Effects of microbial-converted ancient permafrost organic carbon on the growth and reproduction of Daphnia magna.

Immense amounts of ancient (radiocarbon age over 200 years) organic carbon (OC) from permafrost are released into aquatic systems. Ancient terrestrial OC exists in numerous aquatic ecosystems. It has been reported that ancient OC can be incorporated by consumers in aquatic ecosystems, but the effect of ancient OC on the growth of consumers has rarely been studied. In this study, we extracted ancient dissolved organic carbon (DOC) from frozen soils in an alpine lake catchment. After a 6-day microbial conversion period, the contents of ω3 and ω6 polyunsaturated fatty acids (PUFAs) in ancient DOC increased. Proteobacteria and Actinobacteria were the primary taxa consuming the permafrost DOC and generating fatty acids. In addition to the exclusive diet of soil DOC (containing bacteria) or Chlorella pyrenoidosa, mixed diets of Chlorella pyrenoidosa, and ancient DOC (containing bacteria) in ratios of 2:1, 1:1, and 1:2 (by carbon concentration) were used to feed Daphnia magna. We discovered that Daphnia reared on the mixture with the DOC:Chlorella ratio of 1:2 had the highest contents of ω3 PUFAs and FAs. Daphnia reared exclusively on Chlorella and the mixture with the DOC:Chlorella ratio of 1:2 had the largest body size (3.1-3.4 mm) and the highest offspring production (95.5-96.2 ind-1). Daphnia fed on mixed diets exhibited higher intrinsic rates of population growth (0.48-0.53 d-1) compared to those fed exclusively on Chlorella pyrenoidosa, or ancient DOC plus bacteria. Overall, ancient soil OC converted by bacteria can act as a valuable supplement to algae food to promote Daphnia growth.

Two-dimensional, high-resolution imaging of pH dynamics in the phyllosphere of submerged macrophyte using a new Nano-optode.

The phyllosphere pH helps shape the plant microbiome and strongly influences aboveground interactions in plant canopies. Yet little is known about the distribution of pH at a microscale within the macrophyte phyllosphere and the factors promoting them because achieving high-resolution quantitative imaging of phyllosphere pH is a great challenge. Here, new ratiometric pH nano-optodes were prepared by firstly encapsulating the self-synthesized lipophilic dyes (8-acetoxypyrene-N1, N3, N6-trioctadecyl-1, 3, 6-tri-trisulfonamide) to poly(1-vinylpyrrolidone-co-styrene) nanoparticles, and then immobilizing the resulting nanoparticles in polyurethane hydrogel on transparent foils. The nano-optodes presented reversible and fast response (t95 < 80 s) to the pH range from 7.0 to 11.0, with merits of good spatial resolution, photobleaching/leaching resistance and negligible cross-sensitives toward temperature, O2 and ionic strength (< 100 mM). The nano-optodes together with a self-designed phyllosphere chamber were further applied to directly measure the pH distributions at a microscale around single leaves of V. spiralis grown in natural sediment. The pronounced pH microheterogeneity and leaf basification within the V. spiralis phyllosphere were quantitatively visualized. We also provided direct empirical evidence that the dynamic of the phyllosphere pH at high resolution was significantly controlled by the shifting light intensity and temperature. Implementation of the nano-optodes holds great potential for various laboratory applications, which will provide an in-depth insight into phyllosphere activities on the microscale.

A Novel Fluorescent Probe Strategy Activated by ß-Glucuronidase for Assisting Surgical Resection of Liver Cancer.

