Inorganic Carbon Concentrations Research Articles

Changes in deep Pacific circulation and carbon storage during the Pliocene-Pleistocene transition

The global climate has been gradually cooling over the Cenozoic and is punctuated by the intensification of Northern Hemisphere Glaciation (NHG) from the latest Pliocene to earliest Pleistocene (∼3.1–2.5 millions of years ago, Ma). A decline of atmospheric CO2 is supposed as a prerequisite for the NHG, but the associated carbon-cycle processes remain elusive. Here we combine foraminiferal records of neodymium isotope and boron-calcium ratio, and simulations of an Earth system model, to investigate changes in the water-mass composition and carbonate-ion concentration of the deep Pacific Ocean during the NHG. Our proxy records have revealed a significant expansion of southern-sourced waters with increased respired carbon storage into the deep Pacific during the NHG. These changes may be explained by strengthened deep-water formation and biological-pump efficiency in the Southern Ocean due to Antarctic sea-ice growth, as suggested by our model experiments and evidence from the Sub-Antarctic region. These results provide key clues for quantifying the role of the dissolved inorganic carbon content of deep Pacific waters in modulating atmospheric CO2 during the NHG.

Meridional Variability in Multi‐Decadal Trends of Dissolved Inorganic Carbon in Surface Seawater of the Western North Pacific Along the 165°E Line

AbstractMulti‐decadal trends of the total dissolved inorganic carbon (DIC) concentrations and consequent ocean acidification in surface seawater were investigated on the basis of data from shipboard measurements conducted since 1996 along the 165°E repeat line in the western North Pacific. The observed trends exhibited clear meridional variabilities, with higher rates in the subtropical and tropical zones and lower rates in the subarctic zone, with a DIC range from +0.09 ± 0.14 to +1.64 ± 0.16 μmol kg−1 yr−1 and pH range from −0.0023 ± 0.0034 to −0.0281 ± 0.0059 decade−1. DIC and acidification trends were consistent with those expected from the atmospheric CO2 concentrations at nearly all latitudinal zones, but were significantly different at some latitudes. We attribute the significantly lower rates observed in the central western Subarctic Gyre and southern Subtropical Gyres primarily to the variabilities in upward DIC supply from the subsurface associated with the variability in ocean circulation. However, the higher rate observed to the south of the Kuroshio Extension appears to have been caused by the change in winter vertical mixing related to the change in its stable/unstable paths.

Making Salt from Water: The Unique Mineralogy of Alkaline Lakes

Alkaline lakes have some of the most unique and diverse known mineral assemblages as a result of their very high pH and dissolved inorganic carbon concentrations. In these closed-basin systems, aqueous geochemistry and mineralogy are intimately linked, whereby the removal of elements through mineral precipitation controls the lake water geochemistry. The resulting extreme water chemistry of alkaline lakes produces minerals that are rare in other environments, including low-temperature minerals that record valuable environmental information and that are commonly extracted as mineral resources. Alkaline lakes are also excellent environments to study various processes in mineral crystallization, growth, and transformation, including the formation of metastable phases, precipitation after extreme supersaturation, co-precipitation of minerals, and the influence of dynamic conditions.

The marine carbonate system variability in high meltwater season (Spitsbergen Fjords, Svalbard)

