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Photochemically generated reactive oxygen species (ROS) are widespread on the earth's surface under sunlight irradiation. However, the nonphotochemical ROS generation in surface water (e.g., paddy overlying water) has been largely neglected. This work elucidated the drivers of nonphotochemical ROS generation and its spatial distribution in undisturbed paddy overlying water, by combining ROS imaging technology with in situ ROS monitoring. It was found that H2O2 concentrations formed in three paddy overlying waters could reach 0.03-16.9 µM, and the ROS profiles exhibited spatial heterogeneity. The O2 planar-optode indicated that redox interfaces were not always generated at the soil-water interface but also possibly in the water layer, depending on the soil properties. The formed redox interface facilitated a rapid turnover of reducing and oxidizing substances, creating an ideal environment for the generation of ROS. Additionally, the electron-donating capacities of water at soil-water interfaces increased by 4.5-8.4 times compared to that of the top water layers. Importantly, field investigation results confirmed that sustainable •OH generation through nonphotochemical pathways constituted of a significant proportion of total daily production (>50%), suggesting a comparable or even greater role than photochemical ROS generation. In summary, the nonphotochemical ROS generation process reported in this study greatly enhances the understanding of natural ROS production processes in paddy soils.

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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.

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Sediments act as sinks of microplastics (MPs) derived from terrestrial ecosystems. However, the fate and transport of MPs at the zone of sediment-overlying water in reservoir environment are poorly understood. Here, the MPs distribution patterns in surface sediments of the Three Gorges Reservoir (TGR) and dominant mechanisms responsible for the sinking of MPs at the zone of sediment-overlying water were comprehensively investigated. The predominant occurrence of small microplastics (<300 µm, SMPs) in surface sediments of the TGR was found, with buoyant polyethene (PE) was dominant polymer types. Interestingly, the high abundance of SMPs in sediments correlated well with the Ca2+/Mg2+ in overlying water, suggesting that divalent cations in overlying water may enhance the preferential deposition of SMPs. Simulation sinking experiments under the presence of Microcystis aeruginosa and two divalent cations using different-sized PE MPs demonstrated that the greater deposition of SMPs was mainly the result of the formation of biogenic calcite on the surface of MPs rather than magnesium minerals, which provides stronger ballasting effects for SMPs than for large MPs. This study first highlights that the impact of biomineralization on preferential sinking of SMPs and enhances the understanding of the transport behaviour of MPs in aquatic environment.

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In order to explore the occurrence characteristics of microplastics in the freshwater environment of Baiyangdian Lake in China, ten overlying water samples and ten sediment samples were collected in Baiyangdian Lake of Hebei Province in October 2021, and the abundance distribution, shape, particle size, and polymer type of microplastics in the samples were identified using laboratory pretreatment, microscope observation, and laser infrared spectroscopy. The sedimentation law of microplastics at the overlying water-sediment interface was studied using the Stokes sedimentation formula, and their pollution characteristics and potential sources were analyzed. The abundances of microplastics in the overlying water and sediments in Baiyangdian Lake ranged from 474-19382 n·m-3 and 95.3-29542.5 n·kg-1, respectively, with an average value of 6255.4 n·m-3 and 11088 n·kg-1. The main polymer of the microplastics in the overlying water was polyethylene terephthalate[PET, (17.20±0.26)%], and the microplastics in the sediments were mainly chlorinated polyethylene[CPE, (46.11±1.30)%]. The sedimentation velocities of microplastics in the sedimentation zone ranged from 0.0793-111.7547 mm·s-1. The particles with larger particle size had higher sedimentation velocity and easily settled and remained in the sediments. The main sources of microplastic pollution in the study area were the discharge of textile fibers from washing wastewater and the wear and tear of ship paint, ship rubber, and building materials.

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Sedimentary organic matter provides carbon substrates and energy sources for microorganisms, which drive benthic biogeochemical processes and in turn modify the quantity and quality of dissolved organic matter (DOM). However, the molecular composition and distribution of DOM and its interactions with microbes in deep-sea sediments remain poorly understood. Here, molecular composition of DOM and its relationship with microbes were analyzed in samples collected from two sediment cores (∼40 cm below the sea floor), at depths of 1157 and 2253 m from the South China Sea. Results show that niche differentiation was observed on a fine scale in different sediment layers, with Proteobacteria and Nitrososphaeria dominating the shallow sediments (0-6 cm) and Chloroflexi and Bathyarchaeia prevailing in deeper sediments (6-40 cm), indicating correspondence of microbial community composition with both geographical isolation and the availability of organic matter. An intimate link between the DOM composition and microbial community further indicates that, microbial mineralization of fresh organic matter in the shallow layer potentially resulted in the accumulation of recalcitrant DOM (RDOM), while relatively low abundance of RDOM was linked to anaerobic microbial utilization in deeper sediment layers. In addition, higher RDOM abundance in the overlying water, as compared to that in the surface sediment, suggests that sediment might be a source of deep-sea RDOM. These results emphasize the close relation between the distribution of sediment DOM and different microbial community, laying a foundation for understanding the complex dynamics of RDOM in deep-sea sediment and water column.

