Application of various molecular markers for investigating petrogenic inputs in coastal systems strongly impacted by anthropogenic stressors.

In this study, multiple molecular markers [polycyclic aromatic hydrocarbons (PAHs), linear and branched alkanes, unresolved complex mixture (UCM), hopanes, and steranes] were applied to explore petroleum-related inputs in complex coastal systems influenced by various human-induced pressures. To investigate anthropogenic impacts related to petrogenic emissions, we analysed surface sediments from coastal areas of southern Baltic, including harbour/shipyard channels, offshore dumping sites, shipping routes, and major sinks for particulate matter discharged by large rivers. This study indicates a large spatial variability in the contamination degree of examined sites by petroleum-derived chemicals. Hopanes and steranes along with UCM appeared to have the highest potential to identify petroleum sources in studied locations, whereas investigations based on alkanes and PAHs seemed to be considerably affected by inputs of modern biogenic and combustion-derived materials, respectively. However, the combined use of all these markers provides deeper insight into the complexity of sedimentary organic matter in human-impacted environments.

Effects of dissolved oxygen changes in the benthic environment on phosphorus flux at the sediment-water interface in a coastal brackish lake.

In semi-enclosed coastal brackish lakes, changes in dissolved oxygen in the bottom layer due to salinity stratification can affect the flux of phosphorus (P) at the sediment-water interface, resulting in short- and long-term water quality fluctuations in the water column. In this study, the physicochemical properties of the water layers and sediments at five sites in Saemangeum Lake were analyzed in spring and autumn for four years, and phosphorus release experiments from sediments were conducted for 20 days under oxic and anoxic conditions during the same period. Sediment total phosphorus (T-P) decreased in autumn compared to spring due to mineralization of organic bound phosphorus, which was the most dominant P fraction. This may be related to the increase in the ratio of PO4-P to T-P in bottom waters in autumn, when hypoxia was frequently observed. The difference in P fluxes between oxic and anoxic conditions indicated that during autumn, as compared to spring, the release of phosphorus could have a more immediate impact on the water column during the formation of hypoxia/anoxia. The main factors influencing changes in P fluxes from sediments were identified through redundancy analysis. Additionally, based on the results of multiple regression analysis, sediment TOC, sediment non-apatite phosphorus, porewater pH, and porewater PO4-P were determined to be the most significant factors affecting P fluxes from sediments, depending on the season or redox conditions. Recently, the increased influx of seawater into Saemangeum Lake has been shown to contribute to water quality improvements in the water column due to a strong dilution effect. However, the sediment environment has shifted towards a more reduced state, leading to increased P release under anoxic conditions. Therefore, for future water quality management within the lake, it is necessary to consistently address the recurring hypoxia and continuously monitor phosphorus dynamics.

Multi-Technique Characterization of 3.45 Ga Microfossils on Earth: A Key Approach to Detect Possible Traces of Life in Returned Samples from Mars.

The NASA Mars 2020 Perseverance rover is actively exploring Jezero crater to conduct analyses on igneous and sedimentary rock targets from outcrops located on the crater floor (Máaz and Séítah formations) and from the delta deposits, respectively. The rock samples collected during this mission will be recovered during the Mars Sample Return mission, which plans to bring samples back to Earth in the 2030s to conduct in-depth studies using sophisticated laboratory instrumentation. Some of these samples may contain traces of ancient martian life that may be particularly difficult to detect and characterize because of their morphological simplicity and subtle biogeochemical expressions. Using the volcanic sediments of the 3.45 Ga Kitty's Gap Chert (Pilbara, Australia), containing putative early life forms (chemolithotrophs) and considered as astrobiological analogues for potential early Mars organisms, we document the steps required to demonstrate the syngenicity and biogenicity of such biosignatures using multiple complementary analytical techniques to provide information at different scales of observation. These include sedimentological, petrological, mineralogical, and geochemical analyses to demonstrate macro- to microscale habitability. New approaches, some unavailable at the time of the original description of these features, are used to verify the syngenicity and biogenicity of the purported fossil chemolithotrophs. The combination of elemental (proton-induced X-ray emission spectrometry) and molecular (deep-ultraviolet and Fourier transform infrared) analyses of rock slabs, thin sections, and focused ion beam sections reveals that the carbonaceous matter present in the samples is enriched in trace metals (e.g., V, Cr, Fe, Co) and is associated with aromatic and aliphatic molecules, which strongly support its biological origin. Transmission electron microscopy observations of the carbonaceous matter documented an amorphous nanostructure interpreted to correspond to the degraded remains of microorganisms and their by-products (extracellular polymeric substances, filaments…). Nevertheless, a small fraction of carbonaceous particles has signatures that are more metamorphosed. They probably represent either reworked detrital biological or abiotic fragments of mantle origin. This study serves as an example of the analytical protocol that would be needed to optimize the detection of fossil traces of life in martian rocks.