The spatial variability in hydrography (salinity and temperature) and carbonate chemistry (alkalinity - AT, total inorganic carbon concentration - CT, pH, CO2 partial pressure - pCO2, and the saturation state of aragonite - ΩAr) in high meltwater season (summer) was investigated in four Spitsbergen fjords - Krossfjorden, Kongsfjorden, Isfjorden, and Hornsund. It was found that the differences in hydrology entail spatial changes in the CO2 system structure. AT decline with decreasing salinity was evident, hence it is clear that freshwater input generally has a diluting effect and lowers AT in the surface waters of the Spitsbergen fjords. Significant surface water AT variability (1889–2261 µmol kg−1) reveals the complexity of the fjords’ systems with multiple freshwater sources having different alkalinity end-member characteristics and identifies the mean AT freshwater end-member of 595 ± 84 µmol kg−1 for the entire region. The effect of AT fluxes from sediments on the bottom water was rather insignificant, despite high AT values (2288–2666 μmol kg−1) observed in the pore waters. Low pCO2 results in surface water (200–295 μatm) points to intensive biological production, which can strongly affect the CT values, however, is less important for shaping alkalinity. It has also been shown that the freshening of the surface water in the fjords reduces significantly ΩAr (an increase in freshwater fraction contribution by 1% causes a decrease in ΩAr by 0.022). Although during the polar day, due to low pCO2, ΩAr values are still rather far from 1 (they ranged from 1.4 to 2.5), during polar night, when pCO2 values are much higher, ΩAr may drop markedly. This study highlights that the use of salinity to estimate the potential alkalinity can carry a high uncertainty, while good recognition of the surface water AT variability and its freshwater end-members is key to predict marine CO2 system changes along with the ongoing freshening of fjords waters due to climate warming.

Distinct lake sedimentary imprints of earthquakes, floods and human activities in the Xiaojiang Fault zone: Towards a quantitative paleoseismograph in the southeastern Tibetan Plateau

Lake sediments that widely distributed in the active and complicated fault zones have been recently showing great potential for paleoseismic reconstruction. However, flood events and human activities may make the seismic signal unrecognizable. In this study, high-resolution analyses of sedimentary structure, physical and chemical proxies, as well as absolutely radioactive dating were conducted on seven representative sediment cores from the depocenter, nearshore and inlet areas of Yangzong Lake, a typical fault lake in the Xiaojiang Fault zone, southeastern Tibetan Plateau (TP). These new data were calibrated by historical documents, suggesting that seismically induced mass-transport deposits (MTDs, i.e., turbidites) were massive and/or amalgamated (earthquake doublet), became fining and thickening towards the lake center (without changing lake morphology), and occasionally exhibited soft sediment deformation structures (SSDs, i.e., microfaults). These sediments were relatively poorly sorted and instantaneously deposited from slope failures within the lake. An extremely strong earthquake could cause coseismic subsidence of the lake basin and destruct the local hydrological system, resulting in exceptionally high Mn and total inorganic carbon (TIC) contents in the lake center. In contrast, flood deposits were thinner with horizontal beddings, had higher terrestrial organic matter (higher C/N ratios), and distributed locally in the lake inlet area. Human activities-induced sediments were inversely graded, poorly sorted and gradually deposited, had horizontal beddings and no erosive base, and exhibited high carbon, Pb and Zn contents and low C/N ratios. In addition, macroseismic investigations and statistical results from intensity prediction equations (IPEs) provided a conservative threshold of ∼8 Modified Mercalli Intensities (MMI) for triggering turbidites, and a ∼ 10 MMI for inducing coseismic subsidence and hydrological destruction. This study was among the first attempts to establish a quantitative lacustrine paleoseismograph in the southeastern TP, and the new results would greatly improve the valid assessment of geohazard risks.

Basic techniques of mound construction of the Yamnaya culture in the Southern Urals

