Acid Deposition Research Articles

Mitigating low-temperature corrosion in flue-gas heat exchangers for improving thermal storage efficiency in geothermal power plants

Geothermal energy is a renewable and stable energy source that plays a crucial role in providing heat. However, underground sulfur fumes have been restricting the heat exchange and storage rate for years. Accurately predicting the condensation of acidic substances of flue gas heat exchangers is crucial in geothermal heat storage. In this paper, Acid and water vapor have been firstly utilized to forecast the deposition of acidic substances on the heat exchanger’s surface. Utilizing gas–liquid equilibrium data of H2SO4-H2O solution and multi-component transport theory, a numerical model has been developed to analyze the impact of acidic deposition and corrosion characteristics. The results shown a correlation between the distribution of acidic substances deposition within heat exchanger and temperature distribution. When water vapor volume fraction increased from 3 % to 18 %, there was a corresponding increase of acid condensation rate on surface. Specifically, the condensation rate increased by 9.6 %, 16.1 %, and 21.8 % respectively under the flow rates of 5 m/s, 8 m/s, and 10 m/s, while the acid mass fraction decreased by 22.4 %, 20.7 %, and 20.1 % respectively. Acidic substances predominantly deposit in specific areas of the heat exchanger. Moreover, Water vapor content increasing can lead to reduction deposition of acidic substances, this may be a potential method to reduce loss of heat exchanger and increase heat storage. These findings offer a significant step forward heat exchanger technology and geothermal energy application.

Acid rain prediction in the Guangdong-Hong Kong-Macao Greater Bay Area using an explainable machine learning framework

Acid rain, characterized by pH values lower than 5.6, is a critical natural disturbance of ecosystems, which threatens the sustainability of ecosystems, agriculture, and human society worldwide. However, accurately quantifying the driving factors of acid rain remains challenging due to a changing environment of significant spatial heterogeneity. Here, we established an explainable machine-learning framework (MLF) using 19 meteorological, air pollutant, and land surface variables as model input to construct the pH values of acid rain across the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) during 2006–2021. The MLF includes Extreme Gradient Boosting (XGBoost) for acid deposition prediction and a SHapley Additive exPlanations method (SHAP) for interpreting factor importance. The results indicated that the observed increases in pH values of acid rain are predominantly controlled by the significant decreases in maximum daily sulfur dioxide (SO2) concentration of air across GBA, with its relative contribution ranging from 16.2% to 31.9% for each city. Changes in the urbanization rate and the proximity to the coast also play significant roles in predicting the pH values of acid rain. Meteorological variables typically have minimal impact on acid rain predictions, with their contribution generally being less than 5%, indicating the complex physical process of acid rain generation. This study enhanced our comprehension of the spatial variability of acid rain drivers across a highly developed region, providing valuable insights and case studies for regions worldwide that frequently experience acid rain.

Intraspecific Trait Variation Regulates Biodiversity and Community Productivity of Shrublands in Drylands

Intraspecific variation (Intra-V) has played an important role in determining the responses of ecosystem functions to climate change. However, its specific role in the regulation of ecosystem functions during community assembly is less investigated. In this study, we conducted a transect survey in northwest China and determined different plant functional types, namely resource-conservative, medium, and resource-acquisitive strategies, which describe resource-use strategies of plants in multi-functional dimensions. Plant functional traits including canopy, wood density (WD), height, specific leaf area (SLA), and leaf nitrogen (N) and phosphorus (P) concentrations were determined. Ecological filters, including external filtering (assembly processes at the regional scale), internal filtering (assembly processes within a certain community), and functional redundancy, were employed to examine plant environment interactions. We found that with the decrease in environmental pressure, dominant shrub plants changed from conservative to acquisition species in drylands. Specifically, a benign environment (such as stable and adequate precipitation, loose soil, and increased acid deposition) significantly increased plant mean traits, such as SLA and WD of shrubs, especially for conservative strategy plants. In addition, a benign environment mainly reduced the functional redundancy of SLA (FRedSLA) by strengthening internal filtering and, ultimately, increased aboveground biomass but decreased species richness. Our results suggest that conservative strategy plants with stronger adaptability to the external environment may exhibit more competitive advantages and play a more important role in community construction under future climate scenarios of gradual warming and wetting in northwest China. Our results also revealed that trait-based Intra-V may be a more reasonable ecological filter than plant mean traits for predicting the structure and function of dryland ecosystems.