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Resuspension is a crucial process for releasing endogenous pollution from shallow lakes into the overlying water. Fine particle sediment, which has a higher contamination risk and longer residence time, is the primary target for controlling endogenous pollution. To this end, a study coupling aqueous biogeochemistry, electrochemistry, and DNA sequencing was conducted to investigate the remediation effect and microbial mechanism of sediment elution in shallow eutrophic water. The results indicated that sediment elution can effectively remove some fine particles in situ. Furthermore, sediment elution can inhibit the release of ammonium nitrogen and total dissolved phosphorous into the overlying water from sediment resuspension in the early stage, resulting in reductions of 41.44 %-50.45 % and 67.81 %-72.41 %, respectively. Additionally, sediment elution greatly decreased the concentration of nitrogen and phosphorus pollutants in pore water. The microbial community structure was also substantially altered, with an increase in the relative abundance of aerobic and facultative aerobic microorganisms. Redundancy analysis, PICRUSt function prediction, and the correlation analysis revealed that loss on ignition was the primary factor responsible for driving changes in microbial community structure and function in sediment. Overall, the findings provide novel insights into treating endogenous pollution in shallow eutrophication water.

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Heavy metals in reservoir sediments were analyzed to assess the pollution level and to understand the potential risk on water supply safety. Heavy metals in sediments will enter the biological chain through bio-enrichment and bio-amplification in water and eventually pose a threat to the safety of drinking water supply. Analysis of eight sampling sites in JG (Jian gang) drinking water reservoir of the sediments showed that from Feb 2018 to Aug 2019 heavy metals including Pb, Ni, Cu, Zn, Mo, and Cr increased by 1.09-17.2%. Vertical distributions of heavy metals indicated that the concentrations increased gradually by 9.6-35.8%. Risk assessment code analysis indicated that Pb, Zn, and Mo were of high risk in the main reservoir area. What is more, enrichment factors of Ni and Mo were 2.76-3.81 and 5.86-9.41, respectively, showing the characteristics of exogenous input. The continuous monitoring results of the bottom water showed that the concentration of heavy metals in the bottom water exceeded the environmental quality standard value of surface water in China, and exceeded the standard by 1.76 times (Pb), 1.43 times (Zn), and 2.04 times (Mo), respectively. Heavy metals in the sediments of JG Reservoir, especially in the main reservoir area, have a potential risk of release from the sediment to the overlying water. Water supply reservoir as a source of drinking water, its quality is directly related to human health and production activities. Therefore, this first study on JG Reservoir is of great significance for the protection of drinking water safety and human health.

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To further understand the purification mechanism of antimony (Sb) in reservoirs, samples of stratified water and bottom interface sediment were collected in this study. The cross-flow ultrafiltration technique was used to separate the truly dissolved (<1 kDa) and colloidal (1 kDa-0.45 µm) phases of water, and two modified sequential extraction techniques were used to determine the Sb and Fe mineral forms in sediment, respectively. The results showed that the total Sb concentration could decrease from 142.2 µg/L in surface water to 98.6 µg/L at 16 m; this was contributed to by the removal of truly dissolved Sb. In comparison to particulate Sb (>0.45 µm), the formation of colloidal Sb played a greater role in the purification process. There was a positive correlation between Sb and Fe in the colloidal phase (r = 0.45, P < 0.05). The generation of colloidal Fe could be promoted by higher temperatures, pH values, DO, and DOC in the upper layer (0-5 m). However, the complexation of DOC with colloidal Fe inhibited the adsorption of truly dissolved Sb. After entering the sediment, the secondary release of Sb could not increase the Sb concentration in the lower layer obviously, while the supplementation of Fe(III) could further enhance Sb natural purification.

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Molybdenum (Mo) sourced mainly from artificial activities is an emerging environmental concern whose remediation is seldom reported. This study screened the Mo-enriched macrophyte Vallisneria natans (Lour.) Hara due to its high enrichment factor (10.25). Phytoremediation (V. natans) and microorganism-assisted phytoremediation (V. natans-Serratia marcescens A2) efficiency were compared. S. marcescens A2 improved phytoremediation in the early stage, however, it reduced the total Mo removal rate by 8.42%. Further experiments were conducted to investigate the environmental factors (light intensity and overlying water flow rate) on the phytoremediation by V. natans. The optimal phytoremediation performance was achieved under a high overlying water flow rate (0.022 cm·s-1) with intense light (60 µmol·m-2·s-1) conditions. In addition, increasing the light intensity or flow rate increased the microbial communities' diversity in the sediment. Notably, the abundance of norank_f__Bacteroidetes_vadinHA17, related to Mo release in sediments, increased by 147.96% at optimal conditions. This study illustrated that the phytoremediation of Mo-contaminated sediments by V. natans is of practical potential.