The aim of the study. To determine the material and basic techniques for constructing burial mounds (kurgans) of the Yamnaya culture of the Bronze Age in the Southern Urals based on a comprehensive analysis with an emphasis on meso- and micromorphological analysis. Location and time of the study. The research objects are located in the Orenburg region within the East European Plain. Security excavations were carried out in 2019-2022 at three burial mounds located in the Tashlinsky (mound burial grounds Boldyrevo IV and Tashla IV) and Grachevsky districts (kurgan burial ground Kalikino II) of the Orenburg region. Mound 1 in the Boldyrevo IV burial mound, due to its significant size of 4.2 m in height and 60 m in diameter was chosen as a key object for which a full survey was carried out. Additionally, the smaller in size mounds of the 1st burial mound Tashla IV, as well as 1, 4 and 5 of the Kalikino II burial mound were studied. Methods. To determine the source of building materials and the basic techniques of soil and ground subsoil substrates for mound construction, a comprehensive analysis was carried out with an emphasis on macro-, meso- and micromorphological properties of the substrates. For the analytical study, which was carried out only for the Boldyrevo IV mound 1, total carbon content, organic and inorganic (carbonates) carbon content, loss on ignition, particle size distribution, magnetic susceptibility and pH were determinied. Results. The structure and materials of five burial mounds of the Yamnaya culture of the Bronze Age (5500 - 4300 years ago) were studied. The kurgans were proven to have been built from the local soils with the addition of anthropogenic material (silt, bones, shells). Representatives of the Yamnaya culture created variegated flowers using the construction techniques such as kneading, ramming, and the inclusion of anthropogenic material. At the micromorphological level, these techniques produces patterns of light loose and more compacted dark microzones in construction materials. Conclusions. Based on meso- and micromorphological analysis of the studied mound structures, we conclude that the representatives of the Yamnaya culture had knowledge of construction technologies and used them appropriately. The main method of mound constructing was creating a variegated mixed soil from humus or carbonate horizons with admixtures of anthropogenic and carbonate material. When building small mounds, people used rough kneading and tamping, but for larger mounds, either more complex construction was used, or more thorough kneading and tamping, as well as longer exposure to water.

Prediction of CO<sub>2</sub>, CH<sub>4</sub> diffusion fluxes at the water-air interface and analysis on its influencing factors using machine learning algorithms in the Three Gorges Reservoir

传统的水-气界面温室气体通量的监测方法具有诸多局限,对其影响因素的分析也大多基于数学统计层面。对此,本研究提供了一种较为新颖的研究和分析方法——基于机器学习的数据预测和分析。本研究采用2种经典机器学习算法——随机森林(RF)和支持向量机(SVM)和2种深度学习算法——卷积神经网络(CNN)和长短时记忆神经网络(LSTM),通过环境因素预测水库水-气界面CO₂和CH₄扩散通量。此外,采用RF中的特征重要性评估和经典算法决策树(DT),对环境因素和水库温室气体扩散通量的关系进行了全新角度的数据挖掘和分析。结果表明:深度学习算法的预测效果均较好,经典机器学习算法中RF预测效果显著优于SVM。LSTM和RF分别产生了最优的CO₂扩散通量和CH₄扩散通量的预测精度,均方根误差(RMSE)分别为0.424 mmol/(m²·h)和0.140 μmol/(m²·h),预测值与实测值的R²分别为0.960和0.758。RF的特征重要性评估表明沉积物因子和营养因子均为影响CO₂和CH₄扩散通量的关键因子,气候因子和水环境因子相较次之。采用决策树描绘决定CO₂扩散通量源和汇的环境因子的极限阈值,决策树对所有样本的分类准确性高达100%,且其结果还表明低浓度的溶解无机碳和碱性条件有利于水体成为CO₂汇。因此,使用机器学习算法预测和分析水库水-气界面温室气体通量的潜力巨大。;Traditional methods for monitoring greenhouse gas fluxes at the water-air interface in reservoirs have many limitations. The analysis on its influencing factors is also mainly based on mathematical statistics. This study provides an innovative approach by using machine learning algorithms. In this study, two traditional machine learning algorithms (Random forests (RF) and Support vector machine (SVM)) and two deep learning algorithms (Convolutional neural network (CNN) and long and short term memory neural network (LSTM)) were applied to predict CO₂ and CH₄ diffusion fluxes. In addition, the feature importance assessment in RF and the decision tree (DT) are used to analyze the relationship between environmental factors and GHG diffusion fluxes in reservoirs from a new perspective. The results showed that deep learning produced excellent prediction accuracy, whereas prediction accuracy of RF was significantly better than SVM in traditional machine learning. LSTM and RF yielded optimal accuracy in predicting CO₂ flux and CH₄ flux, respectively. The root mean square error (RMSE) was 0.424 mmol/(m²·h) and 0.140 μmol/(m²·h) and R² of the predicted and measured values were 0.960 and 0.758, respectively. RF identified sediment and nutrient as critical environmental factors to GHG fluxes, followed by climate factors and water environment factors. Lastly, a decision tree was used innovatively to depict the limiting threshold of environmental factors that determines the source or sink of CO₂. The classification accuracy of this decision tree is as high as 100% in this study. The results of decision tree also showed that low dissolved inorganic carbon concentration and alkaline conditions are favorable for water to absorb atmospheric CO₂. These results demonstrate the great potential of using machine learning algorithms to predict and analyze GHG fluxes at the water-air interface in reservoirs.