Dietary Threonine Promoted the Growth and Ovarian Development of the Red Swamp Crayfish (Procambarus clarkii)

To explore the effects of dietary threonine on growth and ovarian development of red swamp crayfish (Procambarus clarkii), crayfish (5.48 ± 0.19 g) were fed six isoproteic and isoenergetic diets with varying levels of threonine (7.16 g/kg (control), 9.19, 12.74, 16.44, 20.83, and 23.78 g/kg) for 8 weeks. The results showed that weight gain rate, feed conversion ratio, protein efficiency rate, protein deposition rate, and essential amino acid deposition rates obtained the optimal values when the dietary threonine level was 12.74 or 16.44 g/kg. Compared to the control group, the 12.74 g/kg group exhibited enhanced nonspecific immunity and antioxidant properties. The 16.44 g/kg group demonstrated a significant increase in the frequency of B cells and R cells in the hepatopancreas, the length and width of intestinal villi, and the activities of protease and lipase. It also showed elevated ecdysterone hormone, gonadal index (GI), cAMP content, and the relative abundance of beneficial intestinal microflora. Compared to the control group, the mRNA expression of mTOR, S6K1, 4EBP1, EcR, RXR, chitinase, PKA, Vg, cdc2, and cyclin B was significantly upregulated, and the mRNA expression of MIH was significantly downregulated in the 16.44 g/kg group. Overall, optimal dietary threonine could improve intestinal health, regulate immune function, and enhance protein utilization, molting, and growth performance of red swamp crayfish. Additionally, it improved the synthesis of yolk substance and facilitated the development of ovarian cells of female crayfish. The optimal threonine level was 14.87–16.94 g/kg (dry matter), corresponding to 42.51–48.42 g/kg of dietary protein in red swamp crayfish.

Quarter century of mercury litterfall at a coniferous forest responding to climate change, Central Europe.

This work evaluated the 25-year-long trends (1994-2018) in mercury (Hg) concentrations and fluxes in spruce litterfall at a forest research plot Načetín (NAC) recovering from acidic deposition in the Ore Mountains, Czech Republic. The mean litterfall Hg deposition averaged 51 ± 18µgm-2year-1, which has been the highest litterfall Hg deposition reported up to date on the European continent. In contrast, the wet deposition (2017-2019) was an order of magnitude lower averaging at 2.5 ± 1.5µgm-2year-1. All the spruce litterfall components bark, twigs, needles, cones, and a mixture of unidentified fragments had elevated mean Hg concentrations relative to background sites averaging 256 ± 77, 234 ± 62, 119 ± 23, 95 ± 14, and 44 ± 15µg kg-1, respectively. Elevated litterfall Hg deposition and concentrations were attributed to the nearby local Hg emission source-coal-fired power plants. Temporally, the decrease of Czech Hg emissions since the 1990s was reflected by the decreasing trend of Hg concentrations in litterfall bark, cones, and twigs, while in needles and other material, Hg increased but insignificantly. Total litterfall ratios of Hg/C, Hg/N, and Hg/S were lower than those in soil O horizons averaging at 0.23 ± 0.04, 9.5 ± 2.0, and 170 ± 37μgg-1, respectively. Since the beginning of monitoring, total litterfall Hg/C exhibited no trend, Hg/N decreased, and Hg/S increased. The litterfall biomass deposition averaging at 469 ± 176gm-2year-1 increased through time resulting in an increased Hg litterfall deposition at NAC by 1.1µgm-2year-1 despite the decreases in Czech Hg emissions. Peaks of annual litterfall Hg deposition up to 96µgm-2year-1 at NAC during the 25years of monitoring resulted from weather extremes such as rime-snow accumulation, wind gusts, droughts, and insect infestation, which all significantly affected the annual biomass deposition. Based on our observations, further increases in biomass and litterfall Hg deposition rates can be expected due to the onset of bark beetle infestation and the increasing number of droughts caused by climate change.

