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Identifying primary environmental drivers mediating the quantity and quality of sedimentary organic matter (OM) in climate‐sensitive alpine lakes is crucial to understanding the role of alpine lakes in greenhouse gas emissions and Earth's climate system. Here, we characterized various pools of OM of 20 alpine lakes across the Tibetan Plateau, including bulk OM, water‐soluble OM and alkaline‐extracted OM from surface sediments, and dissolved OM (DOM) from surface water. The total organic carbon (TOC) content in sediments was low (< 3%), and δ13C of TOC and C : N ratios indicated limited allochthonous carbon inputs. Sedimentary water‐soluble OM and alkaline‐extracted OM were both dominated by low‐molecular‐weight, low‐aromaticity compounds with low contributions of terrestrial humic substances, suggesting that sedimentary leachable OM was primarily regulated by in‐lake sources and processes. Redundancy analysis showed that water depth, water transparency, and total phosphorus concentration in water column explained ~ 50% variance of sedimentary bulk and leachable OM, substantiating the importance of autochthonous sources and primary productivity in regulating the quantity and quality of sedimentary OM. Compared with lake surface water DOM, water‐soluble OM and alkaline‐extracted OM from sediments had higher proportions of terrestrial humic‐like substances, suggesting preferential preservation of allochthonous materials in sediments. Our results are the first to demonstrate a clear link between physical attributes and sedimentary OM in Tibetan lakes. The associated relations predict that the amount of total OM and autochthonous carbon preserved in sediments would increase due to the lake enlargement under the scenarios of climate warming and precipitation enhancement, which may amplify greenhouse gas emissions from Tibetan lakes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Phosphorus (P) inactivation agents (PIAs) have been widely used in lakes for eutrophic management. However, the interactions of riverine suspended particulate matter (SPM) with PIAs have not been elucidated to the point of complete confidence in the success of PIA application to eutrophic lakes. In this study, a long-term field incubation experiment was carried out to investigate the effects of riverine SPM on sediment internal P management. Fluorescence excitation emission matrix coupled with parallel factor (EEM–PARAFAC) was used to characterize dissolved organic matter (DOM) derived from SPM/sediment, and to study its complexation with La (III) and Ca (II) contained in two PIAs. The analysis identified one protein-and two humic-like components in these samples, which show variable quenching effects by La (III) and Ca (II). The continuous settling of SPM can bury PIAs deeper into the sediment layers and while increasing the mobile P content in surface sediments. This consequently made an increase of P fluxes and surface sediment reactivity, which was witnessed by the increased labile P concentration measured by diffusive gradient in film (DGT). However, the binding capacity of PIAs towards sediment mobile P was kept in a buried layer during the six months’ field experiment. This study indicates that the influence mechanism of riverine SPM on PIAs was through a decrease of the reactive sorption sites of PIAs by complexing with DOM and continuously increasing the mobile P content in surface sediment thereby largely surpassing their maximum P sorption capacity. Repeated dosing at scheduled times would be better for turbid eutrophic lake remediation with high input of riverine SPM in long-term management. [ABSTRACT FROM AUTHOR]

Due to climate change, tree line advance is occurring in many alpine regions. Within the next 50 to 100 years, alpine lake catchments are expected to develop increased vegetation cover similar to that of sub-alpine lake catchments which currently exist below the tree line. Such changes in vegetation could trigger increased allochthonous DOM inputs to alpine lakes. To understand the fate of allochthonous DOM in alpine lakes impacted by climate change, the photochemical reactivity of DOM in sub-alpine Lake Tiancai (located 200 m below the tree line) was investigated by excitation emission matrix fluorescence combined with parallel factor analysis (EEM-PARAFAC) and UV–Vis spectra analysis. With photo-exposure, a decrease in apparent DOM molecular weight was observed and 32% DOM was photomineralized to CO 2 . Interestingly, the aromaticity of DOM increased after photodegradation, as evidenced by increases in both the specific UV absorbance at 254 nm (SUVA 254 ) and the humification index (HIX). Five EEM-PARAFAC components were identified, including four terrestrially-derived substances (C1, C2, C3 and C4; allochthonous) and one tryptophan-like substance (C5; autochthonous). Generally, allochthonous DOM represented by C2 and C3 exhibited greater photoreactivity than autochthonous DOM represented by C5. C4 was identified as a possible photoproduct with relatively high aromaticity and photorefractive tendencies and contributed to the observed increase in SUVA 254 and HIX. UV light facilitated the photodegradation of DOM and had the greatest effect on the removal of C3. This study provides information on the transformation of EEM-PARAFAC components in a sub-alpine lake, which is important in understanding the fate of increased allochthonous DOM inputs to alpine lakes impacted by climate change. [ABSTRACT FROM AUTHOR]

• In situ production and transformation of OM driven by algae blooms was studied • With sediments' supply, nutrients, metals and OM increased by 2–4 times in water • Particle OM (POM) was enriched in protein-like and low-molecular-weight component • Dissolved OM (DOM) showed higher %humic-like and high-molecular-weight component • Microbes played an efficient role in formation of potentially refractory DOM The generation of organic matter (OM) occurs synchronously with phytoplankton growth. Characterization of the generated particulate and dissolved OM during algal blooms in eutrophic lakes is crucial for better understanding the carbon cycle but remains limited. We speculate that sediments play a critical role in the biogeochemical transformation of OM derived from algal blooms in shallow lakes. In this study, changes in OM quantity and quality and the concentrations of biogenic elements (nutrients and metals) during algal blooms, were studied in situ in a shallow eutrophic lake (Lake Chaohu, China). Two enclosure treatments in the presence and absence of sediments were compared, and the cause-effect relationships among sediment, nutrients, metals, phytoplankton, particulate OM (POM), and dissolved OM (DOM) were revealed by a partial least square-path model (PLS-PM). The results showed that the changes in nutrients and metals concentrations over time were consistent with that of chlorophyll a (Chl a), and at the end of the treatment, the concentrations of Chl a , nutrients, and metals in Treatment S (with sediments) were approximately 3–5 times of those in Treatment N (without sediments). The high concentration of Chl a in Treatment S resulted in a high quantity of POM, which showed low molecular weight, low humification, and was enriched in protein-like components (∼ 70%). For DOM, the quantity increased after the decrease in POM, and DOM quality showed a significantly higher abundance of humic-like components and a higher molecular weight than POM did. The PLS-PM results showed that the significant positive effects of sediment on nutrients, metals, phytoplankton, POM, and DOM were 0.28, 0.37, 0.28, 0.25, and 0.25, respectively, suggesting that sediment had an important role in the biogeochemical cycles of these substances. The significant negative relationship between POM and DOM (-0.62) and the distinct difference in POM and DOM quality implied the efficient transformation of the freshly generated OM to those with a higher molecular weight, higher humification, and potentially refractory. Our results depicted the quick biogeochemical transformation of nutrients, metals, and the potential formation of refractory organic carbon in water column, as driven by the couple of the algae pump with the microbial carbon pump. Graphical Abstract [Display omitted]. [ABSTRACT FROM AUTHOR]

