1. 题目: Sources of organic matter and tracing of nutrient pollution in the coastal Bay of Bengal
Stable isotopic composition of carbon (δ13CPOM) and nitrogen (δ15NPOM) in the particulate organic matter (POM) is used to identify sources of organic carbon and nutrients using monthly time-series observation in the coastal Bay of Bengal (BoB). The hydrographic structure indicates that the coastal BoB is influenced by coastal upwelling during March–May, advection of peninsular river discharge during June to September and glacial (Ganges) river discharge during October to December due to reversing of East India Coastal Currents (EICC). C/N ratios in POM were mostly higher values than Redfield ratio in the study region indicating possible contribution of terrestrial origin. Enriched δ13CPOM were found during March–May associated with coastal upwelling indicating major contribution of POM from the in situ production while lower values were noticed during June to September followed by October to December indicating influence of terrestrial sources. δ15NPOM displayed strong inverse relation with salinity and linear relation with Chl-a suggesting that anthropogenic nutrients from the land increased coastal phytoplankton biomass. δ15NPOM linearly decreased with increase in distance from the coast and reached to the typical offshore value of 6–6.5‰ indicating that terrestrial nutrients influence was spread up to a distance of 15 to 20 km from the coast in the study region. Our study suggested that coastal waters are influenced by terrestrial/anthropogenic nutrients and its impact can be noticed up to 15 to 20 km from the coast and its impact on Biodiversity Beyond National Jurisdiction may be negligible than hitherto hypothesized.
2. 题目: Differential responses of macroinvertebrate ionomes across experimental N:P gradients in detritus-based headwater streams
3. 题目: Nitrogen composition in furrow irrigated run-off water
Furrow irrigation in cotton growing vertosols is the most preferred method in Australia. After fertilisation, irrigation water interacts with the soil which can dissolve nitrogen (N) compounds into the run-off water. The run-off or tail water that leaves the field is enriched with N and can reduce crop N use efficiency. During 2014−2015 and 2015−2016 N solute concentration in the irrigation water and run-off was measured in a tillage cropping rotation experiment. In the continuous cotton treatments (2014−2015) when urea was broadcast on the surface of furrow irrigated cotton system, 11 % of the applied fertiliser (260 kg N ha−1) was lost from the field in the tail water. Most of the losses from the soil occurred during the first irrigation as nitrate and urea. The irrigation water supplied 10 kg dissolved organic nitrogen (DON) kg N ha−1 to the field. During 2015−2016, when subsurface banding of the urea was used, losses equated to 5 % of applied N, in irrigated continuous cotton treatments. In a second crop treatment, an irrigated maize rotation, the broadcasted urea was leached into the soil by rainfall before a 100 mm irrigation event. The run-off losses were less than the sub surface urea banding and in this treatment were 0.5 % of the applied fertiliser. The study shows that DON-N, NO3-N, NH4-N, Urea-N are dissolved from the soil in cotton production systems and lost to furrow irrigation run-off. This dissolved N maybe denitrified in the cotton irrigation network if the tail water is not reused quickly. The results show that N contributions from irrigation water need to be accounted for overall N budget of the cotton farm to improve the N use efficiency.