Liver cancer is a primary malignant tumor with a very high fatality rate, which has seriously threatened human health and life. In normal hepatocellular lesions, ß-glucuronidase (GLU) activity in liver cancer tissues is significantly increased. Therefore, GLU has become one of the important biomarkers of primary liver cancer. Here, a series of fluorescent probes (DCDH, DCDCH3, DCDOCH3, and DCDNO2) for early diagnosis of liver cancer and auxiliary surgical resection were successfully synthesized. Since the electron-withdrawing group -NO2 connected to the probe DCDNO2 accelerates the rapid cleavage of the glycosidic bond, DCDNO2 exhibits superior fluorescence properties that are more sensitive and rapid than the other three probes DCDH, DCDCH3, and DCDOCH3 when detecting GLU. DCDNO2 has been well-applied in real-time fluorescent visualization imaging for the detection of GLU activity in liver cancer cells and tumor tissues. In addition, DCDNO2 has also been successfully used in the early diagnosis of liver cancer and real-time imaging to guide the surgical resection of liver cancer tumors. Therefore, DCDNO2 has great potential for development in bioclinical medicine for the early detection and treatment of liver cancer.

Muscle Mass Measurement Using Machine Learning Algorithms with Electrical Impedance Myography.

Sarcopenia is a wild chronic disease among elderly people. Although it does not entail a life-threatening risk, it will increase the adverse risk due to the associated unsteady gait, fall, fractures, and functional disability. The import factors in diagnosing sarcopenia are muscle mass and strength. The examination of muscle mass must be carried in the clinic. However, the loss of muscle mass can be improved by rehabilitation that can be performed in non-medical environments. Electronic impedance myography (EIM) can measure some parameters of muscles that have the correlations with muscle mass and strength. The goal of this study is to use machine learning algorithms to estimate the total mass of thigh muscles (MoTM) with the parameters of EIM and body information. We explored the seven major muscles of lower limbs. The feature selection methods, including recursive feature elimination (RFE) and feature combination, were used to select the optimal features based on the ridge regression (RR) and support vector regression (SVR) models. The optimal features were the resistance of rectus femoris normalized by the thigh circumference, phase of tibialis anterior combined with the gender, and body information, height, and weight. There were 96 subjects involved in this study. The performances of estimating the MoTM used the regression coefficient (r2) and root-mean-square error (RMSE), which were 0.800 and 0.929, and 1.432 kg and 0.980 kg for RR and SVR models, respectively. Thus, the proposed method could have the potential to support people examining their muscle mass in non-medical environments.

Does ancient permafrost-derived organic carbon affect lake zooplankton growth? An experimental study on Daphnia magna.

The popular paradigm in trophic dynamic theory is that contemporary autochthonous organic matter (e.g., phytoplankton) sustains consumer growth, whereas aged allochthonous organic matter is conceptually considered recalcitrant resources that may only be used to support consumer respiration but suppress consumer growth. This resource-age paradigm has been challenged by a growing body of recent evidence that ancient (radiocarbon depleted) organic carbon (OC) released from glaciers and permafrost can be incorporated by consumers in aquatic systems. However, little information is available regarding the food quality of ancient terrestrial OC and how it impacts the growth of consumers in lakes. Here, ancient dissolved organic carbon (DOC) was extracted from frozen soils in an alpine lake catchment. The contents of polyunsaturated fatty acids (PUFAs) in soil DOC increased significantly after bioconversion by heterotrophic bacteria. The utilization of soil DOC by heterotrophic bacteria also increased the total phosphorus concentration in the systems. Gammaproteobacteria and Betaproteobacteria showed a strong negative correlation with the percentage contents of fluorescent components, including humic-like and tyrosine-like components. Daphnia magna were fed Auxenochlorella vulgaris and ancient DOC plus heterotrophic bacteria. The contents of PUFAs and the growth of zooplankton were influenced by the pre-conversion time of ancient DOC by bacteria. When ancient DOC was pre-converted by bacteria for 27 days, D. magna fed on the mixed diets showed the highest body length (3.40 mm) and intrinsic rate of increase in population (0.49 d-1). Our findings provide direct evidence that ancient terrestrial OC can be an important subsidy for lake secondary production, which have important implications for food webs in high-altitude and polar lakes.