Highlights: [•] Photodegradation of GA, a simple model of DOM, was studied at various pH levels. [•] The direct photolysis rate of GA decreased with decreasing pH. [•] ROS can originate solely from DO or from the interaction between Fe3+ and DO. [•] A pH of 5 is most suitable for ROS formation and allowed rapid degradation of GA. [•] The contribution of ROS oxidation is greater than 71% at each pH value. [ABSTRACT FROM AUTHOR]

Highlights: [•] TaON exhibited higher photocatalytic activity than Ta3N5. [•] eCB is captured by either Fe3+ or H2O2 and hVB could not oxidize atrazine. [•] OH, from the reduction of H2O2 by Fe2+ or by eCB, is the active species. [•] By capturing eCB, H2O2 was preferred to be reduced to H2O than to OH. [•] TaON showed the higher separation efficiency of electrons and holes than Ta3N5. [ABSTRACT FROM AUTHOR]

Abstract: In order to overcome the limitation of the application of nanoparticles, tantalum (oxy)nitrides nanotube arrays on a Ta foil were synthesized and introduced in vis (visible light)-Fenton-like system to enhance the degradation of atrazine. At first, the anodization of tantalum foil in a mild electrolyte solution containing ethylene glycol and water (v:v=2:1) plus 0.5wt.% NH4F produced tantala nanotubes with an average diameter of 30nm and a length of approximately 1μm. Then the nitridation of tantala nanotube arrays resulted in the replacement of N atoms to O atoms to form tantalum (oxy)nitrides (TaON and Ta3N5), as testified by XRD and XPS analyses. The synthesized tantalum (oxy)nitrides nanotubes absorb well in the visible region up to 600nm. Under visible light, tantalum (oxy)nitrides nanotube arrays were catalytically active for Fe3+ reduction. With tantalum (oxy)nitrides nanotube arrays, the degradation of atrazine and the formation of the intermediates in vis/Fe3+/H2O2 system were significantly accelerated. This was explained by the higher concentration of Fe2+ and thus the faster decomposition of H2O2 with tantalum (oxy)nitrides nanotubes. In addition, tantalum (oxy)nitrides nanotubes exhibited stable performance during atrazine degradation for three runs. The good performance and stability of the tantalum (oxy)nitrides nanotubes film with the convenient separation, suggest that this film is a promising catalyst for vis-Fenton-like degradation. [Copyright &y& Elsevier]

Abstract: Tantalum (oxy)nitrides were prepared by the nitridation of Ta2O5 and were added to a photo-Fenton-like system to enhance Fe3+ reduction and atrazine degradation under visible light. The samples were characterized by XRD, XPS, DRS and BET analyses. XPS analysis showed that the nitrogen content of the tantalum (oxy)nitride samples increased noticeably with the nitridation temperature and nitridation time but slightly with the flow rate of NH3. XRD results showed Ta2O5 was first converted to TaON and then to Ta3N5 when the nitridation temperature increased. DRS analysis showed that the sample obtained at 800°C displayed the strongest absorption of visible light. However, the ability of the tantalum (oxy)nitrides to reduce Fe3+ did not increase continuously with the nitrogen content. Sample 7 (700°C, , 6h) showed the highest level of photocatalytic activity for Fe3+ reduction. This is because the photocatalytic activity of TaON for Fe3+ reduction is higher than that of Ta3N5. And a slight synergetic effect was observed between TaON and Ta3N5. With the addition of sample 7, H2O2 decomposition and atrazine degradation were significantly accelerated in a photo-Fenton-like system under visible light. The regenerated tantalum (oxy)nitrides catalyst displayed considerably stable performance for atrazine degradation. [Copyright &y& Elsevier]

Abstract: In this article, the photo-degradation of 4-chlorophenol (4-CP) under UV irradiation was studied with focus on the photodecomposition of 4-CP by reactive oxygen species (ROS). 4-CP underwent much faster and more complete degradation in UV/air system than in UV/N2 system. In UV/air system, the addition of t-butanol, a well-known •OH scavenger, significantly impeded the degradation of 4-CP. In the presence of t-butanol, the tendencies for the degradation of 4-CP and the formation of intermediates in UV/air system were very similar to those in UV/N2 system. In UV/air system, 4-CP was degraded by two pathways, direct photolysis by absorbing the photons and the oxidation via •OH. The contribution of direct photolysis and the oxidation via •OH to 4-CP decomposition were 17.2% and 82.8%, respectively based on the apparent kinetic constants. Hydrogen peroxide, which could produce •OH through photolysis, was formed in UV/air system. It was shown that dissolved oxygen, organic matter in excited state and hydrogen ion are all necessary for the formation of hydrogen peroxide. The formation mechanism of H2O2 was proposed based on experimental evidence. [Copyright &y& Elsevier]