4. 题目: Responses of soil enzyme activity and soil organic carbon stability over time after cropland abandonment in different vegetation zones of the Loess Plateau of China
The effects of cropland abandonment on soil enzyme activity and soil organic carbon (SOC) stability, along with the driving factors, are poorly understood. Here, we aimed to systematically and comprehensively evaluate soil enzyme activity, SOC stability, and the associated driving factors in different vegetation zones after cropland abandonment on the Loess Plateau, China. We selected grasslands with different recovery times along a rainfall gradient encompassing the steppe zone (SZ), forest-steppe zone (FSZ), and forest zone (FZ). We measured and compared the changes in soil enzyme activity (saccharase, polyphenol oxidase, urease, phosphatase, and catalase) and SOC stability as a function of recovery time; we also evaluated the relationships between these two parameters. In SZ and FSZ, soil enzyme activity, fractions of oxidizable carbon (including very labile [C1], labile [C2], and less labile [C3]), and the carbon management index (CMI) increased with recovery time, whereas the SOC stability index (SI) decreased. Conversely, in FZ, polyphenol oxidase activity increased linearly, urease and catalase activities decreased linearly, and the change in saccharase activity was represented by a cubic equation regression. SI showed no obvious changes with recovery time, whereas C1, C2, and C3 initially decreased and then increased. Redundancy analysis showed that, in FSZ and FZ, soil enzyme activity, C1, C2, C3, and SI were influenced by vegetation diversity, coverage, and soil nutrient levels. In comparison, in SZ, these parameters were mainly influenced by soil nutrient levels. Soil enzyme activity was strongly correlated with C1 and C3 in SZ and FSZ, but not in FZ. Overall, in SZ and FSZ, soil enzyme activity increased with recovery time, whereas SOC stability decreased. In contrast, both parameters were relatively stable in FZ, which had higher mean annual precipitation and mean annual temperature.
5. 题目: Effects of land-use patterns on soil carbon and nitrogen variations along revegetated hillslopes in the Chinese Loess Plateau
In water-limited areas, revegetation of abandoned croplands may lead to extensive land-use changes and considerable variations on soil carbon (C) and nitrogen (N). However, the impact of land-use patterns (i.e., the spatial combinations of different land-use types) on soil C and N variations following revegetation remains unclear. In this study, we measured soil organic carbon (SOC), total carbon (TC), and total nitrogen (TN) stocks to a depth of 200 cm in grassland (GL), shrubland (SL), young forestland (YF), and mature forestland (MF) under four land-use patterns in a catchment located in the Chinese Loess Plateau. The highest SOC, TC and TN stocks occurred in MF and the lowest was found in GL. Compared to every single land-use type, soil C and N stocks significantly increased under different land-use patterns. The highest SOC stock (6.51 kg m−2) was found in the GL-YF-SL pattern, and the highest TC stock (47.25 kg m−2) and TN stock (0.70 kg m−2) were both observed in the MF-YF pattern. SOC stocks showed significantly positive correlations with TC and TN stocks under different land-use patterns (p < 0.05), except for the GL-MF. The soil C-N interactions were stronger in the MF-SL and GL-YF-SL patterns compared to the GL-MF and MF-SL. Redundancy analysis indicated that the SOC, TC, and TN variations were well explained by aboveground biomass and land-use patterns, with accumulated variance of 41.6% and 54.2% in Axis 1 and Axis 2, respectively. The differences of soil C and N accumulation among land-use patterns were mostly related to different vegetation coverage and the intensity of soil erosion. This study indicates that creating proper spatial distribution of land-use types on hillslopes could benefit soil C and N sequestrations and ecosystem restoration in semi-arid environments.
6. 题目: Chemical modification of tannins from Acacia mearnsii to produce formaldehyde free flocculant
Flocculants and coagulants market is expected to grow in a Compound Annual Growth Rate (CAGR) of 5.9% between 2017 and 2022. The development of non-pollutant coagulants/flocculants aiming to replace conventional ones, usually toxic, has been extensively studied and one alternative is the possibility of obtaining tannin-based flocculants, compounds present in many plants and easily extracted. However, in order to use tannins as flocculants, their cationization is necessary, which is normally accomplished by Mannich reaction that requires formaldehyde addition, a toxic compound. In order to fill a gap in the literature, regarding coagulants/flocculants synthesis through green procedures, this paper aims to synthesize a flocculant from tannins with no use of formaldehyde, and optimize this synthesis through a Central Composite Rotatable Design (CCRD). The optimization variables were ammonium hydroxide (NH4OH) to tannin ratio, in the range of 1:1 to 5:1, and reaction time, in the range of 1 to 4 h The evaluation of the synthesized flocculant samples was accomplished by jar tests using a simulated effluent containing humic acid and the effect of reactant ratio and reaction time used in the synthesis was assessed. The flocculant synthesis methodology proposed on this study showed excellent results regarding turbidity and color removal, since 100% of turbidity removal and 89.9% of color removal were achieved. This novel tannin-based flocculant synthesis methodology is a promising technology to replace conventional coagulants/flocculants, once it is environmentally friendly.