The Light-to-Nutrient Ratio in Alpine Lakes: Different Scenarios of Bacterial Nutrient Limitation and Community Structure in Lakes Above and Below the Treeline.

The light-to-nutrient hypothesis proposes that under high light-to-nutrient conditions, bacteria tend to be limited by phosphorus (P), while under relatively low light-to-nutrient conditions, bacteria are likely driven towards carbon (C) limitation. Exploring whether this light-to-nutrient hypothesis is fitting for alpine lakes has profound implications for predicting the impacts of climatic and environmental changes on the structures and processes of aquatic ecosystems in climate-sensitive regions. We investigated the environmental conditions and bacterioplankton community compositions of 15 high-elevation lakes (7 above and 8 below treeline). High light-to-nutrient conditions (denoted by the reciprocal value of the attenuation coefficient (1/K) to total phosphorus (TP)), high chlorophyll a (Chl a) concentrations, low TP concentrations and low ratios of the dissolved organic carbon concentration to the dissolved total nitrogen concentration (DOC:DTN) were detected in above-treeline lakes. Significant positive correlations between the bacterioplankton community compositions with 1/K:TP ratios and Chl a concentrations indicated that not only high light energy but also nutrient competition between phytoplankton and bacteria could induce P limitation for bacteria. In contrast, low light-to-nutrient conditions and high allochthonous DOC input in below-treeline lakes lessen P limitation and C limitation. The most abundant genus, Polynucleobacter, was significantly enriched, and more diverse oligotypes of Polynucleobacter operational taxonomic units were identified in the below-treeline lakes, indicating the divergence of niche adaptations among Polynucleobacter oligotypes. The discrepancies in the light-to-P ratio and the components of organic matter between the above-treeline and below-treeline lakes have important implications for the nutrient limitation of bacterioplankton and their community compositions.

Bacterial abundance and community structure in response to nutrients and photodegraded terrestrial humic acids in a eutrophic lake.

The exposure of humic substances to solar radiation can alter their concentration and composition and subsequently influences their bioavailability in aquatic food webs. With eutrophication increasingly prominent in lakes, nutrients, such as inorganic N and P, are a prerequisite for heterotrophic bacteria that use organic matter. Here photodegradation of terrestrial humic acids and nutrient addition were performed to investigate the response of bacterial abundance and community structure to photodegraded humic acids and increased nutrient concentrations in a eutrophic lake. Results showed that the decreasing level of absorption coefficient at 460 nm in the treatment irradiated with 40 W UV lamps was more remarkable than that of the treatment irradiated with 20 W UV lamps and the control. This reduced coefficient corresponds to the greatest decrease in humic acid concentration in the 40 W group. Bacteria showed high abundance after incubation with humic acids which underwent strong irradiation intensity. An increased nutrient concentration significantly affected bacterial abundance. The dominant bacteria were Aquabacterium for the irradiated group, Aquabacterium and Limnobacter for the 20 W group and Flavobacterium and Limnobacter for the 40 W group. Armatimonadetes-gp4 and Sediminibacterium showed evident response to high nutrient concentration. Our results showed that the exposure of terrestrial humic acids to UV light and the increasing concentration of nutrients have obviously changed bacterial community.

Fabrication of bacteriochlorin shell/gold core nanoparticles for the sensitive determination of trichlosan using differential pulse voltammetry.