Abstract: In this study, the role of oxygen in the regeneration of Fe(III) during the degradation of atrazine in UV/Fe(III) process was studied. The degradations of atrazine in UV/Fe(III) and UV-photolysis processes in the presence and absence of oxygen were compared. The results showed that the degradations of atrazine in these processes followed the pseudo-first-order kinetics well. The process exhibiting the highest rate constant (k) was UV/Fe(III)/air process, because k-value for UV/Fe(III)/air process was about 1.47, 2.23 and 2.56 times of those for UV/Fe(III)/N2, UV/air and UV/N2 processes, respectively. The degradation of atrazine was enhanced by oxygen in UV/Fe(III) process and the enhancement was more remarkable at higher initial concentrations of Fe(III). The investigation into the changes of Fe(III) concentrations demonstrated that the presence of oxygen led to the regeneration of Fe(III), which resulted in the enhancement of atrazine degradation. With air bubbling, the ferric ions were 25% more than those with N2 bubbling. The experimental data showed the regeneration of Fe(III) required the excited organic molecules and oxygen and on the basis of these results, the regeneration mechanism of Fe(III) was proposed. It was also found that due to the oxidation of Fe(II), the degradation of atrazine in UV/Fe(II)/air process was effective at a low Fe(II) concentration of 7mg/L, similar to that in UV/Fe(III)/air process. This study makes clear the role of oxygen in the regeneration of Fe(III), and thus it provides a guide to reduce the input of Fe(III) and is helpful to the application of UV/Fe(III) process in practice. [Copyright &y& Elsevier]

A kinetic model of the degradation of 4-CP by Fenton/O2 system was established, in which particular attention was paid to the role of oxygen in the process because many former researches suggested that the presence of oxygen could decrease the input of H2O2. The proposed model well predicted 4-CP degradation and H2O2 consumption by Fenton/O2 and Fenton/N2 systems at varying levels of Fe2+, H2O2, and 4-CP input. Most correlation coefficients between experimental and predicted data of 4-CP and H2O2 concentration were above 0.95. The model could predict the enhancement of 4-CP degradation by oxygen and the difference in the evolution of aromatic intermediates between Fenton/O2 and Fenton/N2 system. The predicted and experimental data both showed the degree of benzene ring cleavage in Fenton/O2 system was higher than that in Fenton/N2 system. Understanding the role of oxygen is very important to improve the decomposition performance. [Copyright &y& Elsevier]

Abstract: The role of oxygen in the degradation pathway of 4-CP by Fenton system was investigated in this paper. The degradation of 4-CP, changes of Fenton reagent''s concentration and formation of the intermediates in Fenton/O2 system were respectively compared with those in Fenton/N2 system. The result showed that both 4-CP degradation and CODcr removal in Fenton/O2 system were prior to those in Fenton/N2 system. Investigation into the intermediates suggested that the presence of oxygen impeded the formation of 4-chlorocatechol and accelerated the production of organic acids such as maleic acid, fumaric acid, acetic acid and oxalic acid. Based on the changes of reaction substances and the intermediates, the degradation mechanism of 4-CP by Fenton system in the presence of O2 was suggested. The dissolved oxygen competed against hydroxyl radical to react with ortho-parachlorohydroxyphenyl radical (ClHPng ortho-parachlorophenolperoxyl radical (ClPPeding the generation of 4-chlorocatechol. In addition, the reaction of oxygen with (Cl)PP radical increased the extent of benzene ring cleavage, producing more aliphatic organic acids. This study makes clear the mechanism of Fenton/O2 system and thus, it is helpful to establish the kinetic model and provide a good guide to the treatment of real wastewater. [Copyright &y& Elsevier]

Abstract: The degradation of three phenolic compounds, 4-chlorophenol, 4-nitrophenol and phenol by Fenton-like process was divided into three phases: the initiation phase, the fast phase and the termination phase. Compared with the initiation phase, the degradation of phenolic compounds, the consumption of H2O2 and the generation of Fe2+ accelerated dramatically in the fast phase. At the end of the fast phase, about 80% phenolic compounds were removed. After then, the degradation rate slowed down sharply due to the lack of H2O2. The enhancement in the fast phase was caused by the role of some hydroquinone-like intermediates such as hydroquinone, catechol and 4-chlorocatechol, which were identified to reduce Fe3+ to Fe2+ quickly. The fast degradation of phenolic compounds promoted the formation of intermediates, thus the concentration of Fe2+ increased, and vice versa. A reaction pathway describing the role of the hydroquinone-like intermediates was suggested. [Copyright &y& Elsevier]

Human activities can alter dissolved organic matter (DOM) in lakes through both direct (i.e., exporting DOM of anthropogenic sources) and indirect effects (i.e., enhancing the autochthonous production of DOM via nutrient loading). Distinguishing between the direct and indirect effects is important to better understand human impacts on aquatic systems, but it remains highly challenging due to the interdependence of associated environmental variables. Here, we demonstrated that disentangling the direct and indirect effects can be achieved through combining large-scale environmental monitoring with the Partial Least Squares Path Modeling (PLS-PM). We presented DOM data from 61 lakes within the floodplain of the Yangtze River (Lakes-YR), China, a region that has been subjected to intense anthropogenic disturbances. We analyzed the amount and composition of DOM through dissolved organic carbon (DOC), chromophoric DOM (CDOM), and fluorescent DOM (FDOM). Four fluorescence components were identified, including one tyrosine-like component, one tryptophan-like component, and two humic-like components. Most of the lakes were dominated by freshly produced DOM with small molecular weights and low humification. Results from the PLS-PM models showed that the autochthonous production was more important than anthropogenic inputs in mediating DOC and CDOM. In contrast, FDOM parameters in lakes were more sensitive to the direct, anthropogenic sources, including treated domestic, industrial wastewater, and the effluents of aquaculture. These sources can be identified by elevated FDOM content per DOC (FDOM: DOC ratio) relative to autochthonous DOM, suggesting the potential of using FDOM as a tracer to identify and monitor the contribution of anthropogenic organic matter to inland waters. Unlabelled Image • Human activity can alter DOM in lakes directly and indirectly. • Direct and indirect effects are disentangled by path analysis modeling. • DOC and CDOM are more sensitive to nutrient loading and autochthonous DOM production. • FDOM parameters are more sensitive to direct DOM inputs from anthropogenic sources. • FDOM: DOC ratio may serve as a tracer for anthropogenic sourced DOM. [ABSTRACT FROM AUTHOR]