Changes in the transformation of nitrogen and phosphorus under different microbial communities in sewage pipes.

Microbial communities living in different environments can affect the transformation of nitrogen and phosphorus in sewage pipes. Two different environments were simulated to investigate the differences in the transformation of nitrogen and phosphorus under different microbial communities in the pipe. Results showed that the concentration of nitrogen and phosphorus changed greatly in the first 25-33 days and the first 21 days, respectively, and then remained stable. The decrease in amino acid nitrogen (AAN) concentration and the increase in ammonia nitrogen (NH4 + -N) concentration in the sediments were evident in the contrast group. The concentrations of total phosphorus (TP), dissolved total phosphorus (DTP), and dissolved reactive phosphorus (DRP) in the overlying water and interstitial water decreased, and that of TP in the sediment increased. Some microorganisms in the sediments of both groups are related to the transformation of nitrogen and phosphorus, such as Clostridium_sensu_stricto_1, Sporacetigenium, Norank_f__Anaerolineaceae, Norank_f__norank_o__PeM15, and Caldisericum. The relative abundance of these microorganisms was remarkably differed between the two groups, which partly caused the difference in nitrogen and phosphorus transformation among overlying water, interstitial water, and sediment in the two environments. PRACTITIONER POINTS: The concentration of N and P changed greatly in the first 20-30 days. AAN and NH4 + -N in sediments had greater concentration variation in contrast group. In two groups, TP, DTP, and DRP of water decreased, and TP of sediment increased. Microbe related to the transformation of N and P differed between the two groups.

The combined effects of lanthanum-modified bentonite and Vallisneria spiralis on phosphorus, dissolved organic matter, and heavy metal(loid)s.

The use of lanthanum-modified bentonite (LMB) combined with Vallisneria spiralis (V∙s) (LMB + V∙s) is a common method for controlling internal phosphorus (P) release from sediments. However, the behaviors of iron (Fe) and manganese (Mn) under LMB + V∙s treatments, as well as the associated coupling effect on P, dissolved organic matter (DOM), and heavy metal(loid)s (HMs), require further investigations. Therefore, we used in this study a microelectrode system and high-resolution dialysis technology (HR-Peeper) to study the combined effects of LMB and V∙s on P, DOM, and HMs through a 66-day incubation experiment. The LMB + V∙s treatment increased the sediment DO concentration, promoting in-situ formations of Fe (III)/Mn (IV) oxyhydroxides, which, in turn, adsorbed P, soluble tungsten (W), DOM, and HMs. The increase in the concentrations of HCl-P, amorphous and poorly crystalline (oxyhydr) oxides-bound W, and oxidizable HMs forms demonstrated the capacity of the LMB + V∙s treatment to transform mobile P, W, and other HMs forms into more stable forms. The significant positive correlations between SRP, soluble W, UV254, and soluble Fe (II)/Mn, and the increased concentrations of the oxidizable HMs forms suggested the crucial role of the Fe/Mn redox in controlling the release of SRP, DOM, and HMs from sediments. The LMB + V∙s treatment resulted in SRP, W, and DOM removal rates of 74.49, 78.58, and 54.78 %, which were higher than those observed in the control group (without LMB and V∙s applications). On the other hand, the single and combined uses of LMB and V·s influenced the relative abundances of the sediment microbial communities without exhibiting effects on microbial diversity. This study demonstrated the key role of combined LMB and V∙s applications in controlling the release of P, W, DOM, and HMs in eutrophic lakes.