The role of groundwater in CO2 production and carbon storage in Mediterranean peatlands: An isotope geochemistry approach

Peatlands are permanent wetlands recognized for ecosystem services such as biodiversity conservation and carbon storage capacity. Little information is available about their response to global change, the reason why most Earth system climate models consider a linear increase in the release of greenhouse gases (GHG), such as CO2, with increasing temperatures. Nevertheless, numerous studies suggest that an increase in the temperature may not imply a decrease in photosynthesis and carbon storage rates if water availability is sufficient, the latter being under the control of local hydrology mechanisms. Mediterranean peatlands well illustrate this fact. Since they are groundwater-dependent, they are hydrologically resilient to the strong seasonality of hydroclimatic conditions, especially during the summer drought. In the present study, we demonstrate that, even if such peatlands release CO2 into the atmosphere, they can maintain a carbon storage capacity. To this end, a geochemical study disentangles the origin and fate of carbon within a Mediterranean peatland at the watershed scale. Field parameters, major ions, dissolved organic and inorganic carbon content and associated δ13C values allow for characterizing the seasonality of hydrochemical mechanisms and carbon input from an alluvial aquifer (where rain, river, shallow, and deep groundwater flows are mixing) to the peatland. The inorganic and organic content of peat soil and δ13C values of total organic matter and CO2 complete the dataset, making it possible to provide arguments in favour of lower organic matter oxidation compared to primary production. Overall, this study highlights the groundwater role in the fluxes of CO2 at the peatland-atmosphere interface, and more broadly the need to understand the interactions between the water and carbon cycles to build better models of the future evolution of the global climate.

Soluble carbon loss through multiple runoff components in the shallow subsurface of a karst hillslope: Impact of critical zone structure and land use

In karst hillslopes, the soil-epikarst system is not only the main reservoir of soluble carbon, but also the hot spots of hydrological and biogeochemical processes. However, the soluble carbon loss mechanism through various runoff components occurring in the soil-epikarst system is not clear. We hypothesize that the karst critical zone structure determines the runoff and soluble carbon loss, and that these response processes can be regulated by land use. 12 experimental plots on a typical karst hillslope (each with 5 × 20 m projected area) of four land uses (naturally recovered shrubland, forage grassland, economic forest land, and cropland) were intensively instrumented for separately monitoring surface, subsurface, and epikarst seepage runoffs and their dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC) concentration. Results show that economic forest land had the highest total runoff and soluble carbon loss, followed by cropland, naturally recovered shrubland, and forage grassland. Generally, karst critical zone structure was the most important factors for controlling DOC and DIC loss through surface, subsurface, and epikarst seepage runoffs. Critical zones with thicker soil and less undulating soil-epikarst contact were more susceptible to runoff and soluble carbon loss. Although not as important as critical zone structures, land use can effectively regulate runoff and prevent soluble carbon loss by affecting rainfall partitioning in karst hillslopes. Planting forage grassland is an effective method of reducing carbon loss, due to its remarkable ability of reducing runoff in the soil-epikarst systems. Our results provide useful insights for determining appropriate land uses and optimizing soil and water conservation strategies in karst hillslopes.