7. 题目: Disturbance mechanisms of lacustrine organic carbon burial: Case study of Cuopu Lake, Southwest China
Lakes are important organic carbon (OC) traps in the global carbon cycle. Recent studies have shown that the rate of OC burial in lacustrine sediments is influenced by factors such as climate change, land-use change, and eutrophication. In this study, we use multiproxy methods to reveal the mechanisms of lacustrine sediment OC burial in an alpine lake (Cuopu Lake), in southwest China. Combined with the dating from 210Pbex and n-alkanes distribution analysis using the Positive Matrix Factorization model, the sedimentary history was divided into five stages: religious activity (the 1840s–1880s), earthquake (the 1880s–1910s), garrison (the 1910s–1960s), transition (the 1960s–1990s), and ecotourism (the 1990s–2010s). During the earthquake stage, OC burial was dominated by terrestrial solids (>40%) and co-precipitated algae (>30%), with a rapid deposition rate (>4 mm a−1) and low OC concentration (<4 mg g−1). During the other stages, when the level of disturbance was relatively low, a change in nutrient conditions either promoted or inhibited plant growth, which influenced the type of buried OC. The contribution of OC derived from combustion sources varied from stage to stage. Severe anthropogenic disturbances have led to a significant increase in nutritional levels in the lake water, leading to an increase in the OC burial rate. Climate change, which leads to changes in temperature and rainfall, did not significantly influence OC burial, whereas nitrogen deposition (and associated ecological changes) was a significant determinant. When the general mechanism is dominant, the total nitrogen to inorganic phosphorus ratio is an effective indicator of OC burial due to its selective promotion of different plant types. In conclusion, our results suggest that lacustrine sediment OC burial is closely linked to physical and anthropogenic factors in Cuopu Lake, as well as similar montane lakes.
8. 题目: Proton uptake behaviors of organic and inorganic matters in biochars prepared under different pyrolytic temperatures
As an important part of biochar, surface functional group is the key interface between biochars and other phases, as well as an essential source of biochar's alkalinity and buffer abilities. However, due to the intricate organic and inorganic structures within biochars, the contribution from organic and inorganic matters to the functional groups remains unknown. In this work, the proton uptake curves were applied to study the functional groups of biochars via titration. Pine needle (PN) derived biochars with low inorganic content was selected for analyzing the organic functional groups variation under different pyrolysis temperatures. While rice straw (RS) derived biochars and the double-acid treated rice straw (DRS) derived biochars were compared for understanding the contributions from inorganic matters. The results indicate that the sorption behavior of proton onto biochars is surface adsorption, and the functional groups variation within PN biochars keeps consistent with reactions happened during pyrolysis. The inorganic matters within RS biochars contributed significantly to the buffering ability of biochars, and it is noteworthy to find that the contribution of inorganic matters of RS350, RS500, and RS700 on the total proton uptake stabilized at 67%, 84%, and 84% in the pH range of 2–8, respectively. As far as we know, this is the first report on separating the proton uptake ability of the organic and inorganic matters for biochars. The study on the interaction between biochars and proton will improve the estimation of the fate of ionizable pollutants, and the differentiation on the organic and inorganic matter contributions would benefit the understanding of biochar organic structures and inorganic structures.