Microbial features with uranium pollution in artificial reservoir sediments at different depths under drought stress.

The uranium (U) containing leachate from uranium tailings dam into the natural settings, may greatly affect the downstream environment. To reveal such relationship between uranium contamination and microbial communities in the most affected downstream environment under drought stress, a 180 cm downstream artificial reservoir depth sediment profile was collected, and the microbial communities and related genes were analyzed by 16S rDNA and metagenomics. Besides, the sequential extraction scheme was employed to shed light on the distinct role of U geochemical speciations in shaping microbial community structures. The results showed that U content ranged from 28.1 to 70.1 mg/kg, with an average content of 44.9 mg/kg, significantly exceeding the value of background sediments. Further, U in all the studied sediments was related to remarkably high portions of mobile fractions, and U was likely deposited layer by layer depending on the discharge/leachate inputs from uranium-involving anthoropogenic facilities/activities upstream. The nexus between U speciation, physico-chemical indicators and microbial composition showed that Fe, S, and N metabolism played a vital role in microbial adaptation to U-enriched environment; meanwhile, the fraction of Ureducible and the Fe and S contents had the most significant effects on microbial community composition in the sediments under drought stress.

Distribution and ecological risk assessment of priority water pollutants in surface river sediments with emphasis on industrially affected areas.

Priority water pollutants comprising six plasticizers, 18 volatile organic compounds (VOCs), total petroleum hydrocarbon (TPH), 1,4-dioxane, epichlorohydrin, formaldehyde, acrylamide, and cyanides were determined in surface river sediments to assess their distribution patterns and ecological risks. Among these, di (2-ethylhexyl) phthalate (DEHP), toluene, TPH, and acrylamide were frequently found in sediments. The industrial sites had higher concentrations of ∑plasticizers (median 628 ng/g dry weight (dw)), ∑VOCs (median 3.35 ng/g dw), acrylamide (median 0.966 ng/g dw), and TPH (median 152 µg/g dw) in sediments than the mixed and non-industrial areas. The other pollutants did not show the significant differences in levels according to site types because of their relatively low detection frequencies. Volatile and soluble substances as well as hydrophobic pollutants were predominantly detected in surface sediments from industrial areas. Sediment contamination patterns were affected by the size and composition of the industrial zones around the sampling sites. The ecological risks determined using the sediment quality guidelines (DEHP, VOCs, and TPH) and the mean probable effect level quotients (DEHP) were mostly acceptable. However, the two most representative industrial regions (the largest industrial area and the first industrial city) showed risks of concern for DEHP and TPH.

PAH residues and toxicity levels two years after an extensive oil spill on the northeast Brazilian coast.

The most extensive oil spill ever recorded in tropical oceans occurred between August 2019 and March 2020, affecting approximately 3000 km of the Brazilian coast. This study assessed the chemical contamination and toxicity of sediments collected from affected reef areas during two sampling surveys conducted 17 and 24 months after the peak of oil slick inputs. Our results indicated that neither PAH levels nor measured toxicity showed a significant contribution from the spilled oil, with concentrations and biological effects indistinguishable from those in unaffected areas. Similarly, no differences were observed between seasons. Furthermore, there was no discernible relationship between sediment toxicity results and the measured PAH concentrations. Therefore, while biological responses indicated toxicity in most assessed areas, these responses are likely related to other local sources. This evidence suggests a natural oil attenuation process contributing to local environmental recovery. Nonetheless, further investigation is needed for other areas affected by oil spills.

Spatial dynamics and risk assessment of phosphorus in the river sediment continuum (Qinhuai River basin, China).