Simulation of Smoldering Combustion of Organic Horizons at Pine and Spruce Boreal Forests with Lab-Heating Experiments

Wildfire is a threat for many boreal ecosystems and induces deep modifications in organic horizons. In this paper, we have considered fire-induced changes to the organic horizon properties. The effect of fire was studied by using a forest litter burning experiment. Sample heating was performed in the lab at fixed temperatures (200, 300 and 500 °C), on a set of O horizons developed under pine (Flavocetraria-Pinetum association) and spruce (Piceetum hylocomium splendens association) forest litters. Litters were analyzed in terms of pH, specific electrical conductivity, specific surface area, total carbon (Ctot) and nitrogen (Ntot) content, water-soluble carbon and nitrogen, δ13C and δ15N stable isotope analysis and 13C NMR spectroscopy. The mean pH values increased from ~5 to ~8.2 with an increase in the influence of temperature. The specific electrical conductivity and specific surface area properties increased as well from ~255 to ~432 and from 0.42 to 1.84, respectively. Ctot and Ntot decreased, but at the same time the inorganic carbon content increased. The aromaticity of organic matter after the fire increased. The results of the present study show that organic horizons are changed by wildfire and this discussion made it clear to help with the understanding how fire affects organic matter.

Measurement of DIC acquisition and evidence for a CO2 concentrating mechanism in Gephyrocapsa oceanica (Isochrysidales, Coccolithophyceae)

ABSTRACT The possession of a carbon concentrating mechanism (CCM) by a given phytoplankton species will in part determine its response to changes in the dissolved inorganic carbon concentrations in the global ocean. Earlier work on CCMs in the coccolithophore Emiliania huxleyi suggested that this species did not possess a CCM, though more recent studies indicate that a CCM is indeed present. Here we report work showing that another coccolithophore species, Gephyrocapsa oceanica, also possesses a functioning CCM, implying that increasing CO2 concentrations are unlikely to lead to enhanced growth rates. We discuss the protocol required for working with this species, noting that due to its liths being 10 or more times as massive as of those of Emiliania huxleyi, much lower centrifugation speeds (<400 × g) must be used to avoid damage to the cells.

Long‐term changes in dissolved inorganic carbon across boreal streams caused by altered hydrology

AbstractA major challenge for predicting future landscape carbon (C) balances is to understand how environmental changes affect the transfer of C from soils to surface waters. Here, we evaluated 14 yr (2006–2019) of stream dissolved inorganic carbon (DIC) concentration and export data for 14 nested boreal catchments that are subject to climatic changes, and compared long‐term patterns in DIC with patterns in dissolved organic carbon (DOC). Few streams displayed significant concentration or export trends in DIC at annual time scales. However, most streams showed decreasing DIC concentrations during spring flood over this 14‐yr period, and about half showed declines during summer. Although annual runoff has generally not changed during this period, an intra‐annual redistribution in runoff, with increases in spring flood discharge, explained much of the seasonal changes in DIC concentration. We observed negative DIC–discharge relationships in most streams, suggesting source limitation of DIC, whereas DOC mostly showed chemostatic behavior. The different trends and patterns observed for DIC vs. DOC underpin intra‐annual changes in the composition of the total C pool (i.e., the DIC/DOC ratio) and reflect fundamental differences in how these C forms are produced, stored in riparian soils, and mobilized by hydrological events. Collectively, our results highlight the sensitivity of riverine DIC to the intra‐annual distribution of runoff, but also important heterogeneity across the network that suggests local processes can also modify the mobilization of DIC in boreal landscapes.

IDENTIFICATION IN PORE WATERS OF RECYCLED SEDIMENT ORGANIC MATTER USING THE DUAL ISOTOPIC COMPOSITION OF CARBON (δ13C AND Δ14C): NEW DATA FROM THE CONTINENTAL SHELF INFLUENCED BY THE RHÔNE RIVER

