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Biochar is widely used to improve soil physical properties and carbon sequestration. However, few studies focuse on the impact of maize stalk biochar on labile organic carbon (LOC) pool and the relationship between physical properties and LOC fractions. A field positioning experiment was performed in Mollisols region of Northeast China to evaluate the influence of maize stalk biochar on the spatial distribution and temporal changes of physical properties and LOC fractions. Maize stalk biochar treatments included C1 (1.5 kg ⋅ hm-2), C2 (3 kg ⋅ hm-2), C3 (15 kg ⋅ hm-2), C4 (30 kg ⋅ hm-2), and CK (0). The results showed that maize stalk biochar increased soil water contents (SWC) and soil porosity (SP), but reduced bulk density (BD). Maize stalk biochar reduced dissolved organic carbon (DOC) contents in the 0-20 cm soil layer, ranging from 0.25 g ⋅ kg-1 to 0.31 g ⋅ kg-1 in harvest period, while increased in the 20-40 cm soil layer. In addition, the application of biochar had a significant impact on the spatial distribution and temporal change of SWC, BD, SP, DOC, hot-water extractable carbon (HWC), acid hydrolyzed organic carbon (AHC I, II), and readily oxidized organic carbon (ROC). High amounts of maize stalk biochar up-regulated the contents of soil organic carbon SOC, HWC, AHC I, AHC II, and ROC. In addition, SWC and SP were the key physical factors to affect LOC fractions. In conclusions, maize stalk biochar could improve physical properties, and then influence LOC fractions, and maize stalk biochar could be used as an organic amendment for restoring degraded soils governed by their rates of addition. [ABSTRACT FROM AUTHOR]

Effective filtration depends on a combination of complex physical and chemical mechanisms. It's important for operators to know how granular media filters work, the basics of how they are designed, and strategies for successful operation. [ABSTRACT FROM AUTHOR]

This paper addresses the regulation of water quality influencers such as Organic Nitrogen, Ammonia Nitrogen, Nitrate Nitrogen, Dissolved Organic Carbon and Dissolved Oxygen for a sub-surface flow horizontal wetland in a controlled environment. The plant uncertainty is quantified by using measurement data. The robust control of the process is achieved using a decentralized quantitative feedback theory based control strategy. The control structure also employs a feed-forward mechanism to minimize loop interactions and feedback control to ensure stability, tracking and disturbance rejection. The numerical simulations and hardware-in-loop implementation show that the performance specifications are robustly met. • The control of water quality deciding variables by using a constructed wetland • The parametric uncertainty is quantified using measurement data collected • A decentralized quantitative feedback theory based robust controller is adopted • Each loop is equipped with feed-forward controllers to minimize coupling effects • Performance is verified by numerical simulation and hardware-in-Loop validation [ABSTRACT FROM AUTHOR]

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

Soil dissolved organic carbon (DOC) is the most active part in forest soil carbon pool, the responses of which to climate warming has profound effects on forest carbon cycling. Based on a manipulative soil warming experiment in subtropical evergreen broad-leaved forests, we collected soil solutions in situ and used ultraviolet-visible, infrared and three-dimensional fluorescence spectroscopy analyses to explore the effects of soil warming (+4 °C, 1 year) on soil DOC quantity and quality along the soil profile. The results showed that soil DOC flux remained constant along the soil profile. Soil DOC mainly included two humic-like fractions and one microbial metabolite. Warming significantly decreased soil DOC flux and the abundance of aromatic and hydrophobic components, and increased the amount of low molecular weight carbohydrates. Furthermore, soil warming increased the relative proportion of humic-like fractions in the surface soil layer (0-10 cm) and microbial metabolite in the deep soil layer (30-40 cm), indicating that warming might accelerate microbial turnover in the deep layer. Overall, soil warming not only decreased soil DOC content' but also simplified the composition of soil DOC in subtropical evergreen broad-leaved forests. [ABSTRACT FROM AUTHOR]

The Ulva prolifera bloom is considered one of the most serious ecological disasters in the Yellow Sea in the past decade, forming a carbon sink in its source area within a short period but becoming a carbon source at its destination. To explore the effects of different environmental changes on seawater dissolved carbon pools faced by living U. prolifera in its originating area, U. prolifera were cultured in three sets with different light intensity (54, 108, and 162 μmol m−2 s−1), temperature (12, 20, and 28 °C) and nitrate concentration gradients (25, 50, and 100 μmol L−1). The results showed that moderate light (108 μmol m−2 s−1), temperature (20 °C), and continuous addition of exogenous nitrate significantly enhanced the absorption of dissolved inorganic carbon (DIC) in seawater by U. prolifera and most promoted its growth. Under the most suitable environment, the changes in the seawater carbonate system were mainly dominated by biological production and denitrification, with less influence from aerobic respiration. Facing different environmental changes, U. prolifera continuously changed its carbon fixation mode according to tissue δ13C results, with the changes in the concentrations of various components of DIC in seawater, especially the fluctuation of HCO 3 − and CO 2 concentrations. Enhanced light intensity of 108 μmol m−2 s−1 could shift the carbon fixation pathway of U. prolifera towards the C 4 pathway compared to temperature and nitrate stimulation. Environmental conditions at the origin determined the amount of dissolved carbon fixed by U. prolifera. Therefore, more attention should be paid to the changes in marine environmental conditions at the origin of U. prolifera , providing a basis for scientific management of U. prolifera. [Display omitted] • Moderate light, temperature and nitrate addition boost U. prolifera DIC absorption. • U. prolifera adapts carbon fixation modes to environmental changes. • Origin environmental conditions determine U. prolifera's carbon sink contribution. [ABSTRACT FROM AUTHOR]

Lake browning is considered a severe water quality problem in lake ecosystems, but it has received considerably less attention in water protection than eutrophication. Current metrics used in lake surveillance monitoring programmes, including the European Union's Water Framework Directive, do not reflect browning sufficiently. The aims of the study were to explore the potential role of the functionality of rotifers as browning indicators and to improve understanding of the environmental parameters driving the functionality and diversity of rotifers. Seasonal data on rotifer communities and water quality from seven lakes with differing water colour and trophic conditions were analysed. The feeding guilds of rotifers enabled differentiation between lakes in terms of their ecological conditions, and, in particular, eutrophic and brown-water lakes were clearly distinguished from other lakes. The guild ratio of rotifers was positively affected by water colour, but inversely related to total phosphorus concentration. Our results suggest that zooplankton functionality provides a potential tool to assess ecosystem dynamics, particularly when assessing lake browning. Thus, our results suggest that application of the guild ratio of rotifers is a promising method to estimate the general browning status of lakes and may complement the metrics used in Water Framework Directive. [Display omitted] • Bioindicators that respond to lake browning are needed. • The functionality of rotifers as a browning indicator was studied. • Predominant feeding mode expressed the ecological conditions of lakes. • Functionality of rotifers provide a potential tool to assess browning status of lakes. [ABSTRACT FROM AUTHOR]