Metabolic effects of phospholipids extracted from capelin (Mallotus villosus) roe on HepG2 cells

This study aimed to evaluate the effects of capelin roe phospholipid (CPL) on lipid accumulation, fatty acid profile, oxidative stress, and changes in target macromolecular structure in HepG2 cells using multidimensional hyperspectral technique. The results showed that CPL significantly inhibited oleic acid-induced accumulation of intracellular lipids and increased the activity of intracellular antioxidant enzymes (CAT, GSH-Px, SOD). The control and CPL-treated groups promoted accumulation of unsaturated fatty acids and reduced deposition of saturated fatty acids. The therapeutic effects of CPL positively correlated with its concentration. Fourier transform infrared spectroscopy and two-dimensional correlation infrared analysis indicated that CPL decreased the relative contents of intracellular carbohydrate, nucleic acid, –CH2-, and ν(C=O)/νas (CH2+CH3), and maintained the order of intracellular protein structure. Fourier transform infrared spectroscopy could be used for label-free cell sorting. This work provided a direction for the subsequent development of functional lipids in aquaculture.

Metabolic-Dysfunction Associated Liver Disease Progresses Independent of Weight in a Rodent Model

Background: Metabolic dysfunction associated steatotic liver disease (MASLD) is the most prevalent liver disease worldwide with an estimated 25% of U.S. adults having MASLD. MASLD is typically regarded as a diet driven disease, with the Western diet (high fat, high sugar, low fiber) being a major driver. Recently, evidence suggests MASLD can be present regardless of body weight. There is not good evidence on how prevalent this is, but reports suggest it could be as high as nearly 30% of MASLD patients. As such, there is a critical need to better understand MASLD independent of weight to ensure all individuals with the disease are receiving proper diagnosis and treatment. Methods: Young female rats were fed either a Control (AIN-93G) or Western (45% fat, 34% sugar) diet for 8 weeks. Histology, RT-qPCR, and standard biological assays were performed to analyze differences in hepatic function and fatty acid analysis was used to analyze fatty acid deposition in the liver, adipose tissue, and brain. Results: There were no statistically significant differences in the weights of rats consuming a Control or Western diet. However, consuming a Western diet had increased histological evidence of fat deposition and inflammation compared to Control. Rats consuming a Western diet also displayed increased ( p<0.05) hepatic triglyceride content and relative expression of several key genes involved in lipogenesis and oxidative stress. Fatty acid analysis found Western diet rats to have increased (p<0.05) hepatic monounsaturated fatty acid (MUFA) content, while adipose tissue of those same animals had decreased (p<0.05) MUFAs. Conclusions: The Western diet plays a significant role in the development of MASLD independent of differences in weight. This model may serve to better elucidate mechanisms at play in lean MASLD. We are currently conducting additional experiments on the role of alcohol in this phenomenon. WVU Davis College Dean's Opportunity Fund and the UVM Food Systems Research Center. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Hydrochemical fingerprints of karst underground river systems impacted by urbanization in Guiyang, Southwest China