ABSTRACTEstuaries and deltas are crucial zones to better understand the interactions between continents and oceans, and to characterize the mineralization and burial of different sources of organic matter (OM) and their effect on the carbon cycle. In the present study, we focus on the continental shelf of the northwest Mediterranean Sea near the Rhône river delta. Sediment cores were collected and pore waters were sampled at different depths at one station (Station E) located on this shelf. For each layer, measurements of dissolved inorganic carbon concentration (DIC) and its isotopic composition (δ13C and Δ14C) were conducted and a mixing model was applied to target the original signature of the mineralized OM. The calculated δ13C signature of the mineralized organic matter is in accordance with previous results with a δ13COM of marine origin that is not significantly impacted by the terrestrial particulate inputs from the river. The evolution with depth of Δ14C shows two different trends indicating two different Δ14C signatures for the mineralised OM. In the first 15 cm, the mineralized OM is modern with a Δ14COM = 100 ± 17‰ and corresponds to the OM produced during the nuclear period of the last 50 years. Deeper in the sediment, the result is very different with a depleted value Δ14COM = –172 ± 60‰ which corresponds to the pre-nuclear period. In these two cases, the marine substrate was under the influence of the local marine reservoir effect with more extreme Δ14C results. These differences can be largely explained by the influence of the river plume on the local marine DIC during these two periods.

Mineralization of autochthonous particulate organic carbon is a fast channel of organic matter turnover in Germany's largest drinking water reservoir

Abstract. Turnover of organic matter (OM) is an essential ecological function in inland water bodies and relevant for water quality. This is especially important for the potential of dissolved organic carbon (DOC) removal as well as for emissions of CO2. In this study, we investigated various phases of OM including DOC, autochthonous particulate organic carbon (auto-POC), allochthonous particulate organic carbon (allo-POC), and sedimentary matter (SED) in a temperate drinking water reservoir (Rappbode Reservoir, Germany) by means of dissolved inorganic carbon (DIC) concentrations and carbon stable isotope ratios. In order to best outline carbon turnover, we focused on the metalimnion and the hypolimnion of the reservoir, where respiration is expected to be dominant and hardly disturbed by atmospheric exchange or photosynthesis. DIC concentrations ranged between 0.30 and 0.53 mmol L−1, while δ13CDIC values ranged between −15.1 ‰ and −7.2 ‰ versus the VPDB (Vienna PeeDee Belemnite) standard. Values of δ13CDOC and δ13Cauto-POC ranged between −28.8 ‰ and −27.6 ‰ and between −35.2 ‰ and −26.8 ‰, respectively. Isotope compositions of sedimentary material and allochthonous POC were inferred from the literature and from measurements from previous studies with δ13CSED=-31.1 ‰ and δ13Callo-POC ranging from −31.8 ‰ to −28.6 ‰. Comparison of DIC concentration gains and stable isotope mass balances showed that auto-POC from primary producers was the main contributor to increases in the DIC pool. Calculated OM turnover rates (0.01 to 1.3 µmol L−1 d−1) were within the range for oligotrophic water bodies. Some higher values in the metalimnion are likely due to increased availability of settling auto-POC from the photic zone. Samples from a metalimnetic oxygen minimum (MOM) also showed dominance of respiration over photosynthesis. Our work shows that respiration in temperate lentic water bodies largely depends on auto-POC production as a major carbon source. Such dependencies can influence the vulnerabilities of these aqueous systems.

Non-Redfieldian carbon model for the Baltic Sea (ERGOM version 1.2) – implementation and budget estimates

Abstract. Marine biogeochemical models based on Redfield stoichiometry suffer from underestimating carbon fixation by primary production. The most pronounced indication of this is the overestimation of the dissolved inorganic carbon (DIC) concentration and, consequently, the partial pressure of carbon dioxide in surface waters. The reduced production of organic carbon will impact most biogeochemical processes. We propose a marine biogeochemical model allowing for a non-Redfieldian carbon fixation. The updated model is able to reproduce observed partial pressure of carbon dioxide and other variables of the ecosystem, like nutrients and oxygen, reasonably well. The additional carbon uptake is realized in the model by an extracellular release (ER) of dissolved organic matter (DOM) from phytoplankton. Dissolved organic matter is subject to flocculation and the sinking particles remove carbon from surface waters. This approach is mechanistically different from existing non-Redfieldian models which allow for flexible elemental ratios for the living cells of the phytoplankton itself. The performance of the model is demonstrated as an example for the Baltic Sea. We have chosen this approach because of a reduced computational effort which is beneficial for large-scale and long-term model simulations. Budget estimates for carbon illustrate that the Baltic Sea acts as a carbon sink. For alkalinity, the Baltic Sea is a source due to internal alkalinity generation by denitrification. Owing to the underestimated model alkalinity, an unknown alkalinity source or underestimated land-based fluxes still exist.