Large nutrient levels and herbivory stress, particularly when acting together, drive a variety of responses in seagrass communities that ultimately may weaken their carbon balance. An in situ three-months experiment was carried out in two contrasting seasons to address the effects of two levels of nutrient load and three levels of artificial clipping on Cymodocea nodosa plants. Nutrient enrichment shifted the community from autotrophic to heterotrophic and reduced DOC fluxes in winter, whereas enhanced community carbon metabolism and DOC fluxes in summer. Herbivory stress decreased the net primary production in both seasons, whereas net DOC release increased in winter but decreased in summer. A reduction of seagrass food-web structure was observed under both disturbances evidencing impacts on the seagrass ecosystems services by altering the carbon transfer process and the loss of superficial OC, which may finally weaken the blue carbon storage capacity of these communities. • Effects of nutrients and simulated herbivory on seagrass C dynamics and biodiversity • An in situ 3-months experiment in two seasons in a full factorial design • Seagrass production–DOC fluxes relationship can be altered under disturbance conditions. • 90 % leaf clipping under nutrient increase stimulate respiration and loss of sediment OC • Fewer trophic groups and links connecting top to basal species under disturbances [ABSTRACT FROM AUTHOR]

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

This study examined the effects of solar light driven plastic degradation on carbon chemistry in the coastal waters of eastern Arabian Sea along the west coast of India. The research was conducted through experimental incubations exposed to natural sunlight at multiple locations between December 2023–February 2024. Photodegradation induced a significant pH decrease (up to 0.38 ± 0.02) between controls and plastic incubations ranging from 8.17 ± 0.01 to 7.54 ± 0.02 with the highest variation in the Mumbai coast ranging from 8.13 ± 0.01 to 7.75 ± 0.03. pH variations are primarily caused by the leaching of organic acids and CO 2 release during solar irradiated incubation. Plastic leaching due to natural light irradiation and subsequent changes in the water chemistry is of prime significance with dissolved organic carbon (DOC) leaching of 0.002–0.03% of plastic weight into the coastal waters. Our estimations suggest 15–75 metric tonnes (MT) of DOC release per year by plastic pollution in the eastern Arabian Sea coastal waters. Further, the fluorescent dissolved organic matter (FDOM) fragmentation, a part of DOC, may act as an organic source of synthetic contaminants and would promote heterotrophic microbial action in the coastal waters. Photodegradation of plastic and the interaction of natural DOC and plastic-derived DOC resulted in longer wavelengths FDOM, which may affect the penetration of photosynthetically active radiation in the water column, thereby impacting primary production. Finally, future research work focussing on the role of plastic pollution in coastal ocean acidification and vice-versa is essential and will be increasingly intense in the upcoming decades. [Display omitted] • Dissolved organic carbon leaching corresponds to 0.002–0.03% of aged plastics weight. • PH decreases as a consequence of plastic photodegradation. • Plastic pollution may release 15–75 MT DOC year−1 in the studied coastal waters. • Plastic-derived longer wavelengths FDOM becomes a source of secondary pollution. • Warming and ocean acidification may intensify the plastic photodegradation. [ABSTRACT FROM AUTHOR]

Straw returning is an important way to increase soil organic matter. Pot experiment under greenhouse conditions was conducted to investigate the phytoavailability and chemical speciation of cadmium(Cd) in two different types of Cd contaminated soil with crop straw incorporation. Results indicated that uptake of Cd by maize was increased by crop straw incorporated into both natural Cd-contaminated soil and artificial Cd-contaminated soil. Crop straw incorporation also increased soil pH and dissolved organic carbon(DOC). Meanwhile the water soluble Cd concentration was increased in natural Cd-contaminated soil but decreased in artificial Cdcontaminated soil when the soil DOC increased. Majority of Cd existed in exchangeable fraction, but the concentration of Cd in exchangeable fraction reduced significantly with crop straw incorporated into both the two types of Cd-contaminated soil. Carbonate Cd concentration was increased in artificial Cd-contaminated soil. Therefore, crop straw incorporation may be a workable way to remediate soil, but the potential risk should be evaluated. [ABSTRACT FROM AUTHOR]

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

Absence of dissolved oxygen (anoxia) in the hypolimnion of lakes can eliminate habitat for sensitive species and may induce the release of sediment‐bound phosphorus. Lake anoxia generally results from decomposition of organic matter, which is exacerbated by high nutrient loads. Total phosphorus (TP) in lakes is regulated by static aspects of the lake's watershed, but lake TP can be readily increased by human activities. In some low‐nutrient lakes, basin morphometry may induce naturally occurring anoxia. The occurrence of natural anoxia is especially important to consider in lake water quality assessments that compare observed conditions to expected reference conditions. To investigate the occurrence of natural vs. anthropogenically influenced anoxia, we constructed a logistic regression model to calculate the probability of low‐nutrient lakes (TP < 15 µg/L) developing aerial anoxic extent ≥10% by testing the predictive potential of variables related to basin morphometry, depths of lake thermal strata, epilimnetic TP, and dissolved organic carbon (DOC). Maximum lake depth and the proportion of lake area under the top of the metalimnion were the most important variables to predict the likelihood of hypolimnetic anoxia, which correctly predicted anoxic condition in 84% of lakes (Model 1). Adding TP as a third variable to Model 1 produced a significantly improved model (Model 2) but the prediction success rate was comparable (86%). We also present a model for lakes with limited bathymetric data, which predicts anoxia with 81% accuracy based on maximum lake depth and mean thermocline depth at peak stratification. DOC was relatively low (4.3 ± 1.5 mg/L [mean ± SD]) in the study lakes and its inclusion did not improve model performance. In Model 1, lakes with an anoxic extent ≥10% of lake area had significantly higher epilimnetic TP than lakes with oxic hypolimnia, regardless of prediction category or success. Our results indicate that including TP as a variable helps refine models based on morphometry alone, but lake morphometry and stratification dynamics are the most important factors in the development of anoxic extent in low‐nutrient temperate lakes. Our approach informs studies concerned with identifying key factors that influence regime shifts in a variety of ecosystems. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) is a global environmental concern, and submarine groundwater discharge (SGD) is a potentially process that enhances OA. This review summarizes the relationship between two types of constituents carried by SGD into China's seawater and OA. 1) Current research predominantly concentrates on constituent fluxes from SGD, neglecting its ecological impacts on carbon and nutrients budgets, as well as the mechanisms between carbon and nutrients. 2) Uncertainties persist in SGD research methods and acidification characterization. 3) There's a need to enhance quantitative research methods of SGD-OA, particularly in areas with intricate biogeochemical processes. Effective identification methods are crucial to quantify SGD's contribution to OA. Investigating core scientific questions, including SGD's impact on OA rates and scales, is paramount. While the primary focus is on SGD-OA research in China, insights gained from novel perspectives could have broader value for coastal management globally. [Display omitted] • Uncertainties exist in SGD and coastal acidification characterization. • Relative paucity of studies on SGD input carbon at different scales in China. • Consider coupling of SGD-carried nutrients and carbon to coastal acidification. • Consider conducting qualitative and quantitative studies on SGD and acidification. [ABSTRACT FROM AUTHOR]