• Algal DOM (ADOM) showed stronger adsorption on FeOx than humic acid (HA). • ADOM had a stronger inhibition on phosphate sink than HA, promoting eutrophication. • Carboxylic-rich alicyclic molecules in ADOM contributed to strong adsorption. • Adsorption reduced source-specific compounds: aromatics in HA and proteins in ADOM. Dissolved organic matter (DOM) is a heterogeneous pool of compounds and exhibits diverse adsorption characteristics with or without phosphorous (P) competition. The impacts of these factors on the burial and mobilization of organic carbon and P in aquatic ecosystems remain uncertain. In this study, an algae-derived DOM (ADOM) and a commercially available humic acid (HA) with distinct compositions were assessed for their adsorption behaviors onto iron (oxy)hydroxides (FeO x), both in the absence and presence of phosphate. ADOM contained less aromatics but more protein-like and highly unsaturated structures with oxygen compounds (HUSO) than HA. The adsorption capacity of FeOx was significantly greater for ADOM than for HA. Protein-like and HUSO compounds in ADOM and humic-like compounds and macromolecular aromatics in HA were preferentially adsorbed by FeOx. Moreover, ADOM demonstrated a stronger inhibitory effect on phosphate adsorption than HA. This observation suggests that the substantial release of autochthonous ADOM by algae could elevate internal P loading and pose challenges for the restoration of restore eutrophic lakes. The presence of phosphate suppressed the adsorption of protein-like compounds in ADOM onto FeOx, resulting in an increase in the relative abundance of protein-like compounds and a decrease in the relative abundance of humic-like compounds in post-adsorption ADOM. In contrast, phosphate exhibited no discernible impact on the compositional fractionation of HA. Collectively, our results show the source-composition characters of DOM influence the immobilization of both DOM and P in aquatic ecosystems through adsorption processes. The preferential adsorption of proteinaceous compounds within ADOM and aromatics within HA highlights the potential for the attachment with FeO x to diminish the original source-specific signatures of DOM, thereby contributing to the shared DOM characteristics observed across diverse aquatic environments. This is special type of abstract that is so short and could be inserted after main abstract of article, as a blurb or inserted as annotations into a Table of contents [Display omitted] [ABSTRACT FROM AUTHOR]

Dissolved organic matter (DOM) plays important roles in the aquatic biogeochemical cycle and the global carbon cycle. However, it is highly spatially and temporally varied due to complex sources from the catchment (allochthonous) and from within the system (autochthonous). Satellite remote sensing provides the ability to monitor DOM and identify the spatio-temporal variations in lakes on a global or regional scale. In this study, field work was conducted in 55 lakes in August 2012 along the middle and lower reaches of the Yangtze River (MLR-YR), where most lakes were characterized by eutrophication due to intense human activities. The results showed that both colored DOM (CDOM) and total DOM differed significantly by and were linearly related to the human-induced trophic state index (TSI), with R 2 = 0.41 and 0.61, respectively. Autochthonous substances by phytoplankton contributed to 38.5% of CDOM and 35.2% of DOM, and allochthonous terrestrial substance indexed by land cover change and aquaculture contributed to almost half, with 49.7% of CDOM and 49.8% of DOM. In total, human activities explained as much as 81.7% and 87.5% of the variations in CDOM and DOM, respectively. Finally, a flowchart for estimating DOM from satellite-derived TSI was proposed. This study has great significance for synchronously monitoring and managing aquatic environment quality in regional eutrophic lakes around the world. Image 1 • Quantity and composition of DOM were greatly varied in lakes along the Yangtze River. • Human activities explained 81.7% and 87.5% variations in CDOM and DOM, respectively. • Trophic state index could serve as a bridge for remotely monitoring DOM from Chl-a. [ABSTRACT FROM AUTHOR]

This paper reported the degradation of 4-CP wastewater by a novel photocatalysis oxidation system—UV/Fe2+/air system, in which air was used as a cheap oxidant that reacted with the excitation state of organics to form H2O2 under the UV light. The formed H2O2 reacted with the added ferrous ion to form Fenton reaction and led to the quick degradation of organic pollutants. It was found that 4-CP could be completely removed within 40 min. The degradation of 4-CP in the UV/Fe2+/air system was superior to the conventional UV/Fenton system (the initial concentration of H2O2 was 22 mg·L-1). UV/Fe2+/air is an effective and cheap method for treatment of the organics that can be excited by UV light. [ABSTRACT FROM AUTHOR]

Dissimilatory iron reduction (DIR) can drive the release of organic carbon (OC) as carbon dioxide (CO2) by mediating electron transfer between organic compounds and microbes. However, DIR is also crucial for carbon sequestration, which can affect inorganic‐carbon redistribution via iron abiotic–phase transformation. The formation conditions of modern carbonate‐bearing iron minerals (ICFe) and their potential as a CO2 sink are still unclear. A natural environment with modern ICFe, such as karst lake sediment, could be a good analog to explore the regulation of microbial iron reduction and sequential mineral formation. We find that high porosity is conducive to electron transport and dissimilatory iron‐reducing bacteria activity, which can increase the iron reduction rate. The iron‐rich environment with high calcium and OC can form a large sediment pore structure to support rapid DIR, which is conducive to the formation and growth of ICFe. Our results further demonstrate that the minimum DIR threshold suitable for ICFe formation is 6.65 μmol g−1 dw day−1. DIR is the dominant pathway (average 66.93%) of organic anaerobic mineralization, and the abiotic‐phase transformation of Fe2+ reduces CO2 emissions by ~41.79%. Our findings indicate that as part of the carbon cycle, DIR not only drives mineralization reactions but also traps carbon, increasing the stability of carbon sinks. Considering the wide geographic distribution of DIR and ICFe, our findings suggest that the "iron mesh" effect may become an increasingly important vector of carbon sequestration. [ABSTRACT FROM AUTHOR]