Karst groundwater plays an irreplaceable role in the formation and development of urban areas, and land-use and land-cover change (LUCC) and the input of pollutants during the urbanization process would pose potential environmental risks to underground rivers. We analysed the relationship between urbanization processes and underground river hydrochemistry over nearly 35 years in Guiyang city, southwest of China, it was found that concentrations of various cations and anions, as well as total dissolved solids (TDS), gradually increased with the urbanization process, with significant fluctuations during the rapid urbanization periods. The Hydrochemical Facies Evolution Diagram (HFED) clearly showed the influence of urbanization on the hydrochemistry of the underground rivers. The ion ratios of γMg2+/γCa2+—γHCO3−, γNa+/γCl−, Ca2+/Mg2+—Ca2+ or Mg2+/Σ cations, HCO3−/SO42−—HCO3− or SO42−/Σ anions revealed two distinct phases in the hydrochemical evolution of the underground river system, highly consistent with the urbanization process. Before the rapid urbanization, acid deposition and agricultural activities affected the hydrochemistry, with HCO3-Ca·Mg and HCO3·SO4-Ca·Mg as the dominant types controlled by limestone and dolomite dissolution in water-rock interactions. As acid deposition diminished, the input of SO42− from urban sewage compensated for the reduced impact, but the increased impermeable surfaces reduced the infiltration of atmospheric precipitation, leading to a reduced dissolution of dolomite minerals in water-rock interactions, resulting in a decrease in Mg2+ and a change in the hydrochemical type. The hydrochemical type evolved from a single HCO3·SO4-Ca·Mg type and HCO3-Ca·Mg type to multiple types, such as HCO3·Cl-Ca, HCO3·SO4-Ca, HCO3-Ca, and HCO3·SO4-Ca·Mg, and was highly unstable. With changes in land use, the proportions of various cations and anions in the hydrochemistry changed, especially NH4+, NO3−, SO42−, Na+, and Cl−, which were more sensitive to human activities. This study indicated the impact of urbanization on the hydrochemistry of the underground river system, with the input of SO42− from human activities and the increase in paved surfaces due to urbanization collectively altering the hydrochemical types of the underground river system. The rapid response of karst underground river system hydrochemistry indicates a potential impact on groundwater system by urbanization that should not be ignored.

Potential Strategy to Control the Organic Components of Condensable Particulate Matter: A Critical Review.

More and more attention has been paid to condensable particulate matter (CPM) since its emissions have surpassed that of filterable particulate matter (FPM) with the large-scale application of ultralow-emission reform. CPM is a gaseous material in the flue stack but instantly turns into particles after leaving the stack. It is composed of inorganic and organic components. Organic components are an important part of CPM, and they are an irritant, teratogenic, and carcinogenic, which triggers photochemical smog, urban haze, and acid deposition. CPM organic components can aggravate air pollution and climate change; therefore, consideration should be given to them. Based on existing methods for removing atmospheric organic pollutants and combined with the characteristics of CPM organic components, we provide a critical overview from the aspects of (i) fundamental cognition of CPM, (ii) common methods to control CPM organic components, and (iii) catalytic oxidation of CPM organic components. As one of the most encouraging methods, catalytic oxidation is discussed in detail, especially in combination with selective catalytic reduction (SCR) technology, to meet the growing demands for multipollutant control (MPC). We believe that this review is inspiring for a fuller understanding and deeper exploration of promising approaches to control CPM organic components.

The cooperative regulatory effect of the miRNA-130 family on milk fat metabolism in dairy cows.

There is a strong relationship between the content of beneficial fatty acids in milk and milk fat metabolic activity in the mammary gland. To improve milk quality, it is therefore necessary to study fatty acid metabolism in bovine mammary gland tissue. In adipose tissue, peroxisome proliferator-activated receptor gamma (PPARG), the core transcription factor, regulates the fatty acid metabolism gene network and determines fatty acid deposition. However, its regulatory effects on mammary gland fatty acid metabolism during lactation have rarely been reported. Transcriptome sequencing was performed during the prelactation period and the peak lactation period to examine mRNA expression. The significant upregulation of PPARG drew our attention and led us to conduct further research. According to bioinformatics prediction, dual-luciferase reporter system detection, real-time quantitative reverse transcription polymerase chain reaction and Western blotting, miR-130a and miR-130b could directly target PPARG and inhibit its expression. Furthermore, triglyceride and oil red O staining proved that miR-130a and miR-130b inhibited milk fat metabolism in bovine mammary epithelial cells (BMECs), while PPARG promoted this metabolism. In addition, we also found that the coexpression of miR-130a and miR-130b significantly enhanced their ability to regulate milk fat metabolism. In conclusion, our findings indicated that miR-130a and miR-130b could target and repress PPARG and that they also have a functional superposition effect. miR-130a and miR-130b seem to synergistically regulate lipid catabolism via the control of PPARG in BMECs. In the long-term, these findings might be helpful in developing practical means to improve high-quality milk.