The triclosan contamination in daily life has attracted great attention, and there is rare electroanalytical assay based on π-system dyes. In this work, a facile preparation and electroanalytical application of an organic dispersion containing bacteriochlorin dyes (LS11) and gold nanoparticles (AuNPs) was proposed. The organic-inorganic hybrid nanocomposites were characterized by transmission electron microscope (TEM) showing a core-shell structure with a uniform layer of dye molecules. The as-prepared nanocomposites were successfully coated onto glassy carbon electrodes, and the surface characteristics of the top most layer of the modified electrodes were examined by atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and water contact angle experiments. The nanocomposite film-modified electrodes exhibited good electrochemical activity towards oxidation of triclosan. The oxidation of adsorbed triclosan occurred at a reduced overpotential, and the anodic current responses under a pre-concentration step prior to the potential scan were used for quantitative analysis. A good linear relationship from 0.01 µM to 0.5 µM was obtained using differential pulse voltammetry. The sensitivity and detection limit (S/N = 3) were 23.69 µA µM-1 and 0.03 µM, respectively. The proposed assay was applied to detect triclosan in two personal hygiene products using standard addition method, and the results showed good recoveries that ranged from 96.6% to 101.5% and from 99.3% to 103.8% for a toothpaste sample and a hand wash sample, respectively. A reference HPLC-UV method was used to evaluate the proposed electroanalytical method, and a good agreement was achieved.

Photogeneration and steady-state concentration of hydroxyl radical in river and lake waters along middle-lower Yangtze region, China.

Hydroxyl radical (HO∙) in natural waters plays a critical role in contaminant transformation and ecosystem health. In this study, the photogeneration and steady-state concentration of HO∙ in different aquatic environments (e.g., river and lake) along the middle-lower Yangtze region, China, were evaluated. The results showed that, compared to lake samples, the river waters were characterized by lower HO∙ photoformation rate (RHO∙) (5.10-11.69 × 10-11 vs. 1.10-1.82 × 10-10 M s-1) and steady-state HO∙ concentration ([HO∙]) (1.76-3.11 × 10-17 vs. 2.50-10.33 × 10-17 M). The contribution of nitrate and nitrite to the total RHO∙ in river waters was generally higher than that in lake waters, and photolysis of nitrite exhibited contributions 1-2 times higher than those of nitrate (0-25% vs. 0-9%) irrespective of sample types. As a result, the photosensitization by chromophoric dissolved organic matter (CDOM) contributed more than 70% of the total RHO∙ for all samples except for River Ganjiang. [HO∙] among all samples was positively correlated with dissolved organic carbon (DOC) concentration, and the DOC-normalized [HO∙] was further related to the physicochemical properties of CDOM samples (e.g., aromaticity, humification, and molecular weight). The humic-like aromatic substances with low molecular weight were the controlling factors influencing [HO∙] in the studied surface waters. The results contributed to a deeper understanding of behaviors and fate of aquatic DOMs in terms of HO∙ formation and contaminant attenuation.

Long-term changes of water quality in aquaculture-dominated lakes as revealed by sediment geochemical records in Lake Taibai (Eastern China).

The rapid development and exploitation of the Yangtze River basin in order to ensure human food security and increase living space in recent decades has resulted in significant potential for degradation of water quality in the river and in hundreds of lakes. Understanding how lake environments have evolved to their present state under a variety of external influences is crucial for evaluating their current status and anticipating future scenarios of environmental changes. However, the lakes along the middle reaches of the Yangtze River (MRY) are as yet little studied. Here, we described the long-term anthropogenic environmental transformations of a small lake (Lake Taibai) in the MRY area, based on a detailed quantitative geochemical analysis of the aliphatic hydrocarbons, nutrients (N and P), biogenic silica (BSi), and major and trace elements present in a dated sediment core retrieved from the lake. Our data revealed that levels of short-chain n-alkanes, αß-hopanes and the trace elements arsenic (As) and cadmium (Cd) were all low for the entire record in sediments prior to ca. 1970, reflecting unpolluted natural state of the lake. Pronounced anthropogenic effects began to appear in sediments deposited in the subsequent years ca. 1970-1990, during which the levels of all these components were elevated, most likely driven by input of nitrogen (N) and phosphorus (P) containing chemical fertilizers, pesticides and diesel oil respectively. Since ca. 1990, changes of short-chain n-alkane levels in the sediment suggested the lake had undergone dramatic eutrophication in which existing anthropogenic stressors were exacerbated by technological advances that extended the use of chemical fertilizer into aquaculture. This pattern contrasted with an otherwise comparable lake in the lower Yangtze River basin, Lake Changdang, in which trace element and petroleum pollution were much more prominent due to dramatic urbanization and industrialization of the catchment.