Heterogeneous catalytic ozonation has received increasing popularity in wastewater treatment across China. However, some challenges, such as metal leaching from catalysts, still exist. Meanwhile, it is lesser known about its removal efficiency of dissolved organic carbon and impact on biological toxicity in pilot-scale applications. Here we synthesized an Al-based catalyst (Mn-Fe/Al 2 O 3) for catalytic ozonation in pilot-scale. Results of characterization show that Mn and Fe were effectively supported on porous alumina and formed chemical bonds. The catalytic ozonation process could generate hydroxyl radical, superoxide radical and singlet oxygen for the deep degradation of dissolved organic carbon. Its chemical oxygen demand removal efficiency (average removal of 14.5 mg/L) could meet the requirement of Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant (GB 18918-2002) in China with acceptable metal leaching. The process also effectively removed dissolved organic carbon, especially the hydrophobic fractions (99 % removal). In toxicogenomics assay, the total transcriptional effect level index value for the effluent (1.40) was ≤ 1.50, indicating there was no obvious toxic effect for ecosystem. Based on economical estimation, the operational cost of the catalytic ozonation was 0.09 $/m3, much less than previous reported cases. This study provides convincing evidence for the effectiveness of Mn-Fe/Al 2 O 3 catalytic ozonation in future wastewater treatment. [Display omitted] • An Al-based catalyst was synthesized for catalytic ozonation in pilot-scale. • Mn-Fe/Al 2 O 3 could generate reactive oxygen species to degrade organics. • Mn and Fe forming chemical bonds with porous alumina reduced metal leaching. • Toxicogenomics assay showed no obvious toxic effect via catalytic ozonation. • Operational cost of catalytic ozonation was less than previous reported cases. [ABSTRACT FROM AUTHOR]

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

Studies of recovery from acidic deposition have focused on reversal of acidification and its associated effects, but as recovery proceeds slowly, chemical dilution of surface waters is emerging as a key factor in the recovery process that has significant chemical and biological implications. This investigation uses long-term chemical records from 130 streams in the Adirondack region of New York, USA, to evaluate the role of ongoing decreases in conductance, an index of dilution, in the recovery of these streams. Stream chemistry data spanning up to 40 years (1980s–2022) showed that acid-neutralizing capacity has increased in 92% of randomly selected streams, but that harmful levels of acidification still occur in 37% of these streams. Conductance and Ca2+ concentrations decreased in 79% of streams, and SO 4 2− concentrations in streams continued to show strong decreases but remained several times higher than concentrations in precipitation. These changes were ongoing through 2022 even though acidic deposition levels were approaching those estimated for pre-industrialization. Further dilution is continuing through ongoing decreases in stream SO 4 2−. Nevertheless, Ca2+ continued to be leached from soils by SO 4 2−, organic acids and NO 3 −, limiting the replenishment of available soil Ca2+, a prerequisite to stem further dilution of stream water. As recovery from acidic deposition proceeds slowly, chemical dilution of surface waters emerges as a key factor in the recovery process.Chemical records from 130 streams in the Adirondack region of New York show widespread decreases in conductance that are ongoing even as acidic deposition levels approach those estimated for the early 1900s.Further dilution is likely as release of SO 4 2− from soils at a gradually decreasing rate continues into the future. [Display omitted] • Chemical recovery from acidic deposition in Adirondack streams is widespread but incomplete. • Recovery remains slow despite atmospheric deposition nearing pre-industrial levels. • Dilution of stream chemistry is emerging as a key factor in recovery. • Accumulated effects of acidic deposition on soils are now driving dilution. • Dilution is slowing recovery by increasing dissolved organic carbon mobilization. [ABSTRACT FROM AUTHOR]

Seawater samples were collected from April 6 to September 6, 2017 in the Southern Yellow Sea, China where green tides often occurred, and analyzed for nutrients, dissolved organic carbon (DOC), and fluorescent dissolved organic matter (FDOM). The DOC concentrations increased significantly in the green tide areas by approximately 1.2 times compared to those in the non-green tide areas. From the large-scale outbreak to the complete dissipation of the green tide, the fluorescence intensities of the four FDOM fluorescent components identified in the green tide areas were significantly higher than those in the non-green tide areas. During the extinction period, the fluorescence intensities of the three humus-like components and one protein-like component were approximately 1.8 and 1.3 times higher than those in the non-green tide areas, respectively. These findings suggested that the outbreak of green tide could release DOM into water and affect the biogeochemical cycle in green tide regions. • DOC increased 20% in the green tide areas during the outbreak of Ulva prolifera. • The fluorescent components were significantly higher in the green tide areas. • DON in the green tide areas increased 30% than those in the non-green tide areas. • When Ulva decayed, it released FDOM and DON into the water. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) is not only a critical component of global and regional carbon budgets, but also an important precursor for carcinogenic disinfection byproducts (DBP) generated during drinking water disinfection process. The lack of process based watershed scale model for carbon cycling has been a limiting factor impeding effective watershed management to control DOC fluxes to source waters. Here, we integrated terrestrial and aquatic carbon processes into the widely tested Soil and Water Assessment Tool (SWAT) watershed model to enable watershed-scale DOC modeling (referred to as SWAT-DOC hereafter). The modifications to SWAT mainly fall into two groups: (1) DOC production in soils and its transport to aquatic environment by different hydrologic processes, and (2) riverine transformation of DOC and their interactions with particular organic carbon (POC), inorganic carbon and algae (floating and bottom). We tested the new SWAT-DOC model in the Cannonsville watershed, which is part of the New York City (NYC) water supply system, using long-term DOC load data (from 1998 to 2012) derived from 1399 DOC samplings. The calibration and verification results indicate that SWAT-DOC achieved satisfactory performance for both streamflow and DOC at daily and monthly temporal scales. The parameter sensitivity analysis indicates that DOC loads in the Cannonsville watershed are controlled by the DOC production in soils and its transport in both terrestrial and aquatic environments. Further model uncertainty analysis indicates high uncertainties associated with peak DOC loads, which are attributed to underestimation of high streamflows. Therefore, future efforts to enhance SWAT-DOC to better represent runoff generation processes hold promise to further improve DOC load simulation. Overall, the wide use of SWAT and the satisfactory performance of SWAT-DOC make it a useful tool for DOC modeling and mitigation at the watershed scale. • We describe a watershed scale DOC model integrating terrestrial and aquatic processes. • SWAT-DOC reproduces well long-term streamflow and DOC fluxes at different time scales. • Modeling analyses indicate DOC fluxes simulations are limited by transportation during high flow events. • SWAT-DOC holds promise to support assessment of DOC related disinfection byproducts risks. [ABSTRACT FROM AUTHOR]

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

Abstract Ailian Bay is an integrated multi-trophic aquaculture bay with approximately 60 years maricultural activities in North China. The floating raft culture of kelp and shellfish is the unique mariculture mode. In this study, the impacts of intensive mariculture activities on seasonal carbon and nutrient dynamics in Ailian Bay were systematically analysed via seasonal surveys between 2015 and 2016. The dissolved inorganic nitrogen and silicon reached the maximum concentrations during summer, which were mainly attributed to the release of shellfish metabolic by-products and their filter-feeding effects on diatoms. Dissolved organic carbon (DOC) concentrations were significantly elevated when kelps were rotting in summer and kelp seeding were occurring in winter. Meanwhile, the fluorescence intensity of humic-like chromophoric dissolved organic matter was relatively high in kelp mariculture zone. As most humic-like DOC are potentially refractory substances, we propose that kelp mariculture would contribute importantly to the increase of refractory DOC pool in oceans. Highlights • Ailian Bay is an IMTA bay with long-term raft-culture activities in North China. • Seasonal dynamics of DOC and nutrients are clearly impacted by mariculture. • Kelp mariculture produces high concentrations of DOC in Ailian Bay. • Partial DOC produced from kelp mariculture is potentially recalcitrant. • The DOC varies greatly during different periods of shellfish mariculture. [ABSTRACT FROM AUTHOR]

