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Carbon dioxide removal (CDR) strategies like enhanced weathering and river/ocean alkalinity enhancement have been suggested to increase alkalinity in rivers, coastal areas, and eventually oceans. The effectiveness and sustainability of these CDR approaches depend on the persistence of added alkalinity, since exceeding certain Ω-thresholds for a given water composition may lead to carbonates formation, causing the loss of previously added alkalinity. In this research, stability of alkalinity was tested using incubation experiments with Elbe estuary freshwater from two seasons (March and August). Alkalinity was increased up to 4000 μmol kgw−1, with varying salinity from 0 to 16. This study shows that the stability of alkalinity depends on the presence and quantity of suspended particles, seasonality of water chemistry, and salinity. Based on the experimental data, the Elbe estuary may take up additional alkalinity in the freshwater part, corresponding to ∼3.0 MtCO2 yr−1 being transported towards the North Sea. Estimates of alkalinity additions from the 1970s to 2010s show a decreasing potential due to changes in pCO2 and pH. The upper geochemical limit for transporting additional alkalinity through estuarine systems serves as a critical boundary. Environmentally feasible levels may be lower than identified here and depend on environmental regulations.

Aim We studied global variation in beta diversity patterns of lake macrophytes using regional data from across the world. Specifically, we examined (1) how beta diversity of aquatic macrophytes is partitioned between species turnover and nestedness within each study region, and (2) which environmental characteristics structure variation in these beta diversity components. Location Global. Methods We used presence–absence data for aquatic macrophytes from 21 regions distributed around the world. We calculated pairwise-site and multiple-site beta diversity among lakes within each region using Sørensen dissimilarity index and partitioned it into turnover and nestedness coefficients. Beta regression was used to correlate the diversity coefficients with regional environmental characteristics. Results Aquatic macrophytes showed different levels of beta diversity within each of the 21 study regions, with species turnover typically accounting for the majority of beta diversity, especially in high-diversity regions. However, nestedness contributed 30–50% of total variation in macrophyte beta diversity in low-diversity regions. The most important environmental factor explaining the three beta diversity coefficients (total, species turnover and nestedness) was elevation range, followed by relative areal extent of freshwater, latitude and water alkalinity range. Main conclusions Our findings show that global patterns in beta diversity of lake macrophytes are caused by species turnover rather than by nestedness. These patterns in beta diversity were driven by natural environmental heterogeneity, notably variability in elevation range (also related to temperature variation) among regions. In addition, a greater range in alkalinity within a region, likely amplified by human activities, was also correlated with increased macrophyte beta diversity. These findings suggest that efforts to conserve aquatic macrophyte diversity should primarily focus on regions with large numbers of lakes that exhibit broad environmental gradients.

Bauxite residue is a highly alkaline material generated from the production of alumina in which bauxite is dissolved in caustic soda. Approximately 4.4 billion tons of bauxite residues are either stockpiled or landfilled, creating environmental risks either from the generation of dust or migration of filtrates. High alkalinity is the critical factor restricting complete utilization of bauxite residues, whilst the application of alkaline regulation agents is costly and difficult to apply widely. For now, current industrial wastes, such as waste acid, ammonia nitrogen wastewater, waste gypsum and biomass, have become major problems restricting the development of the social economy. Regulation of bauxite residues alkalinity by industrial waste was proposed to achieve ‘waste control by waste’ with good economic and ecological benefits. This review will focus on the origin and transformation of alkalinity in bauxite residues using typical industrial waste. It will propose key research directions with an emphasis on alkaline regulation by industrial waste, whilst also providing a scientific reference point for their potential use as amendments to enhance soil formation and establish vegetation on bauxite residue disposal areas (BRDAs) following large-scale disposal.