This study investigated the concentration and fractionation of phosphorus (P) using sequential P extraction and their influencing factors by introducing the PLS-SEM model (partial least squares structural equation model) along this continuum from the Qinhuai River. The results showed that the average concentrations of inorganic P (IP) occurred in the following order: urban sediment (1499.1 mg/kg) > suburban sediment (846.1-911.9 mg/kg) > rural sediment (661.1 mg/kg) > natural sediment (179.9 mg/kg), and makes up to 53.9-87.1% of total P (TP). The same as the pattern of IP, OP nearly increased dramatically with increasing the urbanization gradient. This spatial heterogenicity of P along a river was attributed mainly to land use patterns and environmental factors (relative contribution affecting the P fractions: sediment nutrients > metals > grain size). In addition, the highest values of TP (2876.5 mg/kg), BAP (biologically active P, avg, 675.7 mg/kg), and PPI (P pollution index, ≥ 2.0) were found in urban sediments among four regions, indicating a higher environmental risk of P release, which may increase the risk of eutrophication in overlying water bodies. Collectively, this work improves the understanding of the spatial dynamics of P in the natural-rural-urban river sediment continuum, highlights the need to control P pollution in urban sediments, and provides a scientific basis for the future usage and disposal of P in sediments.

Inhibitory effects and mechanisms of insoluble humic acids on internal phosphorus release from the sediments.

Release of phosphorus (P) from the sediments plays a critical role in the eutrophication of aquatic environments. Humic acids (HA), as the main form of carbon storage in the sediments, has essential impacts on the biogeochemical cycle of phosphorus in aquatic systems. Nevertheless, previous studies mainly concentrated on the competitive adsorption of HA solution and P on metal oxides and soils, with little attention paid to the effects of insoluble humic acids (IHA) on P sorption by and release from the sediments. Herein, an investigation on the rivers and lakes in Sichuan Province, China, found that there was a significantly positive correlation between the maximum P adsorption capacity (Qmax) of sediments and IHA contents (p < 0.01), but a significantly negative correlation between the zero equilibrium P concentration (EPC0) and IHA concentrations (p < 0.01). This indicated that IHA might have an inhibitory effect on the release of P from the sediments, which was verified by batch adsorption experiments and static incubation experiments. Adsorption experiments indicated that IHA can promote P adsorption by sediments. With the increase of IHA addition (from 0 to 20 mg/g) in the sediments, Qmax of sediments increased (from 0.516 to 0.911 mg/g), while EPC0 decreased greatly (from 0.264 to 0.005 mg/L). Increases in Fe (Ⅲ) bound-P, Al bound-P and humic bound-P caused by IHA were responsible for this promoting effect. Incubation experiments illustrated that IHA addition can efficiently inhibit P release from the sediments. After 32 days incubation, P concentration in the overlying water of control group (without IHA addition) was 0.651 mg/L, which was 13.29-40.69 times higher than those (0.016-0.049 mg/L) in the test groups (with 5 %-20 % IHA addition). The analysis of P species in sediments showed that transformation from loosely adsorbed-P and Fe (Ⅲ) bound-P to Al bound-P and humic bound-P was responsible for this inhibition of P release by IHA. This study demonstrated that IHA, differing from readily degradable or dissolved organic matter, have great inhibitory effects on internal P release, which provided a novel insight into the association between carbon burial and internal P release and even the management of water eutrophication.

Contrasting effects of MgAl- and MgFe-based layered double hydroxides on phosphorus mobilization and microbial communities in sediment.

The effects of two types of layered double hydroxides (LDH) in-situ treatment on sediment phosphorus (P) mobilization and microbial community's structure were studied comparatively. The results presented that magnesium/aluminum-based (MA) and magnesium/iron (MF)-based LDH displayed great phosphate uptake ability in aqueous solution in a broad pH range of 3-8. The maximum phosphate sorption capacity of MA was 64.89 mg/g, around four times greater than that of MF (14.32 mg/g). Most of phosphate bound by MA and MF is hard to re-liberate under reduction and ordinary pH (5-9) conditions. In the in-situ remediation, the MA and MF capping/amendment both prevented P migration from the sediment to the overlying water (OL-water) under long-term anaerobic conditions, and MA had a better interception efficiency compared to MF in the same application mode. MA amendment significantly reduced mobile P (Mob-P) content in sediment and could remain its stable Mob-P inactivation capacity over a wide pH range. On the contrary, MF amendment increased Mob-P content in sediment and exhibited a variable ability to inactivate Mob-P under elevated pH conditions. MF can decrease Mob-P content at pH of 7 and 11 but increase Mob-P content at pH of 8-10. Under resuspension conditions, MA and MF capping groups still maintained low P levels in OL-water, while MA capping simultaneously showed a certain degree of resistance to sediment resuspension, but it had a weaker stabilizing effect for sediment than MF. Microbial community analysis manifested neither MA nor MF addition observably altered the sediment microbial diversity, but impacted the functional microorganisms' abundance and reshaped the microbial community's structure, intervening the sediment-P stabilization. Viewed from environmental friendliness, control efficiency, stability of P fixation capacity, and application convenience, MA capping wrapped by fabric is more suitable for addressing internal P loading in eutrophic lakes and holds great potential application.