E046 Lytic lesions; metastatic disease or gout?

Abstract Background/Aims Uric acid crystal deposition in the spine is uncommonly diagnosed, although the frequency of axial involvement is thought to be as high as 14-35%. Studies have shown that spinal gout is more common in men aged 35-75 years, with a history of chronic polyarticular tophaceous gout which is not optimally controlled being a key risk factor. Recent studies have shown that spinal gout is under and misdiagnosed due to its non-specific presentation of back pain or absence of symptoms. Our case report exemplifies this diagnostic challenge. Methods In this report we describe a case of a 79-year-old male with a history of polyarticular tophaceous gout, chronic kidney disease and previous renal carcinoma treated with curative radiotherapy. He presented with a 4-week history of progressive exertional dyspnoea and orthopnoea. He was commenced on intravenous diuretics which lead to an acute kidney injury, with his eGFR dropping to 14mL/min. His preadmission allopurinol and colchicine were held and clinically he developed a flare of gout affecting his right wrist and right second and third MCP joints. A CT scan of his abdomen and pelvis, carried out to investigate potential bowel obstruction, showed no evidence of obstruction but it did reveal multiple lytic lesions in the spine with potential extension into the spinal canal at T9 and L5. He did not have any back pain and his neurological examination was normal. Results A working diagnosis of spinal metastasis with potential cord compression was made and the patient was commenced on high dose steroids. He subsequently underwent an MRI whole spine which showed marrow abnormalities and destructive soft tissues changes affecting various facet joints in the thoracic and lumbar spine. The primary differential remained metastases but due to the unusual distribution of the marrow changes in which the vertebral bodies were completely spared, the initial CT images were reviewed on spectral scanning which demonstrated uric acid deposition in the affected facet joints. The diagnosis was confirmed as gout in the spine when a PET-CT scan revealed no potential primary source of malignancy. The gout flare in his hand settled with the steroids prescribed to treat the potential cord compression and he continued to deny suffering from back pain. Conclusion A literature search demonstrates that reports of spinal gout being described as lytic lesions on CT are rare. Spinal gout should be considered as a differential in a patient with facet joint lytic lesions on imaging, without involvement of the vertebral body and where no primary malignancy is found. Our case demonstrates how dual energy CT scanning can prevent the need for invasive biopsy in cases of diagnostic uncertainty in patients with a history of poorly controlled chronic tophaceous gout. Disclosure S.K. Stewart: None. D.J. Coulter: None. C. Masih: None.

Changes in microbial composition explain the contrasting responses of glucose and lignin decomposition to soil acidification in an alpine grassland

Soil acidification often suppresses microbial growth and activities, resulting in a negative impact on soil organic carbon (C) decomposition. While the detrimental effects of acidification on soil and plant properties have been extensively studied, less attention has been paid on the shifts in soil microbial communities and their influences of the decomposition of organic C with different chemical complexities. Taking advantage of an acid addition experiment in a Tibetan alpine meadow, here we examined the response of soil microbial communities to soil acidification and microbial effect on the decomposition of organic C with different chemical complexities (i.e., glucose and lignin, representing labile and recalcitrant C respectively). We found that soil acidification had no impact on microbial respiration and microbial abundance even though it decreased bacterial diversity significantly. Soil acidification increased the relative abundance of some microbial taxa, like Alphaproteobacteria and Acidobacteriia in bacteria increased by 36 %, 284 %, and Eurotiomycetes, Sordariomycetes and Leotiomycetes in fungi increased by 145 %, 279 % and 12.7-fold, but decreased the relative abundance of Acidimicrobiia by 33 % in highest acid addition treatment. Changes in microbial communities (bacterial and fungal community composition, the diversity of bacterial community and the ratio of fungi to bacteria) are significantly related to the decomposition of glucose and lignin. More specifically, soil acidification decreased the decomposition of glucose but increased the decomposition of lignin, indicating a trade-off between the decomposition of labile and recalcitrant soil organic C under soil acidification. Overall, shifts in microbial communities under soil acidification might be accompanied by an increased ability to break down more recalcitrant C. This trade-off between the decomposition of labile and recalcitrant C may change soil C quality under future acid deposition scenarios.