9. 题目: Chemical characteristics and brown carbon chromophores of atmospheric organic aerosols over the Yangtze River channel: a cruise campaign
Organic aerosols (OAs) have important influences on the climatic implications and health effects of atmospheric aerosols. Among the complex OA constituents, brown carbon (BrC) accounts for a substantial mass fraction and is of special interest because of its light‐absorbing properties. In this study, the chemical composition of atmospheric OAs over the middle‐lower Yangtze River (MLYR) channel, as well as the BrC, was investigated during a ship cruise campaign in winter 2015. In total, more than one thousand molecular formulas were determined using a combination of ultra‐high performance liquid chromatography (UHPLC), a diode array detector (DAD), and Orbitrap high‐resolution mass spectrometry (HRMS). Large numbers and enhanced signal abundances for known tracers as well as monocyclic and polycyclic aromatics indicate that biomass burning and fossil combustion are important sources of OAs over the MLYR channel. In addition, thirteen chromophores with strong light absorption, mostly representing established biomass burning tracers, were unambiguously determined by UHPLC/DAD/HRMS and contributed to 35‐37% of the total light absorption of OAs at 290 nm and 58‐70% at 350 nm. Sixty‐three previously identified biomass burning chromophores were also positively identified in the mass spectrometric analysis here but embedded in the humped signal during the spectroscopic analysis. These BrC chromophores exhibit high degrees of unsaturation, suggesting these compounds to be aromatic, nitro‐aromatic, and polycyclic aromatic type of species. Our results highlight the significant influence of biomass burning and fossil combustion on atmospheric OAs over the MLYR channel in the winter, strongly enhancing light‐absorbing properties and decreasing air quality.
10. 题目: Molecular-Level Transformation of Dissolved Organic Matter during Oxidation by Ozone and Hydroxyl Radical
11. 题目: Four-year continuous residual effects of biochar application to a sandy loam soil on crop yield and N2O and NO emissions under maize-wheat rotation
Biochar application has been reported to effectively mitigate N2O emissions and increase crop yield; however, its long-term residual effects remain largely unknown. A four-year field experiment was designed in the North China Plain (NCP) to evaluate the residual effect of biochar on N2O and NO emissions and crop yield under maize-wheat rotation. The study included five treatments: no N fertilization (Control), N fertilizer application (CN), and N fertilizer plus maize-straw biochar application at 3 (NB3), 6 (NB6) and 12 t ha−1 (NB12). Biochar amendment had no effect on maize yield during the four-year rotation, but increased maize grain N uptake by 12.9 − 14.1 % and fertilizer N use efficiency by 13.8 % in the fourth year. Meanwhile, NB12 treatment decreased wheat yield by 11.7 − 15.5 % in each year, except the second, while decreased average wheat yield. Biochar application significantly reduced N2O emissions by 31.5 − 42.4 % during the first maize season, and by 6.9 − 21.3 % in the third and fourth years primarily due to reduction in NH4+ availability for nitrification. Furthermore, this mitigation effect was positively related to soil moisture content and decreased with time after biochar application. Cumulative N2O emissions during the four wheat seasons were 0.25 − 0.85 kg N2O-N ha−1, and only decreased by 8.9 − 9.9 % under biochar amendment in the third and fourth years probably because low soil temperature suppressed N2O production. Biochar addition in the third and fourth years significantly reduced NO emissions by 9.0 − 20.1 % during the maize growing seasons and 10.5 − 19.1 % during the wheat growing seasons, especially under NB6 treatment. The average yield-scaled N2O and NO emissions were lowest in the NB6 treatment during the maize and wheat season. Overall, these findings suggest that 6 t ha−1 is the optimal biochar application rate for reducing N2O/NO emissions and yield-scaled N2O/NO emission under four-year maize-wheat rotation in the NCP.
12. 题目: Organic biogeochemistry in the oxygen-deficient ocean: A review
Oceanic oxygen-deficient zones (ODZs) encompass open ocean and coastal oxygen minimum zones and euxinic marine basins. A primary goal of this review is to demonstrate how new approaches involving lipidomics and genomics are informing how we think about ODZs. There are five parts to the review. First, a brief overview of early investigations of organic geochemistry in ODZs sets the stage for follow-on work. Second, linkages between organic biomarkers and microbial and geochemical processes are described for three key biogeochemical processes that are characteristic of ODZs: (i) oxidation of ammonium by archaea and anammox bacteria; (ii) redox cycles of metals and sulfur; (iii) the methane cycle. Third, three different approaches are presented that make possible comprehensive, integrated views of the biogeochemistry of the Black Sea, as a case study. Fourth, examples of organic biogeochemical results for ODZs in the modern ocean are projected back into the geological past to show that the same processes have been in play for eons. The final section summarizes how chemistry and biology have been combined in investigations in ODZs and concludes with some challenges for future research.