Impact of Eucalyptus residue leaching on iron distribution in reservoir sediments assessed by high-resolution DGT technique.

Blackwater occurs every winter in reservoirs with Eucalyptus plantations. The complexation reaction between ferric iron (Fe3+) and Eucalyptus leachate tannic acid from logging residues (especially leaves) is the vital cause of water blackness. However, the effect of Eucalyptus leaf leaching on the dynamic of iron in sediments and its contribution to reservoir blackwater remain unclear. In this study, two experiments were conducted to simulate the early decomposition processes of exotic Eucalyptus and native Pinus massoniana leaves in water (LW) and water-sediment (LWS) systems. In LW, high concentrations of tannic acid (>45.25 mg/L) rapidly leached from the Eucalyptus leaves to the water column, exceeding those of Pinus massoniana leaves (<1.80 mg/L). The chrominance increased from 5~10 to 80~140, and the water body finally appeared brown instead of black after the leaching of Eucalyptus leaves. The chrominance positively correlated with tannic acid concentrations (R=0.970, p<0.01), indicating that tannic acid was vital for the water column's brown color. Different in LWS, blackwater initially emerged near the sediment-water interface (SWI) and extended upward to the entire water column as Eucalyptus leaves leached. Dissolved oxygen (DO) and transmission values in the overlying water declined simultaneously (R>0.77, p<0.05) and were finally below 2.29 mg/L and 10%, respectively. During the leaching of Eucalyptus leaves, the DGT-labile Fe2+ in sediments migrated from deep to surface layers, and the diffusive fluxes of Fe2+ at the SWI increased from 12.42~19.93 to 18.98~26.28 mg/(m2·day), suggesting that sediment released abundant Fe3+ into the aerobic overlying water. Fe3+ was exposed to high concentrations of tannic acid at the SWI and immediately generated the black Fe-tannic acid complex. The results indicated that the supplement of dissolved Fe3+ from sediments is a critical factor for the periodic blackwater in the reservoirs with Eucalyptus plantations. Reducing the cultivation of Eucalyptus in the reservoir catchment is one of the effective ways to alleviate the reservoir blackwater.

Anthropogenic disturbances influence mineral and elemental constituents of freshwater lake sediments.

Lake sediments can provide valuable insights into anthropogenic disturbances such as intensive aquaculture and land use changes. These disturbances often manifest as elevated levels of nutrients and elements within the sediments. This paper uses several analytical techniques, i.e., FTIR (Fourier-transform infrared spectroscopy), XRD (X-ray diffraction), EDS (energy-dispersive X-ray spectroscopy), and SEM (scanning electron microscopy), to examine the elemental constituents of lake sediments, along with their relative mineral abundances and surface morphology. The selected freshwater lakes are from the Central Gangetic Plain. The analysis provides a "fingerprint" of geogenic and biogenic mineral constituents of the sediments. Physicochemical, mineralogical, and elemental analysis shows that intensive aquaculture activities in lake alter the sediment chemistry as evidenced by the increase in pH, organic carbon, organic matter, and total phosphorus which is not observed in the lake where aquaculture is prohibited. Freshwater lake sediment is characterized by a high content of biogenic silica and carbonate minerals. The variations in sediment nutrients and mineral fluxes of the selected lakes are mainly attributed to diverse anthropogenic pressures, differences in lake productivity, and the overall ecological condition of the lakes. In the selected three lakes, major variation was reported in the autochthonous sediments in comparison to the allochthonous sediments. The study concludes that catchment and biotic deposit variations in the lakes cannot be evened out by in-lake mixing mechanisms due to variations in the terrigenous and pelagic deposits of the lake. The results highlight the importance of studying annual fluctuations and spatial variations in geogenic and biogenic mineral particle fluxes in lakes. Such investigations provide valuable insights into the annual dynamics of minerals within lakes, contributing to a more comprehensive understanding of their behavior and distribution.