• The DOC released from plastic that can be used by microorganisms in soil. • Plastic carbon participated in soil carbon cycle was confirmed. • PE plastic farmland in northwest China, 1.39 × 105 tons of excess CO 2 emissions. • Replace PE plastic film with biodegradable film, 7.5-fold more excess CO 2 emissions. Plastic film mulching is an important agricultural practice, but its accumulation in soil threatens soil health. Here, we explored the effects of plastic film on soil carbon cycling through microcosmic incubation and estimated the excess carbon dioxide (CO 2) emissions of farmland soils through Meta-analysis. The results showed that plastic film released dissolved organic carbon (DOC) into the soil, which was rapidly used by microorganisms and accelerated the decomposition of soil organic carbon (SOC), increasing CO 2 emissions. Soil moisture content and soil carbon content affected the rate of DOC release from plastic. We estimated that residual plastic film farmland in six northwest provinces of China, 1.39 × 105 tons of excess CO 2 emissions in 2020. The soil excess CO 2 emissions was influenced by polyethylene (PE) plastic concentration and soil type. Replace PE plastic film with biodegradable film, 1.05 × 106 tons of excess CO 2 emissions, 7.5 times that of PE plastics. [Display omitted] [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) is a powerful regulator of the ecotoxicity of ciprofloxacin (CIP), a widely applied fluoroquinolone antibiotic. In this study, we investigated the impact of DOC from a variety of sources on CIP bioavailability, using a cyanobacteria growth inhibition test with Microcystis aeruginosa. We analyzed the impact from two perspectives: (1) DOC concentration, and (2) water brownness, defined in this work as the light absorbance of DOC solutions. The toxicity tests were conducted with (1) unprocessed freshwater DOC in the naturally occurring state, (2) DOC extracted from a freshwater stream (Schwarzbach stream, Küchelscheid, Belgium), and (3) the commercial DOC product Suwannee River organic matter. Across all DOC sources investigated, a strong negative correlation was observed between CIP ecotoxicity and light absorbance at four wavelengths across the ultraviolet–visible range (e.g., A 350), whereas CIP ecotoxicity correlated poorly with the DOC concentration. In addition, the interactions between CIP and DOC were modelled as a CIP-DOC binding process to allow the quantification of the inhibitory effects of DOC on CIP toxicity via binding constants (K d,CIP x, with x being the ionic charge + or +/−, L g−1). Processed DOC sources showed higher binding potency than most of the unprocessed DOC sources, suggesting that toxicity tests employing only processed DOC potentially overestimates the impact of DOC in natural environments. Nonetheless, the light absorption coefficient (i.e., ε 350) appeared a reliable predictor of the K d,CIP +/− (and thus of the potential of the DOC source to reduce ecotoxicity of CIP) of both processed and unprocessed DOC. The relationship can be further incorporated into model simulations to estimate CIP bioavailability in dynamic environments. It is concluded that the brownness of water is a better predictor of the impact of DOC on CIP bioavailability than the DOC concentration itself. [Display omitted] • Dissolved organic carbon (DOC) inhibits the ecotoxicity of ciprofloxacin. • DOC concentration is a poor indicator of ciprofloxacin bioavailability. • The DOC inhibitory effect can be predicted by light absorption properties. [ABSTRACT FROM AUTHOR]

Biochar is considered a promising material for carbon sequestration owing to its high stability. However, the effects of biochar properties, especially pore structure and persistent free radical (PFR) content, on its microbial resistance stability (MRS) remain unclear. Incubation experiments were conducted to investigate the anaerobic and aerobic MRS of rice straw biochar produced at 300–700 °C, with and without vermiculite modification, and to evaluate the relationship between key biochar properties and MRS. The results showed that PFR signal intensity in biochar was much higher under anaerobic conditions than that under aerobic conditions, increasing with production temperatures of 300–600 °C, but sharply decreasing at 700 °C. Anaerobic MRS of biochar produced at 700 °C was lower than that of biochar produced at 300–600 °C, as indicated by higher CH 4 emission. Redundancy analysis revealed a negative correlation between PFR concentration and cumulative CH 4 emission with a correlation coefficient of –0.467, and a positive correlation between cumulative CH 4 emission and pore volume and specific surface area with correlation coefficients of 0.405 and 0.281, respectively. Biochar dissolved organic carbon content and pH were the two most important factors affecting aerobic MRS as reflected by their high correlation coefficients (0.933 and –0.848) with cumulative CO 2 emission. Vermiculite modification enhanced MRS and accordingly lowered the global warming potential of biochar produced at low temperature (300–500 °C) by 4.59–20.2 % and 15.3–42.9 % under anaerobic and aerobic conditions, respectively. However, it had a contrasting effect on biochar produced at 700 °C. Biochar would be more effective at mitigating global warming in paddy fields than in dry lands. [Display omitted] • Persistent free radicals (PFRs) are abundant in rice straw biochar. • PFRs affected biochar anaerobic MRS due to negative effects on CH 4 emissions. • Dissolved organic carbon and pH were crucial factors affecting biochar aerobic MRS. • Vermiculite enhanced both anaerobic and aerobic MRS of lower-temperature biochar. • Higher-temperature biochar showed greater global warming mitigation potential. [ABSTRACT FROM AUTHOR]

Nickel (Ni) emissions resulting from production and transportation raise concerns about the impact of Ni exposure to marine ecosystems. Ni bioavailability models are established for FW systems, but the influence of chemical parameters (e.g. dissolved organic carbon (DOC)) on Ni toxicity within marine systems is less well understood. To examine the effects of DOC concentration and composition on Ni toxicity, acute toxicity tests were conducted on early life-stages of blue mussels ( Mytilus edulis ) and sea urchin embryos ( Strongylocentrotus purpuratus ) in full strength sea water (32 ppt). Nine different field collected samples of water with varying concentration (up to 4.5 mg C/L) and composition of DOC were collected from the east coast of the United States. Organic matter compositional analysis included molecular fluorescence and absorbance spectroscopy. The different DOC sources had different protective effects against embryo toxicity. The control (no DOC) Ni 48 h-EC 50 for Mytilus embryos was 133 µg/L (95% confidence interval (C.I.) of 123–144 µg/L), while Strongylocentrotus embryos displayed control 96-h EC 50 values of 207 µg/L (167–247 µg/L). The most significantly protective sample had high humic acid concentrations (as determined from fluorescence spectroscopy), which yielded an EC 50 of 195 µg/L (169–222 µg/L) for Mytilus , and an EC 50 of 394 µg/L (369–419 µg/L) for S. purpuratus . Among all samples, protection was related to both DOC quantity and quality, with fluorescence-resolved humic and fulvic acid concentrations showing the strongest correlations with protection for both species. These data suggest that DOC is protective against Ni toxicity in M. edulis and S. purpuratus , and that accounting for a DOC quality factor will improve predictive toxicity models such as the biotic ligand model. [ABSTRACT FROM AUTHOR]