Anthropogenically driven differences in n-alkane distributions of surface sediments from 19 lakes along the middle Yangtze River, Eastern China.

During the past few decades, the Yangtze River basin has undergone massive anthropogenic change. In order to evaluate the impacts of human interventions on sediment n-alkanes of lakes across this region, the aliphatic hydrocarbon fractions of 19 surface sediment samples collected from lakes along the middle reaches of the Yangtze River (MYR) were analyzed using gas chromatography-mass spectrometry. The n-alkanes extracted from the sediments contained a homologous series from C15 to C34, with a notable predominance of odd carbon compounds except for sediments from the more intensively industrialized Lake Daye, in which > C21 n-alkanes showed no odd/even predominance, and carbon preference index (CPI) approached unity. Abundance values of middle-chain (C21, C23, and C25) and long-chain (C27, C29, C31, and C33) n-alkanes in Lake Daye were approximately 4 to 3 times greater than the average for other lakes, reaching 272.4 and 486.3 µg/g TOC, respectively, in the study. Short-chain n-alkanes (C15, C17, and C19) in the sediments varied in abundance from 10.0 to 76.2 µg/g TOC across the study and showed a moderate correlation with total phosphorus (TP) concentrations in the overlying water. The results indicated anthropogenic eutrophication enhanced the accumulation of short-chain n-alkanes in sediments because the primary producers in which they are synthesized are highly susceptible to nutrient forcing. Middle-chain n-alkane abundances were less affected by eutrophication and generally enriched in macrophyte lakes, while long-chain n-alkanes tend to be low in sediments from more eutrophic water. In the case of Lake Daye, direct discharges of petroleum products from heavy industry have introduced quantities of petroleum n-alkanes (> C21), far exceeding the amounts of biogenic input, and the sediment > C21 n-alkanes detected in this study showed typical characteristics of petroleum source. In other lakes, inputs of petroleum products from surface runoff of vehicle/traffic emissions associated with urbanization and economic growth contributed comparatively few n-alkanes to sediments, resulting in declines in CPI for > C21 n-alkanes, most obviously in Lakes Huanggai, Donghu, and Futou. Calculated CPI values suggest that a major proportion of the n-alkanes present in these lakes are derived from biogenic input. The results of this study provided evidences that n-alkane profiles of lake sediments respond sensitively to human-induced eutrophication and different sources of petroleum pollution.

Formation of organosilica nanoparticles with dual functional groups and simultaneous payload entrapment.

A mixed organosilane system for simultaneous formation of organosilica nanoparticles has been systematically studied for loading of various compounds with a wide range of log P values. The molecule-entrapping system was understood by investigating the effects of adjusting various experimental parameters on particle formation and molecule entrapment. Particularly, rhodamine 6 G (R6G) loaded colloidal particles were prepared and characterised in detail. The results show that whereas most molecules had entrapment efficiency (EE%) in the range of 20-80%, R6G exhibited near 100% efficiency. Moreover, the colloidal system can be tuned to incorporate R6G with the extent of entrapment spanning at least 2 orders of magnitude (i.e. from 0.04 to 4 mg) and a maximum EE% of 98%. In conclusion, the study demonstrates the promise of the proposed mixed organosilane system in forming colloidal particles containing multiple functional groups with selective loading of highly hydrophobic molecules.

Nanocarbon material-supported conducting poly(melamine) nanoparticle-modified screen-printed carbon electrodes for highly sensitive determination of nitrofuran drugs by adsorptive stripping voltammetry.