13. 题目: Development of Fluorescence Surrogates to Predict the Ferrate(VI) Oxidation of Pharmaceuticals in Wastewater Effluents
The removal of pharmaceuticals from wastewater effluents is an emerging concern for environmental scientists and engineers. Ferrate(VI) (FeVIO42−, FeVI) is a promising oxidant and the removal of pharmaceuticals from wastewater effluents has been investigated in this study. Firstly, FeVI oxidation of selected pharmaceuticals was examined by determining the apparent second-order rate constants (kapp) in buffer solutions as a function of pH (5.0-9.5). At pH 8.0, kapp of cimetidine, famotidine, nalidixic acid, ronidazole, dimetridazole, tinidazole, and caffeine are (1.6±0.2)×103, (7.8±0.3)×102, 2.6±0.4, 1.7±0.1, 0.9±0.3, 0.2±0.1, and < 0.1 M−1 s−1, respectively. However, kapp could not be directly employed to predict the removal of pharmaceuticals in the effluents due to the inhibited or enhanced effects of effluent organic matters (EfOM). Therefore, an alternative approach of spectroscopic surrogates was investigated since fluorophore was co-degraded with pharmaceuticals in the wastewater effluents. Particularly, the humic-like fluorescent peak correlated well with the pharmaceutical attenuation. The relationship of the reduction of fluorescence and the removal of pharmaceuticals could be described through a universal equation: . The practical utility of the fluorescence surrogate was validated by applying to field samples. Monitoring the changes of the fluorescence surrogate provides a promising, rapid, and inexpensive method for estimating the degradation of pharmaceuticals during FeVI treatment of wastewater effluents.
14. 题目: Impacts induced by the combination of earthworms, residue and tillage on soil organic carbon dynamics using 13C labelling technique and X-ray computed tomography
Soil organic carbon (SOC) plays a key role in soil fertility and atmospheric CO2 concentration. Our previous work found that tillage induced changes in aggregate stability and pore structure were major factors contributing to the effect of tillage system on SOC. Effects of earthworms and residue on SOC vary among tillage practices, but we don't clearly know how earthworms, residue and tillage interact to affect SOC. A further study was carried out by adding 13C labeled maize residue and earthworms to undisturbed soil mesocosms from conventional tillage (CT) and no tillage (NT) plots and then incubating for 180 days at 18 °C. SOC, 13C, and soil aggregate were measured prior to and after incubation and pore structure was measured after incubation. Newly added residue had the same decomposition rate in CT and NT. Earthworms reduced the SOC content in CT, and the newly added residue reduced the SOC in NT. The earthworms increased average pore diameter of >500 μm, and decreased the pore number of 100−500 μm in NT. The newly added residue improved the SOC by increasing the MWD in CT. The earthworms could change the SOC by increasing the volume fraction in NT. This result is helpful in understanding how the earthworms and residue affect the SOC under different tillage practices and provides direction for developing strategies to increase soil fertility and mitigate emission of CO2 to the atmosphere.