Performance of the one-part geopolymer stabilized soft clay under acids attack

The evolution of globalization and rapid industrialization, coupled with intensive human activities, leads to a significant release of acidic gases and particles (e.g., NOX and SO2) is unavoidable. These emissions eventually result in dry and wet acid depositions due to atmospheric circulation. This infiltration of acidic elements alters the chemical properties of water systems, thereby deteriorating ground stability. The economically developed soft clay areas face considerable threats from these acid environmental attacks. This study focused on employing a ''one-part'' geopolymer (OPG) comprising ground granulated blast furnace slag (GGBFS), fly ash (FA), and solid sodium hydroxide (NH) to stabilize the soft clay. Simultaneously, the deterioration behavior of OPG stabilized soft clay under two different acids (HNO3 and H2SO4) with various pH values (pH of 2, 4, and 6) and varied immersion periods up to 240 days was evaluated including the mass loss, neutralization depth (ND), pH value, and unconfined compressive strength (UCS). Additionally, scanning electron microscopy (SEM) and X-ray energy spectrometry (EDS) characterized the evolution of microstructure and hydrate composition of OPG-stabilized soft clay post varied acid immersion. The results highlighted the superior acid resistance of the stabilized soft clay with an 80:20 GGBFS/FA ratio compared to other ratios. The presence of significant hydration products, such as calcium silicate hydrates (C–S–H), calcium aluminate (aluminosilicate) hydrates (C-A-(S)–H), and sodium aluminosilicate hydrates (N-A-S-H), was observed in the OPG stabilized soft clay. In addition, the contents of Si in the OPG played a significant role in enhancing the acid resistance of the OPG stabilized soft clay. Based on these experimental results, two proposed mechanisms detailed the deterioration and acid resistance of the OPG stabilized soft clay under HNO3 and H2SO4 attack. The findings of this study contribute to advancing scientific comprehension concerning the acid resistance of the OPG stabilized soft clay in ground improvement practices.

Naringenin restricts the colonization and growth of Ralstonia solanacearum in tobacco mutant KCB-1.

Bacterial wilt severely jeopardizes plant growth and causes enormous economic loss in the production of many crops, including tobacco (Nicotiana tabacum). Here, we first demonstrated that the roots of bacterial wilt-resistant tobacco mutant KCB-1 can limit the growth and reproduction of Ralstonia solanacearum. Secondly, we demonstrated that KCB-1 specifically induced an upregulation of naringenin content in root metabolites and root secretions. Further experiments showed that naringenin can disrupt the structure of R. solanacearum, inhibit the growth and reproduction of R. solanacearum, and exert a controlling effect on bacterial wilt. Exogenous naringenin application activated the resistance response in tobacco by inducing the burst of reactive oxygen species and salicylic acid deposition, leading to transcriptional reprogramming in tobacco roots. Additionally, both external application of naringenin in CB-1 and overexpression of the Nicotiana tabacum chalcone isomerase (NtCHI) gene, which regulates naringenin biosynthesis, in CB-1 resulted in a higher complexity of their inter-root bacterial communities than in untreated CB-1. Further analysis showed that naringenin could be used as a marker for resistant tobacco. The present study provides a reference for analyzing the resistance mechanism of bacterial wilt-resistant tobacco and controlling tobacco bacterial wilt.