[Characteristics of Bacterial Community Structure in the Sediment of Rural Black and Odorous Water Bodies].

Sediment microorganisms are the main drivers of the material circulation and organic matter degradation processes in rural black and odorous water bodies(RBOWB), and the community structure of sediment microorganisms follows the changes in the external environment. Here, the pollutant indicators, including nitrogen, phosphorus, and heavy metals in the overlying water and sediment of 29 RBOWB in Dongming County of Heze City were measured, respectively. Combined with Illumina sequencing results, the composition and diversity characteristics of sediment bacterial communities in RBOWB and their correlation with environmental factors were further analyzed. The experimental results showed a wide distribution of pollutants in both of the overlying water and sediment in the RBOWB of this region. Compared with agricultural non-point source pollution, the concentrations of nitrogen and phosphorus pollutants in the overlying water with domestic sewage as the main source of pollution were 3.1 and 1.5 times higher than those of agricultural non-point source pollution, respectively. In addition, the contents of heavy metals in the sediments of RBOWB were generally lower than the soil element background value in Heze City. The dominant bacteria phyla in the sediments of the RBOWB were Proteobacteria, Actinobacteria, Chloroflexi, Firmicutes, and Acidobacteria, and the total abundance of these five dominant phyla accounted for 70.3%-83.6% of all sequences. The dominant classes were γ-Proteobacteria, α-Proteobacteria, Anaerolineae, and Actinobacteria. The dominant genera were Thiobacillus and Pseudarthrobacter. Moreover, Spearman correlation analysis showed that the environmental factors of DO, COD, TN, TP, and organic matter exerted significant effects(P<0.05) on sediment bacterial genera in RBOWB, and sediment bacterial community richness was significantly influenced by TN(P<0.05). The above results provided the microbiological knowledge for treating RBOWB.

Formation and sedimentation of oil-mineral aggregates in the presence of chemical dispersant.

The formation and sedimentation of oil-mineral aggregates (OMAs) is the major method to transport spilled oil to the seafloor. In this study, the formation and sedimentation experiments of OMA using montmorillonite and four crude oils were performed in a wave tank in the presence of chemical dispersant. Most of the formed OMAs were droplet OMAs, and single droplet OMA would aggregate into multiple ones under the action of the dispersant. The size of the oil droplets trapped in the OMA increased with time and was larger for the oil with higher viscosity. The sinking velocities of OMAs formed in this study were between 100-1200 µm s-1 and they were positively correlated with their diameter. The density of OMA was of the same order as that of the crude oil that formed them. An increase in the dispersant dosage could promote the formation of OMAs. The oil content in OMAs was higher for the denser oil in the presence of a dispersant. The maximum oil trapping efficiency of OMAs was 48.05%. This study provides fundamental data on the formation kinetics of OMAs.

[Spatial Distribution of Aerobic Bacteria, Sources and Risks of Nitrogen and Phosphorus in Taihu Lake Sediments].