Macroalgal ecosystems remain underrepresented in blue carbon frameworks, largely due to uncertainties surrounding the fate of macroalgal carbon during decomposition. Laboratory experiments on Sargassum horneri, Codium fragile, and Ulva australis revealed concurrent increases in total alkalinity and dissolved inorganic carbon, indicating substantial bicarbonate (HCO3−) production via previously unrecognized mechanisms in oxygenated environments. This pattern was corroborated by field data from Korean coastal macroalgal habitats and Yellow Sea macroalgal blooms. Contrary to the conventional view that macroalgal decomposition primarily releases CO2, over half of the inorganic carbon is released as HCO3− in oxygenated waters. This bicarbonate surge—potentially driven by sulfate reduction in anoxic macroalgal aggregates or intracellular HCO3− release—not only raises seawater alkalinity but also enhances carbon sequestration potential and mitigates ocean acidification. These findings highlight the critical role of macroalgal habitats in the global carbon cycle and call for their inclusion in blue carbon strategies.

Oceanic dissolved inorganic carbon (TC) is the largest pool of carbon that substantially interacts with the atmosphere on human timescales. Oceanic TC is increasing through uptake of anthropogenic carbon dioxide (CO2), and seawater pH is decreasing as a consequence. Both the exchange of CO2 between the ocean and atmosphere and the pH response are governed by a set of parameters that interact through chemical equilibria, collectively known as the marine carbonate system. To investigate these processes, at least two of the marine carbonate system's parameters are typically measured – most commonly, two from TC, total alkalinity (AT), pH, and seawater CO2 fugacity (fCO2; or its partial pressure, pCO2, or its dry-air mole fraction, xCO2) – from which the remaining parameters can be calculated and the equilibrium state of seawater solved. Several software tools exist to carry out these calculations, but no fully functional and rigorously validated tool written in Python, a popular scientific programming language, was previously available. Here, we present PyCO2SYS, a Python package intended to fill this capability gap. We describe the elements of PyCO2SYS that have been inherited from the existing CO2SYS family of software and explain subsequent adjustments and improvements. For example, PyCO2SYS uses automatic differentiation to solve the marine carbonate system and calculate chemical buffer factors, ensuring that the effect of every modelled solute and reaction is accurately included in all its results. We validate PyCO2SYS with internal consistency tests and comparisons against other software, showing that PyCO2SYS produces results that are either virtually identical or different for known reasons, with the differences negligible for all practical purposes. We discuss insights that guided the development of PyCO2SYS: for example, the fact that the marine carbonate system cannot be unambiguously solved from certain pairs of parameters. Finally, we consider potential future developments to PyCO2SYS and discuss the outlook for this and other software for solving the marine carbonate system. The code for PyCO2SYS is distributed via GitHub (https://github.com/mvdh7/PyCO2SYS, last access: 23 December 2021) under the GNU General Public License v3, archived on Zenodo , and documented online (https://pyco2sys.readthedocs.io/en/latest/, last access: 23 December 2021).