Because the freely dissolved fraction of highly hydrophobic organic chemicals is bioavailable, knowing the partition coefficient between dissolved organic carbon and water ( K DOCw ) is crucial to estimate the freely dissolved fraction from the total concentration. A kinetic method was developed to obtain K DOCw that required a shorter experimental time than equilibrium methods. The equilibrium partition coefficients of four polychlorinated biphenyls (PCBs) (2,4,4′-trichlorobiphenyl (PCB 28), 2,2′,3,5′-tetrachlorobiphenyl (PCB 44), 2,2′,4,5,5′-pentachlorobiphenyl (PCB 101), and 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153)) between dissolved organic carbon and seawater ( K DOCsw ) were determined using seawater samples from the Korean coast. The log K DOCsw values of PCB 28 were measured by equilibrating PCB 28, the least hydrophobic congener, with seawater samples, and the values ranged from 6.60 to 7.20. For the more hydrophobic PCBs (PCB 44, PCB 101, and PCB 153), kinetic experiments were conducted to determine the sorption rate constants ( k 2 ) and their log K DOCsw values were obtained by comparing their k 2 with that of PCB 28. The calculated log K DOCsw values were 6.57–7.35 for PCB 44, 6.23–7.44 for PCB 101, and 6.35–7.73 for PCB 153. The validity of the proposed method was further confirmed using three less hydrophobic polycyclic aromatic hydrocarbons. This kinetic method shortened the experimental time to obtain the K DOCsw values of the more hydrophobic PCBs, which did not reach phase equilibrium. [ABSTRACT FROM AUTHOR]

Bioavailable dissolved organic carbon (B DOC ), nitrogen (B DON ) and their degradation rate constants were measured for the Chilika Lagoon, India. Long-term laboratory incubation experiments (90 days) were conducted at a constant temperature (25 °C) to quantify the bioavailable dissolved organic matter (DOM) and the possible degradation rate coefficients. The results showed that 41 ± 12% of dissolved organic carbon (DOC) and 47 ± 17% of dissolved organic nitrogen (DON) were B DOC and B DON respectively, with their stoichiometry found to be higher than the Redfield ratio. A first order exponential non-linear fitting routine was used to estimate pool sizes. The degradation rate constant (k) for the B DOC varied from 0.127–0.329 d −1 and B DON from 0.043–0.306 d −1 during the study period. Half-lives of the B DOC and B DON ranged from 2.1–5.4 and 2.2–15.9 days, respectively. Overall, the results showed that a fraction of the labile DON was transported from the lagoon to the adjacent coastal sea. [ABSTRACT FROM AUTHOR]

Land-use change can modify terrestrial ecosystem processes with potentially important effects on below-ground carbon dynamics. Soil microbes are considered the rate-limiting factor in carbon decomposition. However, the effect of land-use change on soil microbial community and the mechanism of soil carbon dynamics remain unclear. In this study, soil samples were collected during four periods (April, June, August, and October) at sites in the Loess Plateau in China with different land- use types: Robinia pseudoacacia L. (RP) and abandoned land (AL); these areas were converted 40 years ago from similar farmlands, while the millet ( Setaria italica ) farmlands (FL) were selected as a control in our study. Quantitative PCR and Illumina sequencing of the 16S rRNA and ITS genes were performed to analyze the abundance, diversity, and compositions of the soil microbes (bacteria and fungi). Additionally, soil organic carbon fractions (soil organic carbon: SOC, dissolved organic carbon: DOC, microbial biomass carbon: MBC) and soil respiration components (soil respiration: SR, heterotrophic respiration: HR, autotrophic respiration: AR) were evaluated. The results showed that SOC fractions and soil respiration increased after land-use change, with significant correlation being observed. In particular, DOC was more related to SR and HR than to the other fractions. Moreover, the abundance and diversity of the microbes (bacteria and fungi) were greatly affected by the land- use change; both of them were significantly and positively correlated with soil organic carbon fractions and soil respiration components. For dominant bacterial phyla, both Proteobacteria and Bacteroidetes were significantly more abundant in the afforested soil than in the FL, while the abundances of Actinobacteria and Chloroflexi ranked as FL > AL > RP. For dominant fungal phyla, Ascomycota responded positively to land- use changes, whereas Basidiomycota responded negatively. Such changes in the abundances of microbial phyla were significantly correlated with the linkage of soil organic carbon fractions and respiration components. Altogether, these results suggest that the changes in components of soil respiration may be highly susceptible to soil organic carbon fractions, especially to DOC, and this linkage is largely modulated by microbial community across land-use changes. [ABSTRACT FROM AUTHOR]

Copyright of Brazilian Journal of Oceanography is the property of Instituto Oceanografico da Universidade de Sao Paulo and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Lowland streams are often revitalized by hydrologically reconnecting their surrounding terrestrial environment, which likely alters central ecosystem functions such as autotrophic and heterotrophic carbon and nutrient metabolism. However, such central ecosystem functions of stream reaches following revitalization have rarely been investigated. Here, we measured net-uptake of nitrate and of various dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) fractions (using size-exclusion chromatography, SEC), as well as fluorescence components (established by parallel factor analysis, PARAFAC) repeatedly along a revitalized 1.4 km reach of a Danish lowland stream during base flow conditions. Samples were taken at six stations every three hours for one day. We measured discharge at five of the six stations to calculate whole-stream net-uptake. Moreover, we continuously measured oxygen at the start and at the end of the reach to assess stream metabolism, and took piezometer samples from ten shallow groundwater sites to assess potential determinants of organic matter and nitrate metabolism. We found high metabolic activity within the stream reach with a gross-primary production of 4.8 and 3.6 g O 2 m −2 day −1 and a production to respiration ratio of 0.8 and 0.9 at the start and end of the reach, respectively. Nitrate exhibited relatively constant high net-uptake rates of 0.41–0.52 g N m −2 d −1 , which varied little and were not related to the time of the day. Therefore, autotrophic nitrate uptake for was likely of minor importance, despite the apparently high primary production. In contrast, SEC DON and DOC fractions, as well as PARAFAC components did not suggest net-uptake or release. Instead, DOC and DON concentration were highly variable among the six stations and sampling times, a pattern that was not explainable by measurement errors but was likely related to the high variability of DOC and DON concentrations in the hyporheic zone and adjacent groundwater bodies. This pointed to a potentially high interaction with the hyporheic and riparian zone, underlining the strong linkage of DOM-related processes across the terrestrial-aquatic boundary. The high nitrate uptake points to the high retention potential of revitalized stream reaches, which, however, would need to be corroborated by further studies with reference reaches. [ABSTRACT FROM AUTHOR]