The release of nitrogen and phosphorus from sediments into lake water will exacerbate the eutrophication of lakes and endanger ecological safety and human health. Microorganisms are indispensable in nitrogen and phosphorus conversion, and accurate analysis of the distribution characteristics and sources of nitrogen and phosphorus in sediments as well as their relationship with microorganisms is an important prerequisite for lake eutrophication control. Taking Taihu Lake as the study area, 30 surface sediment samples were collected, and the grain size, pH, organic matter (OM), dissolved organic carbon (DOC), total phosphorus (TP), total nitrogen (TN), nitrate nitrogen (NO3--N), and dissolved organic nitrogen (DON) along with some other index contents were measured and analyzed; accordingly, spatial distribution characteristics were analyzed. While using nutrient agar (NA), the number of aerobic bacteria (AB) was determined by plate counting in the medium. Combined with principal component analysis (PCA) and Pearson correlation analysis, the spatial distribution characteristics and sources of sediments and AB in Taihu Lake were explored. The characteristics of sediment pollution in Taihu Lake were studied using the comprehensive pollution index and the organic pollution index methods. The results revealed that the average sediment indicators of the surface layer of Taihu Lake were as follows:AB was 9.25×104 CFU·g-1, average particle size (MZ) was 17.59 µm, pH was 7.62, ω(OM) was 15.05 g·kg-1, ω(DOC) was 71.60 mg·kg-1, ω(TP) was 598.13 mg·kg-1, ω(TN) was 1113.92 mg·kg-1, ω(NO3--N) was 3.22 mg·kg-1, and ω(DON) was 22.60 mg·kg-1. The comprehensive pollution index (FF) showed that 13% of the Taihu Lake was moderately polluted, while 87% was heavily polluted. Excluding the area in the center of the lake, the southern lake area, and some lakes in the western part of the East Taihu Lake, TN in the rest of the area was moderately and severely polluted. In addition to the heavy pollution of Zhushan Bay, the TP in Taihu Lake was generally at light and moderate pollution. The organic pollution index (OI) showed that the organic pollution of the sediments of Taihu Lake was relatively light, majorly caused by organic nitrogen (ON) pollution. DOC, DON, TN, and OM in Taihu Lake were primarily derived from the influence of aquatic plants, and TP And AB were primarily derived from the influence of the external input of rivers. This research will provide theoretical support for lake eutrophication treatment and also provide new ideas for further analysis of AB to remove nitrogen and phosphorus pollution from sediments.

Immobilization of phosphorus in water-sediment system by iron-modified attapulgite, calcite, bentonite and dolomite under feed input condition: Efficiency, mechanism, application mode effect and response of microbial communities and iron mobilization.

Four kinds of iron-based materials, i.e., iron-modified attapulgite, calcite, bentonite and dolomite (abbreviated as Fe-ATP, Fe-CA, Fe-BT and Fe-DOL, respectively) were prepared and used to immobilize the phosphorus in the system of overlying water (O-water) and sediment under the feed input condition, and their immobilization efficiencies and mechanisms were investigated. The influence of application mode on the immobilization of phosphorus in the water-sediment system by Fe-ATP, Fe-CA, Fe-BT and Fe-DOL was researched. The effects of Fe-ATP, Fe-CA, Fe-BT and Fe-DOL on the concentration of labile iron in the water-sediment system and the microbial communities in sediment were also studied. The results showed that the Fe-ATP, Fe-CA, Fe-BT and Fe-DOL addition all can effectively immobilize the soluble reactive phosphorus (SRP), dissolved total phosphorus (DTP) and diffusive gradients in thin-films (DGT)-labile phosphorus in O-water under the feed input condition, and also had the ability to inactivate the DGT-labile phosphorus in the top sediment. Although the change in the application mode from the one-time addition to the multiple addition reduced the inactivation efficiencies of SRP and DTP in O-water in the early period of application, it increased the immobilization efficiencies in the later period of application. Although Fe-ATP, Fe-CA, Fe-BT and Fe-DOL had a certain releasing risk of iron into the pore water, they had negligible risk of iron release into O-water. The addition of Fe-ATP, Fe-CA, Fe-BT or Fe-DOL reshaped the sediment bacterial community structure and can affect the microorganism-driven phosphorus cycle in the sediment. Results of this work suggest that Fe-ATP, Fe-CA, Fe-BT and Fe-DOL are promising phosphorus-inactivation materials to immobilize the phosphorus in the water-sediment system under the feed input condition.

Effects of switching redox conditions on sediment phosphorus immobilization by calcium/aluminum composite capping: Performance, ecological safety and mechanisms.