15. 题目: De-ashed biochar enhances nitrogen retention in manured soil and changes soil microbial dynamics
Enhancing soil N retention is important to mitigate the negative environmental impacts caused by the loss of applied N fertilizers. Therefore, the use of modified biochar in the soil is a novel approach to enhance the sorption of N ions. Biochars derived from bamboo, cow, and pig manures were de-ashed and their properties were characterized. The de-ashed biochars were comparatively assessed with raw biochars on N-retention, and how this process is regulated by microbial activities, diversity, and abundance in a manured soil. De-ashing increased the intensity of biochar functional groups and their surface structure. In manured soils, the application of de-ashed bamboo biochar (PDBB) and de-ashed cow manure biochar (PDCB) led to an increase in NH4+-N retention of 34.5% and 6.8% relative to the amendment with raw biochars. Similarly, increased retention of 20.9%, 14.8%, and 19.1% of NO3−-N, and an increase of 21.1%, 11.1% and 11.5% in total N were observed in PDBB, PDCB and de-ashed pig manure biochar (PDPB) respectively, compared to their raw biochars after 8 weeks. The modified surface properties of de-ashed biochars led to higher bacterial colonization, with an increase in the diversity and relative abundance of bacterial 16S rRNA genes, compared to the raw biochar treatments. This spike in microbial groups stimulated protease activities and hence, an increased abundance of N-cycling organisms. The increased microbial abundance was associated with a reduction in the release of urease by these microbial groups for the hydrolysis of urea, thereby ensuring soil N retention. De-ashing increased the intensity of biochar functional groups and improved its surface properties, which resulted in increased N-sorption, and immobilization by stimulating microbial activities and diversity in soil.
16. 题目: Application of a new HMW framework derived ANN model for optimization of aquatic dissolved organic matter removal by coagulation
Removing dissolved organic matter (DOM) with polyaluminium chloride is one of the primary goals of drinking water treatment. In this study, a new HMW framework was proposed, which divided the factors affecting coagulation into three parts consisting of hydraulic condition (H), metal salt (M), and background water matrix (W). In this framework, H, M and W were assumed to be interacted with each other and combined to determine coagulation efficiency. We investigated the feasibility of the framework to determine the treatment efficiency through mathematical models. Results showed that non-linear artificial neural network (ANN) model was a better fit to the experimental data than the linear partial least squares (PLS) model: the ANN model could explain 76% of the total variations while the PLS could only explain 71%. The PLS did not follow the variations of observed values adequately. These experiments showed that the interaction between the HMW framework components were not simple linear relationships. The ANN model was able to optimize the composition of the HMW framework improving the efficiency of DOM removal through the components of HMW such as velocity gradient (G value), coagulant dosage, solution pH, and background water matrix. Overall, HMW framework is a new classification of factors affecting coagulation, leading to a better understanding of the coagulation process and sensitivity to influencing variables.
17. 题目: Alkaline-thermal pretreatment of spectinomycin mycelial residues: Insights on anaerobic biodegradability and the fate of antibiotic resistance genes
Alkaline-thermal (AT) pretreatment is an economical and efficient pretreatment method to improve anaerobic biodegradability of biowaste. This study investigated the effect of AT pretreatment of spectinomycin mycelial residues (SMRs) for promoting anaerobic biodegradability along with the reduction of antibiotic resistance genes (ARGs), and thus obtained the optimal conditions of AT pretreatment. Biomethane potential (BMP) test was conducted to evaluate the anaerobic biodegradability of untreated and pretreated SMRs, and the fate of ARGs was tracked by quantitative polymerase chain reaction. Results showed that the modified Gompertz model fitted the results of BMP tests satisfactorily. Furthermore, AT pretreatment promoted BMP (B0) and reduced lag phase (λ) effectively. These were attributed to the solubilization of SMRs. The analyses of the changes in dissolved organic matter indicated that AT pretreatment could facilitate the solubilization of both biodegradable (e.g. protein) and recalcitrant matter (e.g. humic-like, analyzing by EEMs-PARAFAC), which had a significant corresponding positive (Person correlation, p < 0.01) and negative (Partial correlation, p < 0.01) influences on anaerobic biodegradability. However, the positive effects surpassed the negative effects, promoting the overall anaerobic biodegradability of SMRs. In addition, a considerable reduction of ARGs (by 0.62∼1.36 log units) was observed at pH ≥ 12, attributed to the hydrolysis of phosphodiester bond of DNA in strong alkaline solution. Considering both anaerobic biodegradability and ARGs, the optimal AT condition was concluded as pH 12, temperature 90 oC and time 120 min.