The toxicity of nitrofuran drugs has attracted great attention, and the reported electroanalytical methods suffered limited sensitivity. In this work, a sensitive electrochemical assay in the cathodic region is developed to determine four nitrofuran derivatives, including nitrofurantoin (NFT), nitrofurazone (NFZ), furaltadone (FTD), and furazolidone (FZD). The screen-printed carbon electrode (SPCE) was used as the electrode substrate, and the sensing surface was composed of multi-walled carbon nanotube (MWCNT) and conducting poly(melamine) (PME). The overoxidation-pretreated MWCNTs affect the surface morphology of the electrodeposited PME and, thus, the interaction with nitrofuran drugs. The characteristics of the nanocomposite-modified electrode surfaces were well characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and surface water contact angle experiments. The nanocomposite-modified electrodes exhibited excellent adsorption and electrochemical reduction of nitrofurans by cyclic voltammetry. The proposed assay exhibited a linear range of sub-micro to micro molar concentrations for the four drugs under the optimized differential pulse voltammetric (DPV) technique. The detection limits were found to be in the nanomolar ranges. The developed assay was applied to detect NFT in two real samples, and the results showed good recoveries that ranged from 99.0 to 104.8% and 98.0 to 103.2% for milk and lake water samples, respectively. Graphical abstract ᅟ.

A novel electroanalytical assay for sulfamethazine determination in food samples based on conducting polymer nanocomposite-modified electrodes.

The toxicity of sulfa drugs has attracted great attention, and the reported electrochemical methods for sulfa drugs usually employ a high oxidation potential. In this work, a one-pot synthesized conducting polymer nanocomposite containing poly(3,4-ethylenedioxythiophene) (PEDOT) and MnO2 was cast on a screen-printed carbon electrode (SPCE), and the modified electrode showed superior electrochemical activity over a bare electrode for sulfamethazine (SMZ) determination. The SMZ detection was based on the electrochemical oxidation product, which showed an adsorptive property and exhibited a redox couple at 0.39V in pH 3 phosphate buffer solutions (PBS). The electrode surfaces were well characterized by the water contact angle technique, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM) and cyclic voltammetry. By the use of square wave voltammetry (SWV), a wide linear response to SMZ, from 1.0µM to 500µM, was obtained. The sensitivity and detection limits (S/N = 3) were 0.115µAµM-1 and 0.16µM, respectively. The proposed method and a reference high-performance liquid chromatographic method (HPLC) were applied for the determination of SMZ in two real samples using the standard addition method, and satisfactory recoveries and good agreement were obtained.

Sedimentary lipid biomarker record of human-induced environmental change during the past century in Lake Changdang, Lake Taihu basin, Eastern China.

During the past hundred years, the Lake Taihu basin has been greatly impacted by human interventions. The undesirable changes in water quality of lakes, presumably caused by the human activities, remain relatively undescribed in this area. In order to investigate these anthropogenic effects, a 210Pb dated sediment core from a relatively small lake in the upper reaches of Lake Taihu known as Lake Changdang was subject to a detailed lipid biomarker study and other geochemical analyses including quantification of biogenic silica (BSi), nutrients and heavy metals. Based on the results, the recent environmental history of Lake Changdang can be divided into three periods. The first period from approximately 1906 to 1950, represents a natural state, with minimal anthropogenic impact on the lake. Human induced environmental change is recorded in the following stage, ca. 1950-1982, during which the trophic status of the lake increased slightly in response to inputs of agricultural waste and nitrogen (N) and phosphorus (P) based fertilizers. In particular, the signs of eutrophication during this phase accelerated from ca. 1973, perhaps owing to large-scale using phosphate based chemical fertilizer around the lake at the time. A second phase of nutrient input in the most recent stage, ca. from 1982 to 2016, initiated by wastewater discharge from rapid urbanization and industrialization of the catchment, greatly enhanced the nutrient level in the lake. However, the central zone of the lake has yet to reach a phytoplankton-dominated stable state, with both algae and aquatic macrophytes tracking an increased trend in productivity driven by intermediate nutrient levels in the water of this zone.