There many materials were used in lake restoration to immobilize phosphorus (P) and reduce the effect of eutrophication. Among them, calcium/aluminum composite (CAC) showed a good capacity of P adsorption. However, a comprehensive of its performance, ecological safety, and the mechanism of P passivation in the aluminum-bound P (Al -P) dominated sediments under varying redox conditions remains incomplete. In the current study, both unwashed CAC (UCAC) and washed CAC (WCAC) showed good P adsorption properties, and the greatest maximum capacity for P adsorption (Qmax) reached 206.8 mg/g at pH 8.5 for UCAC. The SRP and TP in the overlying water of the uncapped sediments showed a decrease-increase-decrease trend in a sequence of transition from aerobic to anaerobic to re-aerobic stages. In contrast, the SRP and TP of the two CACs-capped sediments were maintained low. Phosphorus forms in the uncapped sediment also underwent significant changes during continuous variation of dissolved oxygen (DO) levels. In particular, the decrease in iron-bound P (Fe-P) and Al-P was significantly promoted in the anaerobic phase, and the released P was reabsorbed to form mainly Fe-P in the re-aerobic phase. The CACs-capping promoted the transformation of Fe-P to residual P (Res-P), forming a thick static layer in the surface sediment, thus significantly inhibiting sediment P release. Moreover, the CACs-capping did not induce the Al3+ leaching and significant changes of the microbial community in sediments, and their performances of P immobilization could keep stable to resist the redox variation, which promised to be a good choice for P passivation in eutrophic lake sediments dominated by Al/Fe-P. These findings also confirmed that the risk of P release from Al/Fe-P (mainly Al-P)-dominated sediments was strongly influenced by continuously changing redox conditions, and was probably enhanced by the formation of Fe-P from the resorption of the released P.

Recognizing the variation of DNA-P during and after the algal bloom in lake Hulun.

Eutrophication has spread from shallow lakes in temperature zones to lakes in cold regions as a result of a continuous warm climate and human activities. Little proof for the importance of dissolved organic phosphorus (DOP) in contributing to phosphorus cycling and algae growth has been generated for aquatic ecosystems, particularly in cold eutrophic lakes. In this study, a comprehensive in situ study was conducted in overlying water, suspended particulate matter, and sediment during and after algal bloom (in July and September, respectively) in Lake Hulun. Multiple methods of 31P NMR, enzymatic hydrolysis, and UV-visible technologies were combined to detect phosphorus occurrence, bioavailability, and molecular structure from a novel angle. The 31P NMR analysis results showed that DNA-P is mainly stored in the dissolved phase and has not been detected in suspended particulate matter or sediment. Enzymatic hydrolysis was used to determine the bioavailability of DOP, which revealed that in July and September, respectively, 85% and 79% of DOP were hydrolyzable. UV-visible analysis represented that the degree of humification and molecular weight of DOP were high during the algal bloom, but these values considerably dropped following the algal bloom. The large amount of DNA-P present in the overlying water is the main reason for the high degree of humification and high molecular weight of the water body. Besides, Lake Hulun's DNA-P remains highly bioavailable during algal blooms, despite its high degree of humification and molecular weight. These findings can serve as a theoretical basis for understanding the migration and transformation of DOP, as well as the persistence of algal blooms in eutrophic lakes located in cold regions.

Coupled Processes Involving Organic Matter and Fe Oxyhydroxides Control Geogenic Phosphorus Enrichment in Groundwater Systems: New Evidence from FT-ICR-MS and XANES.

The enrichment of geogenic phosphorus (P) in groundwater systems threatens environmental and public health worldwide. Two significant factors affecting geogenic P enrichment include organic matter (OM) and Fe (oxyhydr)oxide (FeOOH). However, due to variable reactivities of OM and FeOOH, variable strategies of their coupled influence controlling P enrichment in groundwater systems remain elusive. This research reveals that when the depositional environment is enriched in more labile aliphatic OM, its fermentation is coupled with the reductive dissolution of both amorphous and crystalline FeOOHs. When the depositional environment is enriched in more recalcitrant aromatic OM, it largely relies on crystalline FeOOH acting concurrently as electron acceptors while serving as "conduits" to help itself stimulate degradation and methanogenesis. The main source of geogenic P enriched by these two different coupled processes is different: the former is P-containing OM, which mainly contained unsaturated aliphatic compounds and highly unsaturated-low O compounds, and the latter is P associated with crystalline FeOOH. In addition, geological setting affects the deposition rate of sediments, which can alter OM degradation/preservation, and subsequently affects geochemical conditions of geogenic P occurrence. These findings provide new evidence and perspectives for understanding the hydro(bio)geochemical processes controlling geogenic P enrichment in alluvial-lacustrine aquifer systems.