Release and microbial degradation of dissolved organic matter (DOM) and chromophoric dissolved organic matter (CDOM) from the macroalgae Ulva prolifera were studied in laboratory incubation experiments. The release of DOM and CDOM from Ulva prolifera was a rapid process, and hydrolysis played an important role in the initial leaching of the organic compounds from the algae. Bacterial activity enhanced the release of DOM and CDOM during degradation of the algae and utilization of the released organic compounds. It is calculated that 43 ± 2% of the C and 63 ± 3% of the N from Ulva prolifera 's biomass were released during the 20-day incubation, and 65 ± 3% of the released C and 87 ± 4% of the released N were utilized by bacteria. In comparison, only 18 ± 1% of the algae's C and 17 ± 1% of its N were released when bacterial activities were inhibited. The fluorescence characteristics of the CDOM indicate that protein-like DOM was the major organic component released from Ulva prolifera that was highly labile and biodegradable. Bacteria played an important role in regulating the chemical composition and fluorescence characteristics of the DOM. Our study suggests that the release of DOM from Ulva prolifera provides not only major sources of organic C and N, but also important food sources to microbial communities in coastal waters. [ABSTRACT FROM AUTHOR]

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

Field measurements of dissolved organic carbon (DOC) concentration and remote-sensing reflectance were conducted to develop a regional, empirical red-blue algorithm to retrieve surface DOC from Geostationary Ocean Color Imager (GOCI) data for Lake Taihu, China. The auxiliary data (in-situ observations of the optical properties and water quality, buoy measurements of hydrodynamic data and water chemical parameters) were used to investigate the spatial and temporal variations in DOC. GOCI was shown to be capable of successfully obtaining hourly variations in DOC, with a root mean square error percentage (RMSP) of 17.29% (RMSE = 0.69 mg/L) for the match-up data. The GOCI-derived DOC in Lake Taihu confirms that the highest DOC concentration is in northwest Lake Taihu, followed by Meiliang Bay, Gonghu Bay and northeast Lake Taihu. Hourly DOC variation is significant and presents a different trend for each lake segment due to the variety of influencing factors. Discharge of DOC from surrounding rivers is an important factor to the variation of DOC in northeast Lake Taihu. However, organic products of algae will be the primary contributor to DOC when algal bloom occurred. During the period of algal bloom, high DOC levels in Lake Taihu can lead to hypoxia when coupled with high temperatures and low disturbance. [ABSTRACT FROM AUTHOR]

The possible impact of three types of anthropogenic surfactants on the ability of marine dissolved organic carbon (DOC) to form self-assembled microgels was evaluated. The behavior of existing native microgels was also examined in the presence of surfactants. These results reveal that the release of surfactants even at low concentrations into the aquatic environment could effectively hinder the self-assembly of DOC polymers. The extent of the size reduction had the following order: anionic, cationic, and non-ionic. Furthermore, charged surfactants can disrupt existing native microgels, converting large assemblies into smaller particles. One possible mechanisms is that surfactants are able to enhance the stability of DOC polymers and disrupt aggregates due to their surface charges and protein-denaturing activities. These findings suggest that the ecological system is altered by anthropogenic surfactants, and provide useful information for ecological assessments of different types of surfactants and raise warnings about surfactant applications. [ABSTRACT FROM AUTHOR]

Soil enzyme activities are sensitive indicators of soil organic matter (SOM) dynamics brought about by climate change. The distribution of soil enzyme activities in wetlands from different types of frozen region in Northeast China was evaluated in this paper. The results showed that the specific enzyme activities of P-glucosidase, invertase, dehydrogenase, urease, and acid phosphatase showed the highest values in seasonally frozen ground indicating faster turnover rate of SOM. Specific activities of invertase and acid phosphatase were higher in discontinuous permafrost than in continuous permafrost. The temperature, SOM and vegetation species regulated soil enzyme activities. Soil dehydrogenase and urease activities increased with soil MBC (microbial biomass carbon) concentrations. p-Glucosidase and acid phosphatase activities were significantly related to DOC (dissolved organic carbon) concentrations suggesting that these two enzymes drive the release of labile components from the SOM. This study helps better understanding relations between soil enzyme and soil labile carbon fractions, and further facilitates the understanding of the stability of soil carbon pool in permafrost wetland of Northeast China. [ABSTRACT FROM AUTHOR]

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

Although macroalgae are regarded as the emerging fourth category of "blue carbon", few studies are available on the dynamics of dissolved organic carbon (DOC) release. Sargassum thunbergii is a typical intertidal macroalgae; and tidal action usually triggers instantaneous changes in temperature, light and salinity. Therefore, we investigated the mechanism of short-term changes in temperature, light and salinity on DOC release by S. thunbergii. As well as these factors coupled with desiccation, the combined effect of DOC release was revealed. The results showed the DOC release rate of S. thunbergii was from 0.028 to 0.037 mg C g −1(FW) h−1 under different photosynthetically active radiation (PAR, 0–1500 μmol photons m−2 s−1). The DOC release rate of S. thunbergii was from 0.008 to 0.208 mg C g −1(FW) h−1 under different salinity (5–40). The DOC release rate of S. thunbergii was from 0.031 to 0.034 mg C g −1(FW) h−1 under different temperature (10–30 °C). Either the increase in intracellular organic matter concentration due to increased photosynthesis (change in PAR and temperature, active), cell dehydration due to dry-out process (passive) or the decrease in extracellular salt concentration (passive) would lead to an increase in the difference in osmotic pressure and promote DOC release. • A flow-through algal carbon fixation capacity measurement system was designed. • The measuring system has four advantages for carbon flux studies. • Short-term changes in light intensity and salinity can affect DOC release. • The difference in osmotic pressure may be the driving force for DOC release. • This work can provide a reference for the study of carbon sinks in macroalgae. [ABSTRACT FROM AUTHOR]

Benthic foraminifera assemblages, nutrient dynamics of surface and porewater from 10 intertidal sites spanning over two years (2019–2020) covering two major estuaries in Sundarbans mangrove were evaluated to understand role of seasonal precipitation and primary production (driven by eddy nutrients) with a focus on standing crop. Benthic foraminifera abundance ranged between 280 individuals/10 cc in pre-monsoon (2019), 415 individuals/10 cc in post-monsoon 2019 and 630 individuals/10 cc in post-monsoon (2020). Standing crop was highest in post-monsoon coinciding with eddy nutrients driven stoichiometry and increase in abundance of large diatom cells. Calcareous and agglutinated foraminifer taxa Ammonia sp.1, Quinqueloculina seminulum , Entzia macrescens and Textularia sp. respectively were frequent. Entzia macrescens was found in dense mangrove vegetation sites; exhibited strong relationship with sediment texture and pore water total organic carbon. One of the major findings is mangroves with pneumatophores improves oxygen availability in sediment and leads to an increase in standing crop. [Display omitted] • Eddy driven nutrients increase benthic foraminifera standing crop in post-monsoon. • Oxygen availability influenced by pneumatophores in sediment leads to increase in foraminifera standing crop. • Entzia macrescens showed strong relationship with porewater carbon. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) plays diverse roles in carbon biogeochemical cycles. Here, we explored the link between DOC and p CO 2 using high-performance size-exclusion chromatography (HPSEC) with UV 254 detection and excitation emission matrix (EEM) fluorescence spectroscopy to determine the molecular weight distribution (MW) and the spectral characteristics of DOC, respectively. The relationship between DOC and p CO 2 was investigated in the Poyang Lake wetlands and their adjacent aquatic systems. The results indicated significant spatial variation in the DOC concentrations, MW distributions, and p CO 2 . The DOC concentration was higher in the wetlands than in the rivers and lakes. p CO 2 was high in wetlands in which the dominant vegetation was Phragmites australis , whereas it was low in wetlands in which Carex tristachya was the dominant species. DOC was divided into five fractions according to MW, as follows: super-low MW (SLMW, <1 kDa); low MW (LMW, 1–2.5 kDa); intermediate MW (IMW, 2.5–3.5 kDa); high MW (HMW, 3.5–6 kDa); and super-high MW (SMW, > 40 kDa). Rivers contained high proportions of HMW and extremely low amounts of SLMW, whereas wetlands had relatively high proportions of SLMW. The proportion of SMW (SMW p ) was particularly high in wetlands. We found that p CO 2 significantly positively correlated with the proportion of IMW, and significantly negatively correlated with SMW p . These data improve our understanding of the MW of bioavailable DOC and its conversion to CO 2 . The present results demonstrate that both the content and characteristics of DOC significantly affect p CO 2 . p CO 2 and DOC must be studied further to help understanding the role of the wetland on the regional CO 2 budget. [ABSTRACT FROM AUTHOR]