Enhancing permeability and mechanical properties of rubber cement-based materials through surface modification of waste tire rubber powder

In this study, the authors present a detailed investigation into the surface mineralization of recycled rubber powder (RP) to enhance its performance in cement mortars. A modified rubber, referred to as RTC, is produced by employing a straightforward and efficient method involving the deposition of tannic acid (TA) and calcium carbonate (CaCO3, <5 μm) on the surface of RP. The main objective of this research is to elucidate the impact of RTC on the impermeability, mechanical properties, and pore structure of rubberized mortar. Through a comprehensive set of characterizations and tests, we demonstrate the successful deposition of TA and CaCO3 on the RP surface, resulting in RTC with excellent chemical activity and hydrophilicity, while also providing nucleation sites for hydration products. This modification process facilitated improved interfacial affinity with cement paste, enhancing bonding between rubber and cement paste. Remarkably, the incorporation of rubber into mortars with markedly enhanced resistance to permeation, with RTC mortars demonstrating particularly noticeable improvement. The marginal decrease in density in comparison to conventional mortars arises from the rubber's lightweight properties. Moreover, rubber exerts a minor adverse influence on hydration kinetics, yet this detrimental impact is alleviated in mortars incorporating RTC. Notably, the study elucidates the nuanced changes in porosity induced by rubber incorporation, underscoring its influence on the mechanical performance of rubberized cement mortars. The RTC5 mortar with a 5% content demonstrates the most remarkable enhancement compared to RP5 mortar. Overall, this study highlights the potential of surface mineralization of RP as a promising approach for improving the performance of rubberized cement mortars.

Browning from headwaters to coastal areas in the boreal region: Trends and drivers

Browning of freshwaters, mainly caused by increased terrestrial organic carbon loading, has been widely studied during the last decades. However, there are still uncertainties regarding both the extent of browning in different aquatic ecosystems and the actual importance of different driving forces and mechanisms. To refine understanding of the extent and causes of browning and its temporal variation, we gathered a comprehensive dataset including 746 Finnish water quality monitoring stations representing various waterbody types: streams, rivers, lakes, and coastal waters. Monotonic trend analyses revealed that TOC concentrations increased in all waterbody types during the study period from 1990 to 2020, whereas non-linear trends indicated that upward trends in TOC concentrations have substantially decreased since the mid-2000s. However, despite the upward trends levelling off, non-linear analyses also indicated decreases in TOC concentrations at only a few stations. As a result, the TOC contents of the majority of Finnish waterbody types in 2020 were at a higher level than in 1990. To examine the driving forces of increasing TOC concentrations, we selected 100 riverine catchments and linked the detected trends to 24 different drivers, including both hydrometeorological and catchment characteristics. The increased TOC concentrations in surface waters could be connected to diverse human impacts: hydrometeorological variables impacted by climate change, decreased acidic deposition, and land use in terms of peatland drainage. The importance of increased temperatures was emphasized, and its role as a driver of increased leaching of organic carbon in the forthcoming years is expected to grow with climate change.

Critical loads for alkalization in terrestrial ecosystems

Critical loads are a risk assessment approach that has supported large decreases in atmospheric acidic deposition globally. In Canada, SOx emissions fell by approximately 70 % between 1990 and 2021, whereas total particulate matter (TPM) emissions increased by about 40 %, mostly after 2010. Base cations are a major component of TPM, and critical load models consider base cation deposition as beneficial to ecosystems insomuch as it reduces the risk of acidification. However, close to point sources, high levels of alkaline dust deposition have altered soil chemistry and caused an undesirable shift in ecosystem state; something that critical loads are designed to prevent. In this study, the simple mass balance model (SMB) was modified with the objective of preventing base cation accumulation in soil above an acceptable threshold. The concept was applied to a forested site close to large emission sources of sulphur, nitrogen, and base cations in the Oil Sands region of Alberta, Canada. At this site, base cation leaching measured at 25 cm was approximately three times higher than estimated background leaching and exceeded combined SO4 + NO3 leaching. The critical load for alkalization was exceeded under each scenario considered in this study, although the exceedance was marginal if all N in current deposition was assumed to leach from soil. While this framework can easily be applied to regional and national critical load efforts, the main uncertainties of the proposed approach include base cation deposition estimates, assumptions regarding the behavior of N in soil, the selection of an appropriate Alkle(crit) and the long-term immobilization of deposited base cations in soil.