Human land use has led to significant changes in the character of dissolved organic matter (DOM) in lotic ecosystems. These changes are expected to have important environmental and ecological consequences. However, high spatiotemporal variability has been reported in previous studies, and the underlying mechanisms remain inadequately understood. This study assessed variation in the properties of stream water DOM within watersheds across a gradient of agricultural land use with grazing pasture lands as the dominant agricultural type in the southeastern United States. We collected water samples under baseflow conditions five times over eight months from a regional group of first- to fourth-order streams. Samples were analyzed for dissolved organic carbon (DOC) concentration, DOM quality based on absorbance and fluorescence properties, as well as DOM biodegradability. We found that air temperature and antecedent hydrological conditions (indicated by antecedent precipitation index and stream water sodium concentrations) positively influenced stream water DOC concentration, DOM fluorescence index, and the proportion of soil-derived, microbial humic fluorescence. This observation suggests that elevated production and release of microbial DOM in soils facilitated by high temperature, in conjunction with strong soil-stream hydrological connectivity, were important drivers for changes in the concentration and composition of stream water DOM. By comparison, watersheds with a high percentage of agricultural land use showed higher DOC concentration, larger proportion of soil-derived, humic-like DOM compounds, and higher DOC biodegradability. These observations reflect preferential mobilization of humic DOM compounds from shallow organic matter-rich soils in agricultural watersheds, likely due to enhanced soil erosion, organic matter oxidation and relatively shallow soil-to-stream flow paths. [ABSTRACT FROM AUTHOR]

Highlights: [•] TiO2 nanotubes showed high photocatalytic activity for microcystin-LR degradation. [•] Conjugated system and methoxy group in Adda chain are liable to be attacked by OH. [•] Conjugated system in Mdha amino acid is susceptible to be attacked by OH. [•] Carboxyl and amino groups of the peptides are inferred to be hydrolyzed. [•] Adda is proposed to be separated from heptapeptides, leaving alkyl derivatives. [Copyright &y& Elsevier]

In order to obtain TiO2 with high photocatalytic activity, a cathode reduction was used to dope I7+ and I5+ into TiO2 nanotubes of anodized Ti in C2H2O4⋅2H2O + NH4F electrolyte. SEM images show that the anodization method integrated the preparation with the doping process, which for nonmetals-doping is advantageous to maintain the morphological integrity of TiO2 nanotubes. I7-I5+-doping enhances the UV response of TiO2 and result in a red-shift. Under UV/visible irradiation, a I7+-I5+-doped sample (400°C) showed the highest Iph and photocatalytic efficiency. A part of I- in the I7+-I5+-doped sample is involved in the UV response, the red-shift and the higher Iph. [ABSTRACT FROM AUTHOR]

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, αβ-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. • Lipid biomarkers and trace elements in sediment core were used to reflect lake pollution. • Geochemical variables remained low in sediments prior to 1970s, reflecting an unpolluted state. • Pollution of the lake in ca. 1970–1990 was driven by use of chemical fertilizers, pesticides and diesel oil. • Direct application of chemical fertilizers in aquaculture resulted in a massive pollution. [ABSTRACT FROM AUTHOR]

Highlights • Fatty acids and alcohols were analyzed in surface sediments of lakes in Eastern China. • Abundances of fatty acids were dependent on the type of organisms within the lakes. • Variation of trophic status in lakes exerted influence on some alcohols in sediments. • (C26 + C28)/(C22 + C24) n -alkanoic acids or n -alkanols can indicate transition of lake ecosystems. Abstract During the past hundred years, the majority of lakes along the middle and lower reaches of the Yangtze River (MLRYZ) have been greatly impacted by human intervention, resulting in a significant spatial heterogeneity in water and ecosystem quality. We quantified the fatty acid (FA), n -alkanol, sterol and long-chain alkyl diol content of surface sediments of MLRYZ lakes in order to determine how ecological differences (algae versus macrophyte-dominated state) and trophic status influence the composition, origin and abundance of lipid biomarkers in the sediments. Based on the results, variation in FAs appears to be mainly controlled by the type of organisms within the lakes. Short-chain n -alkanoic acids, monounsaturated FAs (MUFAs) and polyunsaturated FAs (PUFAs) were generally more abundant in sediments of algal lakes (lacking macrophyte growth) than in lakes with macrophyte growth. The opposite trend was apparent for long-chain n -alkanoic acids. Ratios of (C26 + C28)/(C22 + C24) n -alkanoic acids differed significantly between macrophyte and algal lakes. In the alcohol fraction, lipid biomarker abundance appeared to be controlled by trophic status of the lake, with the exception of cholesterol and long-chain n -alkanols whose abundances were closely related to the present organisms and exhibiting greater abundances in algal lakes. Enhanced levels of total phosphorus (TP) and total nitrogen (TN) in a lake create greater concentrations of C32 1,15 alkyl diol and brassicasterol respectively, while the abundance of dinosterol and the ratio of dinosterol/brassicasterol decline in line with increase in TP and TN, respectively. Ratios of (C26 + C28)/(C22 + C24) n -alkanol were also greatly influenced by the type of organisms present, exhibiting higher values in algal lakes. The sensitivity of these sediment lipid biomarker responses points to a potentially useful role as proxies for biological community types and trophic status in paleolimnology studies. [ABSTRACT FROM AUTHOR]