Zinc is a contaminant of concern in aquatic environments and is a known toxicant to many aquatic organisms. Dissolved organic matter (DOM) is a toxicity modifying factor for zinc and is an important water chemistry parameter. This study investigated the influence of DOM concentration, source, and water pH on the chronic toxicity of zinc to a freshwater microalga, Chlorella sp. The influence of DOM on zinc toxicity was dependent on both concentration and source. In the absence of DOM, the 72-h EC50 was 112 μg Zn.L−1. In the presence of a DOM high in fulvic-like components, zinc toxicity was either slightly decreased (<4-fold increase in EC10s across 15 mg C.L−1 range) or unchanged (minimal difference in EC50s). In the presence of a DOM high in humic-like (aromatic and high molecular weight) components, zinc toxicity was slightly decreased at the EC10 level and strongly increased at the EC50 level. The influence of pH on zinc toxicity was dependent on the source of DOM present in the water. In the presence of DOM high in humic-like components pH did not influence toxicity. In the presence of DOM high in fulvic-like components, pH had a significant effect on EC50 values. Labile zinc (measured by diffusive gradients in thin-films) followed linear relationships with dissolved zinc but could not explain the changes in observed toxicity, with similar DGT-labile zinc relationships shown for the two DOMs despite each DOM influencing toxicity differently. This indicates changes in toxicity may be unrelated to changes in zinc lability. The results suggest that increased toxicity of zinc in the presence of DOM may be due to direct uptake of Zn-DOM complexes. This study highlights the importance of considering DOM source and characteristics when incorporating DOM into water quality guidelines through bioavailability models. [Display omitted] • The influence of DOM on zinc toxicity was dependent on concentration and source. • DOM high in aromatic humic-like components increased zinc toxicity at the EC50 level. • The influence of pH on zinc toxicity was DOM source dependent. • Zinc lability could not explain the observed increases in toxicity in the presence of DOM. [ABSTRACT FROM AUTHOR]

• Extreme rainfall driven rainwater DOC evolution was investigated in megacity. • Content, deposition flux and impacting factors of rainwater DOC were assessed. • DOC was mainly form the emission of municipal waste, agriculture and traffic. • The high level of DOC deposition flux was found due to the extreme rainfall. Air pollution and related wet deposition process (rainfall) caused environmental hazards under the climate change, particularly in urban regions, attracting global concern and challenges. Atmospheric dissolved organic carbon (DOC) deposition is not only the major removal pathway of OC from atmosphere, but also a significant influence factor of urban haze pollution and local climate. Although the significance of DOC deposition to carbon budgets is confirmed, the extreme rainfall influenced OC transfers from the atmosphere to land is poorly understood. This study systematically investigated the rainwater DOC in Beijing during the extreme rainfall period of 2021 to explore its status, source, and flux. The results showed that the rainwater DOC concentration level is close to the Asian and global mean level, while the DOC deposition flux was relatively high due to high rainfall amount and rainfall scouring, and the overall declined trend of DOC concentrations was identified. Source identification revealed that human OC emissions (municipal wastes, agricultural and traffic emission) are the primary sources of DOC, whereas ocean and crust source contributed negligibly. This research clarified the extreme rainfall-driven rainwater DOC dynamics in a megacity and supported the evaluation of global carbon budgets. [ABSTRACT FROM AUTHOR]

Rising concentrations of dissolved organic carbon (DOC) are negatively affecting the water quality in several drinking water reservoirs. The presence of beaver dams can influence surface water quality on a catchment scale. In recent years, beavers have been re-introduced in numerous locations in Central Europe. We investigated whether the presence of beaver dams in the catchment of a German drinking water reservoir impacts DOC quantity and quality in the streams entering the Wehebach reservoir in Germany. By comparing water quality upstream and downstream of beaver dams during three low discharge situations we did not find a significant effect of dams both on DOC quantity and quality. The analysis of long term monitoring data at the gauges showed that beaver dams had a negligible effect on the DOC load to the reservoir. DOC quantity was closely linked to iron concentration in the streams. Co-precipitation with iron minerals was an effective process removing DOC from the stream-water. By analyzing fluorescence excitation emission indices we show that beaver dams did not have a clear effect on DOC quality. We conclude that the presence of beaver dams has only small effects on water quality and is not a problem for water quality in the downstream drinking water reservoir. [ABSTRACT FROM AUTHOR]

With decreases in acid deposition, nitrogen : phosphorus (N:P) ratios in lakes are anticipated to decline, decreasing P limitation of phytoplankton and potentially changing current food web dynamics. This effect could be particularly pronounced in the Adirondack Mountains of New York State, a historic hotspot for effects of acid deposition. In this study, we evaluate spatial patterns of nutrient dynamics in Adirondack lakes and use these to infer potential future temporal trends. We calculated Mann-Kendall tau correlations among total phosphorus ( TP), chlorophyll a, dissolved organic carbon ( DOC), acid neutralizing capacity ( ANC), and nitrate ( NO3−) concentrations in 52 Adirondack Long Term Monitoring ( ALTM) program lakes using samples collected monthly during 2008-2012. We evaluated the hypothesis that decreased atmospheric N and S deposition will decrease P limitation in freshwater ecosystems historically impacted by acidification. We also compared these patterns among lake watershed characteristics (i.e., seepage or lacking a surface outlet, chain drainage, headwater drainage, thin glacial till, medium glacial till). We found that correlations ( P < 0.05) were highly dependent upon the different hydrologic flowpaths of seepage vs. drainage lakes. Differentiations among watershed till depth were also important in determining correlations due to water interaction with surficial geology. Additionally, we found low NO3−: TP (N:P mass) values in seepage lakes (2.0 in winter, 1.9 in summer) compared to chain drainage lakes (169.4 in winter, 49.5 in summer) and headwater drainage lakes (97.0 in winter, 10.9 in summer), implying a high likelihood of future shifts in limitation patterns for seepage lakes. With increasing DOC and decreasing NO3− concentrations coinciding with decreases in acid deposition, there is reason to expect changes in nutrient dynamics in Adirondack lakes. Seepage lakes may become N-limited, while drainage lakes may become less P-limited, both resulting in increased productivity. Long-term measurements of TP and chlorophyll a from the Adirondacks are needed to inform how future decreases in atmospheric N and S deposition will influence the trophic status of lake ecosystems throughout the region. [ABSTRACT FROM AUTHOR]

