different soil particles in semi‐arid deserts, we collected the topsoil of different types of vegetation restored for different periods at the southeast margin of Mu Us Desert and analyzed the soil organic carbon (SOC) and soil inorganic carbon (SIC) contents in soil particles of different sizes. The results demonstrated that after vegetation restoration, soil particles of &lt;0.05 mm and aggregates in arbor lands and shrub lands increased 8 and 4 times and 4.67 and 4 times than shifting sandy land (CK), respectively. The SOC and SIC in different soil particles under vegetation increased with the restoration period. Among different vegetation forms, arbor land had significant effect on SIC fixation. Soil particles of &lt;0.05 mm contained the highest SOC and SIC contents (16.8 and 0.78 g/kg), followed by aggregates (8.26 and 6.79 g/kg), 0.05–0.25 mm (8.24 and 4.55 g/kg), and &gt;0.25 mm (5.23 and 2.25 g/kg). As for total SOC storage, it was positively correlated with the organic carbon storage of &lt;0.05 mm particles. We concluded that SOC and SIC of &lt;0.05 mm soil particles and aggregates increase with the restoration period and play a leading role in soil carbon sequestration. From the perspective of long‐term soil carbon sequestration, the best vegetation restoration mode in Mu Us Desert would be arbor forest.

Effect of inorganic carbon limitation on the nitrogen removal performance of the single-stage reactor containing anammox and nitritation gel carriers

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 Km value of nitritation was calculated as 4.4mg-C L-1. In anammox reactor, it was calculated as 1.7mg-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.

Increasing sulfate concentration and sedimentary decaying cyanobacteria co-affect organic carbon mineralization in eutrophic lake sediments

Sulfate (SO42−) concentrations in eutrophic lakes are continuously increasing; however, the effect of increasing SO42− concentrations on organic carbon mineralization, especially the greenhouse gas emissions of sediments, remains unclear. Here, we constructed a series of microcosms with initial SO42− concentrations of 0, 30, 60, 90, 120, 150, and 180 mg/L to study the effects of increased SO42− concentrations, coupled with cyanobacterial blooms, on organic carbon mineralization in Lake Taihu. Cyanobacterial blooms promoted sulfate reduction and released a large amount of inorganic carbon. The SO42− concentrations in cyanobacteria treatments significantly decreased and eventually reached close to 0. As the initial SO42− concentration increased, the sulfate reduction rates significantly increased, with maximum values of 9.39, 9.44, 28.02, 30.89, 39.68, and 54.28 mg/L∙d for 30, 60, 90, 120, 150, and 180 mg/L SO42−, respectively. The total organic carbon content in sediments (51.16–52.70 g/kg) decreased with the initial SO42− concentration (R2 = 0.97), and the total inorganic carbon content in overlying water (159.97–182.73 mg/L) showed the opposite pattern (R2 = 0.91). The initial SO42− concentration was positively correlated with carbon dioxide (CO2) emissions (R2 = 0.68) and negatively correlated with methane (CH4) emissions (R2 = 0.96). The highest CO2 concentration and lowest CH4 concentration in the 180 mg/L SO42− treatment were 1688.78 and 1903 μmol/L, respectively. These biogeochemical processes were related to competition for organic carbon sources between sulfate reduction bacteria (SRB) and methane production archaea (MPA) in sediments. The abundance of SRB was positively correlated with the initial SO42− concentration and ranged from 6.65 × 107 to 2.98 × 108 copies/g; the abundance of MPA showed the opposite pattern and ranged from 1.99 × 108 to 3.35 × 108copies/g. These findings enhance our understanding of the effect of increasing SO42− concentrations on organic carbon mineralization and could enhance the accuracy of assessments of greenhouse gas emissions in eutrophic lakes.

Disentangling the Effects of Ocean Carbonation and Acidification on Elemental Contents and Macromolecules of the Coccolithophore Emiliania huxleyi.

Elemental contents change with shifts in macromolecular composition of marine phytoplankton. Recent studies focus on the responses of elemental contents of coccolithophores, a major calcifying phytoplankton group, to changing carbonate chemistry, caused by the dissolution of anthropogenically derived CO2 into the surface ocean. However, the effects of changing carbonate chemistry on biomacromolecules, such as protein and carbohydrate of coccolithophores, are less documented. Here, we disentangled the effects of elevated dissolved inorganic carbon (DIC) concentration (900 to 4,930μmolkg−1) and reduced pH value (8.04 to 7.70) on physiological rates, elemental contents, and macromolecules of the coccolithophore Emiliania huxleyi. Compared to present DIC concentration and pH value, combinations of high DIC concentration and low pH value (ocean acidification) significantly increased pigments content, particulate organic carbon (POC), and carbohydrate content and had less impact on growth rate, maximal relative electron transport rate (rETRmax), particulate organic nitrogen (PON), and protein content. In high pH treatments, elevated DIC concentration significantly increased growth rate, pigments content, rETRmax, POC, particulate inorganic carbon (PIC), protein, and carbohydrate contents. In low pH treatments, the extents of the increase in growth rate, pigments and carbohydrate content were reduced. Compared to high pH value, under low DIC concentration, low pH value significantly increased POC and PON contents and showed less impact on protein and carbohydrate contents; however, under high DIC concentration, low pH value significantly reduced POC, PON, protein, and carbohydrate contents. These results showed that reduced pH counteracted the positive effects of elevated DIC concentration on growth rate, rETRmax, POC, PON, carbohydrate, and protein contents. Elevated DIC concentration and reduced pH acted synergistically to increase the contribution of carbohydrate–carbon to POC, and antagonistically to affect the contribution of protein–nitrogen to PON, which further shifted the carbon/nitrogen ratio of E. huxleyi.

Could Land Abandonment with Human Intervention Benefit Cropland Restoration? From the Perspective of Soil Microbiota

Although agricultural land abandonment (LA) is accompanied by land degradation, it could be considered a kind of self-rehabilitation. Studies have shown that long-term LA has profound ecological and environmental benefits, whereas few studies have compared LA with human intervention (HI), which involves planting and fertilization in agroecosystem restoration. Here, we established four different scenarios based on local livestock husbandry, including LA without HI, LA with slight human intervention (HIS), medium human intervention (HIM), and intensive human intervention (HII). LA experiments were conducted for 3 years and repeatedly sampled three times. The soil bacterial and fungal communities were determined to present the ecological impacts. In this study, LA and HIS could save soil inorganic carbon and total calcium (Ca) contents and benefit soil mycorrhizal fungi and plant growth-promoting rhizobacteria. LA and HIM benefited some microbial communities associated with complicated organic compounds. Human interference methods did not significantly increase soil nutrients after 3 years of farmland abandonment. However, indigenous vegetation increased the risk of plant diseases based on soil microbial communities. Forage grass may control the risk, and HIS was a cost-effective scenario in our study. Moreover, we should maintain a cautious attitude toward HII to prevent excessive intervention.