Alpine lake habitats are evolving into subalpine lakes under the scenario of climate change, where the vegetation are promoted due to increasing temperature and precipitation. The abundant terrestrial dissolved organic matter (TDOM) leached from watershed soil into subalpine lakes would undergo strong photochemical reaction due to the high altitude, with the potential to alter DOM composition and affect the bacterial communities. To reveal the transformation of TDOM by both photochemical and microbial processes in a typical subalpine lake, Lake Tiancai (located 200 m below the tree line) was chosen. TDOM was extracted from the surrounding soil of Lake Tiancai and then subjected to the photo/micro-processing for 107 days. The transformation of TDOM was analyzed by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and fluorescence spectroscopy, and the shift of bacterial communities was analyzed using 16s rRNA gene sequencing technology. Dissolved organic carbon and light-absorbing components (a 350) decay accounted for approximately 40% and 80% of the original, respectively, in the sunlight process, but both less than 20% in the microbial process for 107 days. The photochemical process promoted the chemodiversity as there were ∼7000 molecules after sunlight irradiation, compared to ∼3000 molecules in the original TDOM. Light promoted the production of highly unsaturated molecules and aliphatics, which were significantly associated with Bacteroidota , suggesting that light may influence bacterial communities by regulating the DOM molecules. Carboxylic-rich alicyclic molecules were generated in both photochemical and biological processes, suggesting TDOM was converted to a stable pool over time. Our finding on the transformation of terrestrial DOM and the alternation of bacterial community under the simultaneously photochemical and microbial processes will help to reveal the response of the carbon cycle and lake system structure to climate change for high-altitude lakes. [Display omitted] • Photo-/bio-transformation of terrestrial DOM for a subalpine lake was studied. • Sunlight irradiation promoted DOM chemodiversity compared to the microbial process. • Bioavailable molecules were photo-produced, which altered the microbial community. • Refractory carboxylic-rich alicyclic molecules increased after photo/bio-process. [ABSTRACT FROM AUTHOR]

The stability of organic matter-iron-phosphate (OM-Fe-P) association has an important impact on the migration and sequestration of organic carbon (OC) and P in the environment. Here, we examined the release characteristics of Fe, P and OM due to the abiotic reduction of OM-Fe-P associations by Na-dithionite. The associations were synthesized with algae-derived OM (AOM) and terrestrial humic acid (HA) through either adsorption onto iron (hydr)oxide or coprecipitation with Fe(III). Results indicated that OM and P adsorbed onto the associations were rapidly released, whereas coprecipitation yielded much lower release rates of Fe, P, and OM. The stronger inhibitory effect on reduction from coprecipitation can be explained by larger particles formed by coprecipitation and coprecipitation taking up more OC that had a passivation effect on the associations. The release rates of OM and P were lower in coprecipitates formed with HA than formed with AOM for a given OC/Fe ratio. This observation can be attributed to a patchy distribution of OC in AOM associated coprecipitates, which showed a weaker aggregation of OC with Fe and P. In contrast, the distribution of OC in HA-associated coprecipitates was more homogenous, enabling a stronger aggregation of OM with P and a greater passivation effect on P release. Our results revealed that OM sources, association formation pathways, and elemental stoichiometry collectively controlled the stability of OM-Fe-P associations. [Display omitted] • Organic matter-iron-phosphate association (OM-Fe-P) was chemically reduced. • OM-Fe-P formed via coprecipitation was reduced slower than that via adsorption. • Composition and distribution of OM determines immobilization of OC. • Terrestrial humic acid facilitated OM-Fe-P coprecipitates' stability better than algal OM. [ABSTRACT FROM AUTHOR]

The biogeochemical cycles of phosphorus (P) and organic matter (OM) are significantly influenced by iron (Fe) through forming OM-Fe-P associations. The sources and compositions of organic matter in the two typical states (algae-dominated and macrophyte-dominated) of shallow lakes are different, which could modulate the formation of OM-Fe-P associations and influence the internal loadings of P in lakes. In this study, OM and P bound with Fe were extracted from the sediments of algae-dominated zone (A-zone) and macrophyte-dominated zone (M-zone) in Lake Taihu via the citrate-bicarbonate-dithionite (CBD) reduction method, and were analyzed to elucidate the differences in OM-Fe-P associations between the two zones. The results showed that OM-Fe-P associations in the sediments of M-zone had higher a molar C/Fe ratio but a lower molar P/Fe ratio. Four components identified by excitation-emission matrix fluorescence coupled with parallel factor analysis (EEM-PARAFAC) in OM-Fe-P associations in the two zones were all humic-like substances and the relative abundance of the corresponding PARAFAC components had no significant difference between the two zones. However, the total fluorescence intensity of the humic-like components was higher in M-zone than those in A-zone. This could be attributed to the higher aromaticity of OM produced from macrophyte than that from algae, as evidenced by the difference in the easily-desorbed OM between two zones. In M-zone, high aromatic compounds which are preferentially associated with Fe, could be more produced from macrophyte plants than from algae and resulted in the higher C/Fe molar ratio. The higher C/Fe molar ratio (2.1 ± 0.9) of OM-Fe-P associations in M-zone reflected that more OM originated from macrophyte could be involved in the coprecipitation with Fe (III) and OM-Fe-P associations in M-zone were probably more resistant to the microbial and chemical reduction. Our results from the real situation confirmed the mechanism related to the role of OM composition in the reduction of OM-Fe-P associations to explain the lower internal loading of P in M-zone than that in A-zone. [ABSTRACT FROM AUTHOR]