Effects of Past Sulfur Deposition on the Soil Microbial Biomass at Spruce Forest Sites

During the last decades, forest soils in Central Europe recovered from former sulfur and acid deposition. As external S input into forests has strongly decreased and legacy S pools in the soils are diminishing, internal S cycling through mineralization will increasingly become important for ecosystem nutrition. However, it is not known how microbial biomass is affected by the S pool change in the formerly S surplus soils. Here, we present data on the status quo of C, N, and S in microbial biomass in relation to contents in mineral soil and organic layer. The results of forest soil in Eastern Germany (low and high liming), which is slowly recovering from former pollution, are compared to those of a site remote from air pollution in the Swiss Alps. The contents of C, N, and S in soil as well as in microbial biomass were clearly higher in the organic layer than in mineral topsoil at all sites. Despite the generally low content in the mineral A-horizon, the clean-air site showed indications of a more active S-turnover as compared to the high-pollution site. Liming at the high-pollution site improved the conditions for microbial growth (pH increase) in the organic layer resulting in more mobile S.

Long‐term changes in stream water chemistry in small forested watersheds in the northern Kanto region

AbstractConcerns have been raised regarding the degradation of stream water quality due to the excessive influx of atmospheric deposition. This study aimed to reveal the long‐term variation in stream water chemistry in approximately 40 forested small watersheds in the northern Kanto region, based on 3 surveys conducted in 1991–1992, 2006–2007, and 2022. The factors influencing each dissolved element were investigated. Regarding long‐term variations in stream water chemistry, relatively stable concentrations of cations (Ca2+, Mg2+, K+, and Na+) and SiO2 were observed. However, the concentrations of anions (Cl−, , and ) decreased due to the improvement in the atmospheric environment and the diminishing effect of fertilization. Furthermore, the recent increase in stream water pH was attributed to an increase in bicarbonate (), compensating for the decrease in anion concentrations relative to cations. Geology was the most significant factor for inter‐watershed variations in cations and SiO2, and this influence remained relatively constant over 30 years. Forest practices, especially fertilization, had a significant effect on Cl− and , and contributed to higher concentrations in the fertilized watersheds than in the non‐fertilized watersheds over the 15 years following fertilization. Sulfate deposition was a significant influencing factor for , and the concentration fluctuated under long‐term variations in deposition over the past 30 years. Despite substantial acid deposition in the study area, the absence of stream water acidification could be attributed to the abundant cation supply from bedrock and volcanic ash, which underwent weathering processes.

Macronutrients, metals, and metalloid concentrations in non-industrial wood ash in relation to provincial land application limits in Ontario, Canada

Non-industrial wood ash (NIWA) provided by residents who heat with wood, is rich in base-cations and other nutrients and may be used as a forest soil amendment to return nutrients lost through acid deposition. However, due to concerns regarding high trace metal concentrations, most wood ash is landfilled in Canada. This study investigated the chemical variability of NIWA of individual samples and homogenized mixtures to determine if they met Ontario provincial trace metal restriction limits. One hundred and seven ash and 10 charcoal samples collected from residents of Muskoka, Ontario, and three 10-sample composites were analyzed. Chemical composition varied among individual samples, but nutrient levels were within or higher than reported ranges for industrial wood ash, while trace metal values were lower. Ninety-seven percent (104 of 107) of the samples were within Ontario Regulation 267/03 of the Nutrient Management Act, and after homogenization, all samples were below soil application restriction limits. This study indicates that NIWA can be safely used as a forest soil amendment but recommends routine testing of batch samples prior to application.