Ocean alkalinity enhancement (OAE) has the potential to mitigate ocean acidification (OA) and induce atmospheric carbon dioxide (CO2) removal (CDR). We evaluate the CDR and OA mitigation impacts of a sustained point‐source OAE of 1.67 × 1010 mol total alkalinity (TA) yr−1 (equivalent to 667,950 metric tons NaOH yr−1) in Unimak Pass, Alaska. We find the alkalinity elevation initially mitigates OA by decreasing pCO2 and increasing aragonite saturation state and pH. Then, enhanced air‐to‐sea CO2 exchange follows with an approximate e‐folding time scale of 5 weeks. Meaningful modeled OA mitigation with reductions of >10 μatm pCO2 (or just under 0.02 pH units) extends 100–100,000 km2 around the TA addition site. The CDR efficiency (i.e., the experimental seawater dissolved inorganic carbon (DIC) increase divided by the maximum DIC increase expected from the added TA) after the first 3 years is 0.96 ± 0.01, reflecting essentially complete air‐sea CO2 adjustment to the additional TA. This high efficiency is potentially a unique feature of the Bering Sea related to the shallow depths and mixed layer depths. The ratio of DIC increase to the TA added is also high (≥0.85) due to the high dissolved carbon content of seawater in the Bering Sea. The air‐sea gas exchange adjustment requires 3.6 months to become (>95%) complete, so the signal in dissolved carbon concentrations will likely be undetectable amid natural variability after dilution by ocean mixing. We therefore argue that modeling, on a range of scales, will need to play a major role in assessing the impacts of OAE interventions. Plain Language Summary The Intergovernmental Panel on Climate Change suggests that carbon dioxide (CO2) removal (CDR) approaches will be required to stabilize the global temperature increase at 1.5–2°C. In this study, we simulated the climate mitigation impacts of adding alkalinity (equivalent to 667,950 metric ton NaOH yr−1) in Unimak Pass on the southern boundary of the Bering Sea. We found that adding alkalinity can accelerate the ocean CO2 uptake and storage and mitigate ocean acidification near the alkalinity addition. It takes about 3.6 months for the Ocean alkalinity enhancement impacted area to take up the extra CO2. The naturally cold and carbon rich water in the Bering Sea and the tendency of Bering Sea surface waters to linger near the ocean surface without mixing into the subsurface ocean both lead to high CDR efficiencies (>96%) from alkalinity additions in the Bering Sea. However, even with high efficiency, it would take >8,000 alkalinity additions of the kind we simulated to be operating by the year 2100 to meet the target to stabilize global temperatures within the targeted range. Key Points We used regional ocean model to simulate single point‐source ocean alkalinity enhancement in the Bering Sea The steady state carbon dioxide removal efficiency was near one in years 3+ of the simulation The meaningful modeled ocean acidification mitigation is confined to the region near the alkalinity addition

Groundwater quality of Gulbarga District is extensively monitored for two years of study period from October 1999 to September 2001. Twenty-five different sampling stations were selected for the study purpose in the city and five selected villages in the district. Gulbarga districts lies in the northern plains of Karnataka State, covers an area of 16,244km super(2) and lies between 16-11' and 17-19'N latitude and 76-54'E longitude The study revealed that the water sources in the area are heavily polluted. The major water quality parameters exceeding the permissible limits during all the seasons are total hardness, calcium hardness, magnesium hardness, alkalinity and MPN (Bacterial count) and other parameters have shown distinctive variation in different stations and season. Most of these parameters are correlated with one another. Statistical analysis of the data is presented.

Salinity-alkalinity stress has caused severe environment problems that negatively impact the growth and development of watermelon ( L.). In this study, watermelon seedlings were inoculated with the arbuscular mycorrhizal fungi (AMF) to investigate its effect on watermelon growth and development. The main measurements included morphological traits, elemental and water uptake, the level of reactive oxygen species, antioxidant enzyme and photosynthesis activities, and relative expression levels of stress response genes. Under salinity-alkalinity stresses, watermelon morphological traits, elemental and water uptake were all significantly alleviated after incubation with AMF. Antioxidant abilities of watermelon were significantly improved after incubation with AMF in salinity-alkalinity stresses. Under normal conditions, all photosynthesis related parameters were significantly increased after incubation of AMF. In contrast, they were all significantly reduced under salinity-alkalinity stresses and were all significantly alleviated after incubation of AMF. Salinity-alkalinity stresses impacted the chloroplast structure and AMF significantly alleviated these damages. Under salinity-alkalinity stresses, the relative expression level of was significantly reduced and was significantly alleviated after AMF treatment. The relative expression level of was significantly increased and was further significantly reduced after AMF treatment. For the relative expression levels of antioxidant response related genes , their relative expression levels were significantly increased and were further significantly increased after AMF treatment. Our study demonstrated the beneficial effects of AMF under salinity-alkalinity stresses, which could be implicated in the management of watermelon cultivation under salinity-alkalinity regions.