Isoetid mediated radial oxygen loss prevents iron reduction and the related mobilisation of ammonium and methane: an experimental approach

Isoetids are slow growing ecosystem-engineers that maintain an oligotrophic environment through high radial oxygen losses (ROL) from their roots. This ROL could potentially reduce methane (CH4) emission by maintaining sediment redox conditions unfavourable for methanogenesis. Isoetids have declined in many European countries as an effect of eutrophication and inorganic carbon enrichment. To assess the effect of sudden disappearance of isoetids on biogeochemical carbon and nutrient cycling in organic rich sediments, we set up a greenhouse experiment. Intact vegetated sediment patches with Lobelia dortmanna and Littorella uniflora were collected from ten boreal Norwegian softwater lakes. From half of the patches, isoetids were manually removed. We determined the effect of removal on sediment redox potential, pore water chemistry and CH4 emission. In addition, germination success of L. dortmanna seeds was tested on the sediments where isoetids were removed. The absence of ROL after isoetid removal led to a drop in sediment redox potential, resulting in anaerobic breakdown of organic matter using alternative electron acceptors, especially iron(hydr)oxides. Consequently, increased porewater concentrations of ammonium, iron, inorganic carbon and CH4 were observed in sediments where isoetids had been removed compared to the isoetid vegetated sediments. Moreover, over 20 times higher emission of CH4 was observed from the sediments where isoetids had been removed. On the highly reduced sediments, the germination of L. dortmanna was hampered. When isoetids are unable to recolonise after disturbance events, it is expected that the absence of ROL eventually results in a long-term increase in lake productivity and CH4 emission.

Multi-Horizon Predictive Soil Mapping of Historical Soil Properties Using Remote Sensing Imagery

There is increasing demand for more detailed soil maps to support fine-scale land use planning, soil carbon management, and precision agriculture in Saskatchewan. Predictive soil mapping that incorporates a combination of environmental covariates provides a cost-effective tool for generating finer resolution soil maps. This study focused on mapping soil properties for multiple soil horizons in Saskatchewan using historical legacy soil data in combination with remote sensing band indices, bare soil composite imagery, climate data, and terrain attributes. Mapped soil properties included soil organic carbon content (SOC), total nitrogen, cation exchange capacity (CEC), electrical conductivity (EC), inorganic carbon (IOC), sand and clay content, and total profile soil organic carbon stocks. For each of these soil properties, a recursive feature elimination was undertaken to reduce the number of features in the overall model. This process involved iteratively removing features such that random forest out-of-bag error was minimized. Final random forest models were built for each property and evaluated using an independent test dataset. Overall, predictive models were successful for SOC (R2 = 0.71), total nitrogen (R2 = 0.65), CEC (R2 = 0.46), sand content (R2 = 0.44) and clay content (R2 = 0.55). The methods used in this study enable mapping of a greater geographic region of Saskatchewan compared to those previously established that relied solely on bare soil composite imagery.

Dissolved inorganic carbon export from rivers of Great Britain: Spatial distribution and potential catchment-scale controls