Sediment lipid biomarkers record phytoplankton dynamics of Lake Heihai (Yunnan Province, SW China) driven by climate warming since the 1980s.

Increased phosphorus (P) export from sediments to the overlying water column is a significant factor driving the variation of phytoplankton in productivity and community structure in lakes. However, the lack of long-term instrumental data often impeded analyses attempting to associate dynamics of phytoplankton with variation of internal P loading. Here, elements and lipid biomarkers were analyzed in a sediment core from Lake Heihai, a small, deep, and ultraoligotrophic alpine lake in Haba Mountain, Yunnan Province, SW China. The data document incredible enrichment of element iron (Fe) in the sediment, whose concentrations are much higher than those of other common major elements including titanium (Ti), aluminum (Al), calcium (Ca), and magnesium (Mg). This finding, together with the abundance correlation between P and Fe (n = 30, R 2  = 0.783) suggested that P was probably retained in sediments through sorption with micro-layer of FeOOH at the sediment-water interface. The P/Ti ratios, P/Fe ratios, and P/total organic carbon (TOC) ratios all declined in the sediment since 1980, perhaps indicating increased P release from sediments to the overlying water column initiated by hypolimnion anoxia and sulfidic, which is presumably triggered by regional climate warming since the 1980s. The P-rich bottom water can be injected into photic zone during wind-driven mixing and overturn of the water column, although its frequency and intensity might decline due to stronger water column stratification in warming climate. In response, diatoms exhibited a rapid increase of productivity at this time, because diatoms have a storage vacuole and thereby nutrients such as P can be concentrated and used for cell division long after they are depleted in the bulk fluid. Elevated diatom biomass produced shading of light penetration, allowing for a low productivity for dinoflagellates. This study deepens our understanding of the impact of climate warming on lake systems and highlights the element biogeochemical cycle contributing to the variation of nutrients in the lake water column.

Comparison of bacterial growth in response to photodegraded terrestrial chromophoric dissolved organic matter in two lakes.

Terrestrial chromophoric dissolved organic matter (CDOM) could subsidize lake food webs. Trophic state and altitude have a pronounced influence on the CDOM concentration and composition of a lake. The impact of future changes in solar radiation on high-altitude lakes is particularly alarming because these aquatic ecosystems experience the most pronounced radiation variation worldwide. Photodegradation experiments were conducted on terrestrial CDOM samples from oligotrophic alpine Lake Tiancai and low-altitude eutrophic Lake Xiaohu to investigate the response of bacterial growth to photodegraded CDOM. During the photo-irradiation process, the fluorescent CDOM intensity evidently decreased in an inflowing stream of Lake Tiancai, with the predominance of humic-like fluorescence. By contrast, minimal changes were observed in the riverine CDOM of Lake Xiaohu, with the predominance of protein-like fluorescence. The kinetic constants of photodegradation indicated that the degradation rate of terrestrial (soil) humic acid in Lake Tiancai was significantly higher than that in Lake Xiaohu (p<0.001). Soil humic and fulvic acids irradiated in the simulated experiment were applied to incubated bacteria. The specific growth rate of bacteria incubated with soil humic substances was significantly higher in Lake Tiancai than in Lake Xiaohu (p<0.05). Furthermore, the utilizing rate of dissolved oxygen (DO) confirmed that the DO consumption by bacteria incubated with terrestrial CDOM in Lake Tiancai was significantly greater than that in Lake Xiaohu (p<0.05). In summary, the exposure of terrestrial CDOM to light significantly enhances its availability to heterotrophic bacteria in Lake Tiancai, an oligotrophic alpine lake, which is of importance in understanding bacterial growth in response to photodegraded terrestrial CDOM for different types of lakes.

Reusable electrochemical sensor for bisphenol A based on ionic liquid functionalized conducting polymer platform.