Background Salinity-alkalinity stress is one of the major abiotic stresses affecting plant growth and development. γ-Aminobutyrate (GABA) is a non-protein amino acid that functions in stress tolerance. However, the interactions between cellular redox signaling and chlorophyll (Chl) metabolism involved in GABA-induced salinity-alkalinity stress tolerance in plants remains largely unknown. Here, we investigated the role of GABA in perceiving and regulating chlorophyll biosynthesis and oxidative stress induced by salinity-alkalinity stress in muskmelon leaves. We also evaluated the effects of hydrogen peroxide (H 2 O 2 ), glutathione (GSH), and ascorbate (AsA) on GABA-induced salinity-alkalinity stress tolerance. Results Salinity-alkalinity stress increased malondialdehyde (MDA) content, relative electrical conductivity (REC), and the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and dehydroascorbate reductase (DHAR). Salinity-alkalinity stress decreased shoot dry and fresh weight and leaf area, reduced glutathione and ascorbate (GSH and AsA) contents, activities of glutathione reductase (GR) and monodehydroascorbate reductase (MDAR). By contrast, pretreatment with GABA, H 2 O 2 , GSH, or AsA significantly inhibited these salinity-alkalinity stress-induced effects. The ability of GABA to relieve salinity-alkalinity stress was significantly reduced when the production of endogenous H 2 O 2 was inhibited, but was not affected by inhibiting endogenous AsA and GSH production. Exogenous GABA induced respiratory burst oxidase homologue D ( RBOHD ) genes expression and H 2 O 2 accumulation under normal conditions but reduced the H 2 O 2 content under salinity-alkalinity stress. Salinity-alkalinity stress increased the accumulation of the chlorophyll synthesis precursors glutamate (Glu), δ-aminolevulinic acid (ALA), porphobilinogen (PBG), uroporphyrinogen III (URO III), Mg-protoporphyrin IX (Mg-proto IX), protoporphyrin IX (Proto IX), protochlorophyll (Pchl), thereby increasing the Chl content. Under salinity-alkalinity stress, exogenous GABA increased ALA content, but reduced the contents of Glu, PBG, URO III, Mg-proto IX, Proto IX, Pchl, and Chl. However, salinity-alkalinity stress or GABA treated plant genes expression involved in Chl synthesis had no consistent trends with Chl precursor contents. Conclusions Exogenous GABA elevated H 2 O 2 may act as a signal molecule, while AsA and GSH function as antioxidants, in GABA-induced salinity-alkalinity tolerance. These factors maintain membrane integrity which was essential for the ordered chlorophyll biosynthesis. Pretreatment with exogenous GABA mitigated salinity-alkalinity stress caused excessive accumulation of Chl and its precursors, to avoid photooxidation injury.

Hydrogen peroxide photosynthesis suffers from insufficient catalytic activity due to the high energy barrier of hydrogen extraction from H 2 O. Herein, we report that mechanochemically synthesized keto-form anthraquinone covalent organic framework which is able to directly synthesize H 2 O 2 (4784 μmol h −1 g −1 at λ > 400 nm) from oxygen and alkaline water (pH = 13) in the absence of any sacrificial reagents. The strong alkalinity resulted in the formation of OH - (H 2 O) n clusters in water, which were adsorbed on keto moieties within the framework and then dissociated into O 2 and active hydrogen, because the energy barrier of hydrogen extraction was largely lowered. The produced hydrogen reacted with anthraquinone to generate anthrahydroquinone, which was subsequently oxidized by O 2 to produce H 2 O 2 . This study ultimately sheds light on the importance of hydrogen extraction from H 2 O for H 2 O 2 photosynthesis and demonstrates that H 2 O 2 synthesis is achievable under alkaline conditions. Hydrogen peroxide photosynthesis is an important reaction that suffers from poor activity due to the high energy barrier of hydrogen extraction in water. Here, we report a keto-form anthraquinone framework that shows promising performance in alkaline conditions.