Mercury (Hg) concentrations in aquatic environments have increased globally, exposing consumers of aquatic organisms to high Hg levels. For both aquatic and terrestrial consumers, exposure to Hg depends on their food sources as well as environmental factors influencing Hg bioavailability. The majority of the research on the transfer of methylmercury (MeHg), a toxic and bioaccumulating form of Hg, between aquatic and terrestrial food webs has focused on terrestrial piscivores. However, a gap exists in our understanding of the factors regulating MeHg bioaccumulation by non-piscivorous terrestrial predators, specifically consumers of adult aquatic insects. Because dissolved organic carbon ( DOC) binds tightly to MeHg, affecting its transport and availability in aquatic food webs, we hypothesized that DOC affects MeHg transfer from stream food webs to terrestrial predators feeding on emerging adult insects. We tested this hypothesis by collecting data over 2 years from 10 low-order streams spanning a broad DOC gradient in the Lake Sunapee watershed in New Hampshire, USA. We found that streamwater MeHg concentration increased linearly with DOC concentration. However, streams with the highest DOC concentrations had emerging stream prey and spiders with lower MeHg concentrations than streams with intermediate DOC concentrations; a pattern that is similar to fish and larval aquatic insects. Furthermore, high MeHg concentrations found in spiders show that MeHg transfer in adult aquatic insects is an overlooked but potentially significant pathway of MeHg bioaccumulation in terrestrial food webs. Our results suggest that although MeHg in water increases with DOC, MeHg concentrations in stream and terrestrial consumers did not consistently increase with increases in streamwater MeHg concentrations. In fact, there was a change from a positive to a negative relationship between aqueous exposure and bioaccumulation at streamwater MeHg concentrations associated with DOC above ~5 mg/L. Thus, our study highlights the importance of stream DOC for MeHg dynamics beyond stream boundaries, and shows that factors modulating MeHg bioavailability in aquatic systems can affect the transfer of MeHg to terrestrial predators via aquatic subsidies. [ABSTRACT FROM AUTHOR]

Understanding the effect of different topographical settings on soil organic carbon (SOC) fractions could help better soil carbon management under hill rice ecosystems. In our study the SOC and its fractions of particulate organic matter (POM), light fraction of organic matter (LFOM), dissolve organic matter (DOC), microbial biomass carbon (MBC) and hot water-soluble carbon (HWC) were investigated for different topological settings under hill rice ecosystems of Ri-Bhoi district, Meghalaya. It was not found specific distribution pattern of SOC and its fractions at different topological settings. However, there was a variation (P < 0.05) of SOC and its fraction content at different topological settings. The highest POM content was noticed at 32% slope of Pyllun and lowest at Paham (32% slope) following with intermountain valley (Boirymbong). The highest content of LFOM and DOC, MBC, HWC were recorded at 6% slope topography and lowest at 32% slope of Paham. The SOC fractions (POM, LFOM, MBC and HWC) were more at the surface soil whereas DOC was found more the subsurface soil. There were significant positive relationships (P <0.01) between SOC and its corresponding fractions including DOC, POM, LFOM and HWC, a negative relationships (P <0.05) were observed between SOC and DOC and MBC in subsurface soil (15-30 cm). The correlation coefficients with SOC decreased in the order of LFOM > POM > HWC > DOC at surface soil and POM > LFOM > HWC at subsurface soil. It is concluded that further study on soil pedogenic properties influenced on SOC distribution is needed to confirm the SOC controlling variables including slope for better SOC management. [ABSTRACT FROM AUTHOR]

Increasing use of carbon nanotubes (CNTs) has led to their introduction into the environment where they can interact with dissolved organic matter (DOM). This study focuses on solution chemistry effects on DOM adsorption/desorption processes by single-walled CNTs (SWCNTs). Our data show that DOM adsorption is controlled by the attachment of DOM molecules to the SWCNTs, and that the initial adsorption rate is dependent on solution parameters. Adsorbed amount of DOM at high ionic strength was limited, possibly due to alterations in SWCNT bundling. Desorption of DOM performed at low pH resulted in additional DOM adsorption, whereas at high pH, adsorbed DOM amount decreased. The extent of desorption conducted at increased ionic strength was dependent on pre-adsorbed DOM concentration: low DOM loading stimulated additional adsorption of DOM, whereas high DOM loading facilitated release of adsorbed DOM. Elevated ionic strength and increased adsorbed amount of DOM reduced the oxidation temperature of the SWCNTs, suggesting that changes in the assembly of the SWCNTs had occurred. Moreover, DOM-coated SWCNTs at increased ionic strength provided fewer sites for atrazine adsorption. This study enhances our understanding of DOM–SWCNT interactions in aqueous systems influenced by rapid changes in salinity, and facilitates potential use of SWCNTs in water-purification technologies. [ABSTRACT FROM AUTHOR]

Extreme weather events affect surface water supplies. Water quality measurements in Central Arizona were used to quantify changes in dissolved organic carbon (DOC) and turbidity following dust storms, floods, and drought-associated wildfires. This article describes specific extreme events, quantifies changes in DOC and turbidity, and discusses the effects of water quality changes on treatment processes and public perceptions of water quality. Study findings show a co-occurrence of some dust storm events (high particulate matter) and increased surface water turbidity, attenuation of high DOC loads following upper watershed storm events, significant increases in total organic carbon and turbidity following severe flooding in 2005, and differing effects of upland and lowland wildfires on water quality. Finally, a means to mitigate these effects on both perceived and actual water quality by integrating information from radar systems, stream gauge readings, and online water quality analyzers is suggested. [ABSTRACT FROM AUTHOR]

Several countries face scarcity of water, particularly in arid and semi-arid countries such as Egypt. Water supply in Egypt is highly dependent on Nile water, which barely provides for human, agriculture, and industrial consumption. Drainage waste water (DWW) is used for agriculture purposes directly or after blending with Nile water (1:1). DWW contains high concentrations of dissolved organic carbon (DOC), which may prohibit its application. A new process to remove DOC was introduced when wastewater was treated for agriculture purposes. The new process is a combination of anode oxidation and Fenton oxidation coagulation (AFC) in which cathode electrodes were separated from anode electrodes by cation and anion exchange membrane (CEM and AEM). Results showed that the removed DOC was enhanced by applying a separated cathode (SC) system. The most influential factor affecting the treatment was Fe(II) dosage. Based on results obtained, a new reactor contains separated cathode in anode oxidation, Fenton oxidation, and Coagulation (SC–AFC) reactor was made. SC–AFC reactor may be used for hydrogen production simultaneously with the removed DOC since it provides high pH in cathode compartment. [ABSTRACT FROM AUTHOR]