Black blooms have been associated with fish-kills and the loss of benthic fauna as well as closure of potable water supplies. Their frequency and duration has increased in recent decades in rivers, inland lakes and reservoirs, and has often been associated with the decay and release of organic matter (planktonic algae, aquatic macrophytes, sediment release, etc.). However, the interactions between microbial, chemical, hydrodynamic and optical conditions necessary for black blooms are poorly understood. The present study combines field investigations and laboratory mesocosm studies to show that black blooms are caused by a combination of high CDOM (chromophoric dissolved organic matter) absorption, the formation of CDOM-Fe complexes and low backscattering. Mesocosm experiments showed that black bloom conditions occur after 4 days, with a significant increase in the concentrations of Fe 2+ and ∑S 2− . Total absorption (excluding absorption due to water) at 440 nm increased by 30% over this time to 7.3 m −1 . In addition, the relative contribution of CDOM absorption to the non-water total absorption increased from 18% to 50%. Regression analyses between chemical and bio-optical data in both field and mesocosm experiments indicated that the concentrations of Fe 2+ co-varied positively with CDOM absorption a g (440) (R 2 > 0.70), and the specific CDOM absorption (a g (440)/DOC). Conditions that favored the development of black blooms were elevated algal or macrophyte biomass and limited water column mixing. [ABSTRACT FROM AUTHOR]

Humic acid (HA) and phosphate interactions play a vital role in the biogeochemical cycle of carbon and nutrients and thus the trophic state of a lake. The adsorption behavior of HAs to sediments in the absence and presence of phosphate was investigated in this study. Three types of HAs were used, AHA from algae-dominated lake sediments, MHA from macrophyte-dominated lake sediments, and a reference HA (RHA) with terrestrial sources. The adsorption capacity of lake sediments was highest for AHA, which can be explained by that AHA contained more carboxyl-containing molecules, proteinaceous compounds and polysaccharides that were preferentially adsorbed by minerals. Phosphate showed a stronger inhibitory effect on MHA adsorption than on AHA adsorption, suggesting that AHA can more effectively replace phosphate adsorbed to sediments. Our findings show that the functional groups of organic compounds control not only their fractionation and burial but also their ability to replace phosphate in sediments. We propose a novel mechanism to explain the legacy effect of lake eutrophication. That is, as lakes shift from a macrophyte-dominated state to more eutrophic, algae-dominated state, increasing algae-derived organic compounds can promote the release of phosphate from sediments, forming a positive feedback loop that sustains internal phosphorus loading and hence lake eutrophication. [Display omitted] • Sole and competitive adsorption with phosphate of humic acids (HA) of three sources were studied. • Adsorption capacity of sediments was highest for HA from algae-dominated lake. • Carboxyl-containing molecules, proteins and polysaccharides were preferentially adsorbed. • Inhibition extent of phosphate on HA adsorption was closely related to HA composition. • Algae-derived organics can promote P mobilization from sediments and enhance internal P loading. [ABSTRACT FROM AUTHOR]

The coprecipitation of dissolved organic matter (DOM) and phosphate with Fe(III) at the sediment-water interface plays an important role in the biogeochemical cycle of organic carbon (OC) and phosphorus (P) in aquatic ecosystems. However, studies remain limited towards understanding the strength of ternary DOM-phosphate-Fe(III) coprecipitation in sequestering OC and P. Here, we investigated the behaviors of humic acid (HA) and phosphate during their coprecipitation with Fe(III) and compared the coprecipitation behaviors with those during the adsorption process. The results showed that the coprecipitation of HA and phosphate with Fe(III) enhanced as pH decreased or initial Fe(III) concentrations increased. The presence of phosphate had a moderate inhibition effect on HA coprecipitation, leading to 3%–37% of reduction in precipitated HA. Changes in optical properties of DOM (i.e., SUVA 254 , E 2 /E 3 , and fluorescent components) showed that macromolecular, aromatic molecules preferentially coprecipitated, and this selectivity pattern was not influenced by the presence of phosphate. Compared to the adsorption of HA and phosphate to goethite, coprecipitation with Fe(III) displayed stronger binding ability, sequestering more than10 times of HA and phosphate, and was more efficient in sequestering protein-like compounds. The inhibitory effect of phosphate on HA sequestration was weaker during coprecipitation than during adsorption. Moreover, coprecipitation led to a lower degree of compositional fractionation of HA than adsorption, which may be explained by that inclusion, an important pathway for coprecipitation, has low selectivity for chemical compositions. Collectively, our results demonstrate that coprecipitation plays a crucial role in sequestering both OC and P in aquatic systems, arguing that the formation of ternary OC-Fe-P coprecipitates may be an important pathway for sequestering OC and P over a long term and reducing the internal loading of P in eutrophic lakes. [ABSTRACT FROM AUTHOR]

In order to investigate the catalytic performance of anodic TiO nanotubes and their practical application in the treatment of refractory microcystins (MCs) in natural-water samples, TiO nanotubes of diameter of 50-80 nm were fabricated by anodization in CHO·2HO containing NHF. Under irradiation with natural sunlight, MC-LR was totally degraded after 1 d using the anodic TiO nanotubes. In contrast, the removal efficiency without TiO nanotubes was as low as 47.7% within 20 d. In addition, a mixture of anatase and rutile TiO gave higher photocatalytic activity than the single phase did. The pH also influenced the adsorption capacity of the TiO nanotubes. The order of MC-LR degradation efficiencies at different pH values was 3.5 > 8.0 > 10.0. After five repeated experiments on the degradation of MC-LR for 7 h, the degradation efficiency was still stable. [ABSTRACT FROM AUTHOR]

Abstract: Fe–N-codoped TiO2 powder prepared by sol–gel method is loaded on low-density polyethylene film to obtain immobilized photocatalyst. The obvious agglomeration phenomena exist in the annealed samples with nanometer size, as observed in SEM images. XRD results suggest that the adding amount of impurities has a great effect on the crystallinity and particle size of TiO2. Compared with undoped and Fe/N-doped TiO2, Fe–N-codoped TiO2 shows an obviously higher catalytic activity under visible irradiation. The DFT calculations indicate that the doping of nitrogen and Fe induced the formation of new states between the valence band and conduction band. The codoping of TiO2 with nitrogen and Fe leads to the much narrowing of the band gap and greatly improves the photocatalytic activity under visible irradiation. Moreover, the Fe–N-codoping can promote the separation of the photogenerated electrons and holes to accelerate the transmission of photocurrent carrier. [Copyright &y& Elsevier]