The toxicity of bisphenol A (BPA) has attracted considerable attention, and the reported electrochemical sensors for BPA need further improvement in reusability due to serious surface fouling. In this study, a composite film is designed aiming to provide both an accurate and repeatable platform for BPA determination. The conducting poly(3,4-ethylenedioxythiophene) film (PEDOT) and ionic liquid 1-butyl-3-methylimidazolium bromide (BMIMBr) were modified onto screen-printed carbon electrodes (SPCE) by electropolymerization and drop/spin methods, respectively. The surface characteristics of the composite film were characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and surface water contact angle experiments. The composite film-modified electrodes exhibited a linear response to BPA in the range of 0.1-500µM in pH 7.0 phosphate buffer solution (PBS) under optimized flow-injection amperometry. The method sensitivity and detection limit (S/N=3) were 0.2661µA µM(-1) (2.419µA µM(-1)cm(-2)) and 0.02µM, respectively. A relative standard deviation of 1.95% was obtained for 77 successive measurements of 10µM BPA, and the repeatability outperformed previously reported work. The proposed method was applied to detect BPA released from plastic water bottles using the standard addition method, and satisfactory recoveries were obtained. The electrochemical assay was validated by comparison with the chromatographic method, and the results showed good agreement between the two methods.

Sensitive and selective determination of gallic acid in green tea samples based on an electrochemical platform of poly(melamine) film.

In this work, an electrochemical sensor coupled with an effective flow-injection amperometry (FIA) system is developed, targeting the determination of gallic acid (GA) in a mild neutral condition, in contrast to the existing electrochemical methods. The sensor is based on a thin electroactive poly(melamine) film immobilized on a pre-anodized screen-printed carbon electrode (SPCE*/PME). The characteristics of the sensing surface are well-characterized by field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS) and surface water contact angle experiments. The proposed assay exhibits a wide linear response to GA in both pH 3 and pH 7.0 phosphate buffer solutions (PBS) under the optimized flow-injection amperometry. The detection limit (S/N = 3) is 0.076 µM and 0.21 µM in the pH 3 and pH 7 solutions, respectively. A relative standard deviation (RSD) of 3.9% is obtained for 57 successive measurements of 50 µM GA in pH 7 solutions. Interference studies indicate that some inorganic salts, catechol, caffeine and ascorbic acid do not interfere with the GA assay. The interference effects from some orthodiphenolic compounds are also investigated. The proposed method and a conventional Folin-Ciocalteu method are applied to detect GA in green tea samples using the standard addition method, and satisfactory spiked recoveries are obtained.

Comparison of optical properties of chromophoric dissolved organic matter (CDOM) in alpine lakes above or below the tree line: insights into sources of CDOM.

Here we investigated absorption and fluorescence properties of chromophoric dissolved organic matter (CDOM) in 15 alpine lakes located below or above the tree line to determine its source and composition. The results indicate that the concentrations of CDOM in below-tree-line lakes are significantly higher than in above-tree-line lakes, as evidenced from the absorption coefficients of a250 and a365. The intensities of the protein-like and humic-like fluorescence in below-tree-line lakes are higher than in above-tree-line lakes as well. Three fluorescent components were identified using parallel factor analysis (PARAFAC) modelling. Component 1 is probably associated with biological degradation of terrestrial humic component. The terrestrial humic-like component 2 is only found in below-tree-line lakes. The protein-like or phenolic component 3 is dominant in above-tree-line lakes, which is probably more derived from autochthonous origin. In this study, (1) higher a250/a365 and S275-295 values indicate smaller molecular weights of CDOM in above-tree-line lakes than in below-tree-line lakes, and smaller molecular weights at the surface than at 2.0 m depth; (2) SUVA254 and FI255 results provide evidence of lower percent aromaticity of CDOM in above-tree-line lakes; and (3) FI310 and FI370 suggest a strong allochthonous origin at the surface in below-tree-line lakes, and more contribution from autochthonous biological and aquatic bacterial origin in above-tree-line lakes.