Dissolved inorganic carbon (DIC) fluxes from the land to ocean have been quantified for many rivers globally. However, CO2 fluxes to the atmosphere from inland waters are quantitatively significant components of the global carbon cycle that are currently poorly constrained. Understanding, the relative contributions of natural and human-impacted processes on the DIC cycle within catchments may provide a basis for developing improved management strategies to mitigate free CO2 concentrations in rivers and subsequent evasion to the atmosphere. Here, a large, internally consistent dataset collected from 41 catchments across Great Britain (GB), accounting for ∼36% of land area (∼83,997 km2) and representative of national land cover, was used to investigate catchment controls on riverine dissolved inorganic carbon (DIC), bicarbonate (HCO3−) and free CO2 concentrations, fluxes to the coastal sea and annual yields per unit area of catchment. Estimated DIC flux to sea for the survey catchments was 647 kt DIC yr−1 which represented 69% of the total dissolved carbon flux from these catchments. Generally, those catchments with large proportions of carbonate and sedimentary sandstone were found to deliver greater DIC and HCO3− to the ocean. The calculated mean free CO2 yield for survey catchments (i.e. potential CO2 emission to the atmosphere) was 0.56 t C km−2 yr−1. Regression models demonstrated that whilst river DIC (R2 = 0.77) and HCO3− (R2 = 0.77) concentrations are largely explained by the geology of the landmass, along with a negative correlation to annual precipitation, free CO2 concentrations were strongly linked to catchment macronutrient status. Overall, DIC dominates dissolved C inputs to coastal waters, meaning that estuarine carbon dynamics are sensitive to underlying geology and therefore are likely to be reasonably constant. In contrast, potential losses of carbon to the atmosphere via dissolved CO2, which likely constitute a significant fraction of net terrestrial ecosystem production and hence the national carbon budget, may be amenable to greater direct management via altering patterns of land use.

Mineral Carbonation of Basic Oxygen Furnace Slags

Mineral carbonation is a method in carbon capture and utilization (CCU) in which carbon dioxide reacts with natural or synthetic mineral phases to form carbonates. In this study, BOF slag consisting of alite, Ca3SiO5, belite, Ca2SiO4, melilite, (Ca,Na)2(Mg,Al)[4][Si2O7], brownmillerite, Ca(Fe,Al)2O5, calcium ferrite, Ca2FeO4 and Ca-, Mg- and Mn-bearing wuestite, (Mg,Ca,Mn,Fe)O, was crushed into different particle size fractions and exposed over various durations (1 d, 3 d, 9 d, 14 d, 24 d) at a grate to 120 °C hot off-gas with a CO2 content of 25%. However, the total inorganic carbon (TIC) content never increases above the detection limit of 0.5% throughout the experimental duration. The determination of the carbonation depth using phenolphthalein does not reveal a homogeneous carbonation front, but an irregular carbonation. This observation was confirmed by microprobe analyses using elemental mapping. The solubility of the slag increases with increasing carbonation, e.g., the leachability of sulfate increases from 7.8 to 8270 mg/kg dry matter (DM), and of calcium from 940 to 3860 mg/kg DM. The leaching of environmentally relevant element varies: the leachable concentration of molybdenum increases from 0.017 mg/kg DM to 0.089 mg/kg DM, that of chromium remains constant (ca. 0.05 mg/kg DM) whereas that of vanadium decreases from 1.1 to 0.45 mg/kg. In summary, the chosen carbonation technology must be improved to enhance carbonate yield.

Nano-scale analysis of uranium release behavior from river sediment in the Ili basin

Due to the limitations of the conventional water sample pretreatment methods, some of the colloidal uranium (U) has long been misidentified as "dissolved" phase. In this work, the U species in river water in the Ili Basin was classified into submicron-colloidal (0.1–1 μm), nano-colloidal (0.1 μm–3 kDa) and dissolved phases (< 3 kDa) by using high-speed centrifugation and ultrafiltration. The U concentration in the river water was 5.39–8.75 μg/L, which was dominated by nano-colloidal phase (55–70%). The nano-colloidal particles were mainly composed of particulate organic matter (POM) and had a very high adsorption capacity for U (accounting for 70 ± 23% of colloidal U). Sediment disturbance, low temperature, and high inorganic carbon greatly improved the release of nano-colloidal U, but high levels of Ca2+ inhibited it. The simulated river experiments indicated that the flow regime determined the release of nano-colloidal U, and large amounts of nano-colloidal U might be released during spring floods in the Ili basin. Moreover, global warming increases river flow and inorganic carbon content, which may greatly promote the release and migration of nano-colloidal U.