Abstract: The increasing atmospheric CO2 level causes global warming and may pose catastrophic effects to the humanity. Among the various options to reduce the CO2 atmospheric loading, hydrothermal reactions may have a high potential for rapidly and effectively converting CO2 into useful chemicals. In this study, the hydrothermal conversion of CO2 into formic acid was carried out by using Fe as a reductant and Ni as a catalyst. The effect of various experimental parameters, e.g., amount of Fe (Ni), Fe/Ni ratio, temperature, reaction time, alkalinity etc. was investigated. Results showed that Ni played a catalytic role in the hydrothermal conversion of CO2 into formic acid. The highest yield of formic acid of 15.6% was achieved under optimal conditions, i.e., Fe/Ni ratio of 1:1, temperature of 300°C, reaction time of 120min, filling rate of 35% and NaHCO3: Fe of 1:6. Additionally, the selectivity of formic acid was more than 98%. It was also found that the hydrothermal conversion could not occur without either the addition of catalyst or the existence of CO2 when Fe was used as a reductant. The role of CO2 in the hydrogen production was discussed. [Copyright &y& Elsevier]

• We found that zooplankton were significant contributors of sediment FAs. • C18:1 ω9 and short-chain n -alkanoic acids might be largely derived from zooplankton. • Zooplankton might be significant contributors of middle-chain n -alkanoic acids in some lakes. • Input of zooplankton FAs was greatly reduced due to the development of aquaculture. • Contribution of algal and bacterial FAs increased with lake eutrophication and aquaculture. During the past few decades, the majority of shallow lakes in the Yangtze River basin (Eastern China) have been impacted by heavy discharges of sewage and the intensification of aquaculture. These activities have significant potential to alter aquatic ecosystems and these changes may be reflected in the composition of lipid biomarkers in sediments at the time. In order to evaluate this effect, the abundances and distribution of fatty acids (FAs) were measured in 210Pb dated sediment cores from two anthropogenically impacted shallow lakes in the Yangtze River basin, Changdang and Taibai. Results from Lake Changdang revealed an extreme enrichment of zooplankton-derived C22:1 ω11 in sediments, with C22:1 ω11/ n -C16 ratios reaching ~1.6 on average. This unusual distribution may have been caused by zooplankton blooms in the lake in the years before aquaculture was developed. Elevated abundances of C18:1 ω9 and short-chain n -alkanoic acids observed in pre-1977 sediments might be also derived from zooplankton. After 1977, FAs of zooplankton origin in Lake Changdang greatly declined in abundance, coincident with the introduction of planktivorous fish. Meanwhile, inputs of FAs from submerged/floating macrophytes, bacteria and algae increased as a result of eutrophication and reduced grazing pressure from zooplankton. In Lake Taibai, abundances of C22:1 ω11 were greatly reduced in all sediments and accounted for 38% of n -C16 on average, reflecting comparatively smaller inputs of zooplankton FAs owing to the earlier establishment of aquaculture in the lake. Relative enrichment of polyunsaturated FAs (PUFAs) and branched FAs (Br-FAs) in the sediments was attributed to high inputs of algal and bacterial organic matter (OM) in response to reduced predation and grazing by zooplankton. Rapid increases in PUFAs and Br-FAs in post-1970 sediments were driven by eutrophication in this period. [ABSTRACT FROM AUTHOR]

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 (R HO ∙) (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 R HO ∙ 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 R HO ∙ 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. Image 1 • Abundance, source, and influencing factors of R HO ∙ and [HO∙] in contrasting waters were studied. • River waters contained generally lower R HO ∙ and [HO∙] than the lake waters. • Nitrite and nitrate contributed 0.2–24.8% and 0.1–8.8% of HO∙ formation, respectively. • DOM photosensitization contributed more than 70% of HO∙ formation for all samples except for one river water. • Both abundance and inherent properties (SUVA 254 , HIX, and molecular weight) of DOM influenced [HO∙]. [ABSTRACT FROM AUTHOR]

• Profiles of n -alkanes in sediments were dependent on water column structure, nutrient inputs and catchment disturbance. • In deep lakes, non-photosynthetic bacterial and aquatic macrophytes were major contributors of n -alkanes. • Terrestrial plant sourced n -alkanes were exceptionally abundant in alpine lakes. • Eutrophication driven enrichment of short-chain odd carbon n -alkanes was recorded in shallow lakes. In paleolimnology studies, the trajectories of n -alkane abundances and distributions in dated sediments are widely used indicators of changing environmental and ecological status in the overlying water over time. However, the factors contributing to the variable n -alkane profiles of lake systems are not yet fully understood. Here, a comparative study was conducted to examine natural and anthropogenic influences on the sediment n -alkane profiles of five representative lakes in China. Core samples from the deep oligo- mesotrophic lakes Fuxian and Lugu (FX-1 and LG-1 cores), the shallow eutrophic lakes Taibai and Changdang (TB-1 and CD-1 cores) and the alpine Lake Heihai (HH-1 core) were used. While there were striking differences in n -alkane abundances and distributions between the cores, the results suggested that the n -alkanes in all five studied lakes were derived mainly from biogenic sources, rather than from petroleum contamination. The short-chain (C 21 n -alkane profiles of different cores varied significantly. Abundances of long-chain n -alkanes (C 29 , C 31 and C 33) in HH-1 were approximately 3–7 times greater than in other cores. Coupled with the lowest Paq (average 0.29) values recorded in the study, this indicates a predominantly terrestrial plant origin for the >C 21 n -alkanes, most likely the dense alpine meadow which surrounds the lake. In other cores, however, aquatic macrophytes appear to be more important contributors of the n -alkanes, a result that corresponds with the relatively low density of terrestrial plants in those catchments. [ABSTRACT FROM AUTHOR]