18. 题目: Fe-doped biochar derived from waste sludge for degradation of rhodamine B via enhancing activation of peroxymonosulfate
The disposal and management of waste sludge is a considerable challenge for environmental protection and resource utilization. Herein, sludge-based biochar material loaded with nano-Fe3O4 () was fabricated via hydrothermal carbonization process and employed as catalyst to activate peroxymonosulfate (PMS) for degrading organic dyes in wastewater. Benefiting from the proper iron content, porous structure and the good dispersibility of iron on the catalyst surface, the proposed catalyst not only exhibited excellent catalytic activity and durability in the activation of PMS to degrade Rhodamine B (RhB), which was almost completely removed in 10 min (50 mL 50 mg L−1), but also performed broad application prospects in pollutant degradation. More importantly, the free radical quenching test and electron spin-resonance spectroscopy (ESR) detection demonstrated that O2•-, SO4•-, OH and 1O2 were generated during the process of catalyst activation of PMS. Based on this, a possible reaction pathway for degrading RhB with the aid of was put forward. It is believed that this work offers a promising reuse method of converting the waste sludge to a high efficiency and low-cost nano magnetic catalyst to activate PMS for degrading refractory organic pollutants in aquatic surroundings.
19. 题目: Electron donating capacities of DOM model compounds and their relationships with chlorine demand, byproduct formation, and other properties in chlorination
Electron donating capacity (EDC) is a promising parameter to characterize the antioxidant properties and oxidant consumption of dissolved organic matter (DOM). To assess the potential of EDC in rapidly predicting the chlorine demand during chlorination, the EDC values were measured for ten DOM model compounds, including phenol, quinol, resorcinol, vanillin, tannic acid, l-phenylalanine, l-tryptophan, l-tyrosine, l-cysteine, and reduced glutathione. The EDC values varied according to the functional moieties present in the model compounds and the pH. At pH 7.0, the order of EDC values of the ten model compounds was (mol e−/mol C): 0.843 (cysteine) > 0.538 (tyrosine) > 0.522 (tannic acid) > 0.516 (resorcinol) > 0.452 (phenol) ≈ 0.450 (tryptophan) > 0.257 (vanillin) > 0.226 (reduced glutathione) > 0.160 (quinol) > 0.00035 (phenylalanine). The EDC values correlated well (R2 = 0.93) with the 24 h Cl2 demand of the model compounds (except for phenol and tannic acid). By contrast, there was poor correlation between the EDC values and the 24 h formation potentials of chlorination byproducts (trihalomethanes, haloacetic acids and haloacetonitriles). The levels and variation of the EDC values were not significantly correlated with the total organic carbon, specific UV absorbance at 254 nm, or assimilable organic carbon of the model compounds.
20. 题目: Effects of non‐native fish on lacustrine food web structure and mercury biomagnification along a dissolved organic carbon gradient
Though the introduction of non‐native fish species has been shown to alter trophic ecology in aquatic ecosystems, there has been limited research on how invasive species alter methylmercury (MeHg) biomagnification in lacustrine food webs. We sampled surface water and biota from eight lakes in Quebec, Canada, spanning a range of dissolved organic carbon (DOC) concentrations (2.9 to 8.4 mg/L); four lakes were inhabited by native brook trout (Salvelinus fontinalis ) and the remaining lakes contained brook trout and a non‐native fish, Allegheny pearl dace (Margariscus margarita ). Periphyton, zooplankton, macroinvertebrates, and fish were analyzed for: 1) stable carbon (δ13C) and nitrogen (δ15N) isotope ratios to delineate food webs, and 2) total Hg (THg) or MeHg. Compared to the brook trout from reference lakes, fish from invaded lakes had higher length‐standardized THg concentrations as well as a narrower dietary range and elevated trophic level, inferred from unadjusted δ13C and δ15N values, respectively. The rate of Hg biomagnification was similar across invaded and reference lakes, implying little effect of the invasive fish on the trophic transfer of MeHg. Despite differences in food web structure due to pearl dace invasion, DOC was the strongest predictor of brook trout THg levels for all lakes, suggesting that underlying environmental factors exerted a stronger influence on brook trout THg concentrations than the presence of a non‐native forage fish.
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