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Under the influence of environmental change, disturbance and other external conditions, sediments release internal nutrients to the overlying water and become a contamination source in the lake. Complex habitat systems provide a unique opportunity for determining the influences of environmental changes in lakes. In this study, Baiyangdian Lake (BYDL) was divided into different habitat systems (connected water areas, river courses, reed fields, lotus ponds, fishponds, farmland, and thorps) based on the influence of natural and artificial activities. The physical and chemical properties of overlying water and sediment in different habitat systems were investigated. In addition, statistical analytical methods were used to analyze the relationship between sediment characteristics and overlying water parameters in different habitat systems. The results showed that nitrogen and phosphorus in the overlying water could accumulate in the sediments, while disturbance was one of the main factors affecting the release of nutrients from sediments. Disturbance promoted the suspension of sediments and increased the oxygen content, thereby facilitating the internal release of nutrients. However, there were also some differences in the process of internal release of nutrients between the habitat systems. Nitrogen in the overlying water was closely related to the source of organic matter (r > 0.950), especially in the ponds (including lotus ponds, reed fields, and fishponds), and phosphorus was mainly influenced by turbidity (r > 0.870). In the river course (p = 0.198, n = 26), the disturbance and increase in pH promoted the internal release of nutrients from the sediments (contributions of 35.2 % and 25.1 %, respectively). In the ponds, the aquatic macrophytes reduced the release of nitrogen and phosphorus in sediments. Overall, this study provides more information on the migration and transformation of nutrients between sediment and overlying water in lakes with multiple habitats.

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Porewater is the primary carrier of sediment nitrogen and a crucial source of overlying water nitrogen; its separation thus is essential for restraining nitrogen release from sediment to overlying water. We developed a novel device using electrokinetic geosynthetics to drain porewater with nitrogen and restrain nitrogen release. A batch experiment lasted 1120 h (about 47 days) was conducted with 20 cm depth of overlying water under three conditions, i.e., undrained at 0 V/cm voltage gradient (control), drained at 0 V/cm, and drained at 0.5 V/cm. Under the pulsed direct current, once porewater drained, overlying water replenished sediment pore space and supplied porewater. Along with porewater drainage, sediment nitrogen concentration was reduced by 11%-30%, decreasing nitrogen release from sediment to overlying water from 83 mg/m2 in the first 100 h to -95 mg/m2 after about 600 h. Processes such as electroosmosis, electromigration, and redox reaction contributed to the restraint on nitrogen release. This research revealed the potentiality of applying electrokinetic geosynthetics to in-situ restraint on sediment nitrogen release in eutrophic waterbodies such as fishponds.

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The unique operation mode of the Three Gorges Dam has determined that the tributaries of the Three Gorges Reservoir (TGR) are significantly different from natural rivers in terms of hydrodynamics. The aim of this study was to explore the dynamic changes of internal phosphorus in tributary sediments under special water transfer mechanisms in the reservoir area. In 2016, we conducted samplings eight times (January, March-August, and October, once a month) in the Gaoyang Lake, which is located in the middle section of the Pengxi River, the largest tributary in the northern bank of the TGR. Samples of the adjacent overlying (AOL) water and sediment were collected, and a series of analyses were carried out on the flow velocity, water depth, and alkaline phosphatase activity (APA) of sediments. The results indicated that the waterbody types of the Gaoyang Lake can be divided into two hydrological states:deep lakes before May and June and typical rivers from May and June until the Three Gorges Dam re-flooding in autumn. The concentration of dissolved phosphorus in the AOL water during the lake state was 42.48% higher than that in the river state, which was beneficial for the weakly bounded phosphorus (NH4Cl-P) in the sediment surface to be in an adsorption-releasing equilibrium state. At the beginning of the spring algal bloom, with the increase in water temperature and APA in the sediments, the content of potential mobile phosphorus (PMP) in the sediments increased; however, the stable-form phosphorus content decreased, showing a tendency of transformation between these two forms of phosphorus, which may be one of the available phosphorus sources for algal blooms. The stable-form phosphorus content in the sediments of the Gaoyang Lake accounted for approximately 81.79% of the total phosphorus content, its coefficient of variation was relatively small (2.90%-4.21%), and there was a significant trend of accumulation over time (P<0.05). The study revealed the transformation of different phosphorus forms in sediments and their relationship with the state shift of the waterbodies, and provided a reference to understand the internal phosphorus cycle in other tributaries of the TGR area or other reservoir tributaries under similar situations.

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Overlying water with suspended particles is a hot spot for nitrogen removal in river systems. Although light exposure affects nitrogen transformations and nitrogen removal in some environments, such effects have rarely been explored and quantified in riverine overlying water. Herein, we examined the difference between dark and light conditions in the community composition and abundance of nitrogen transformation microbes in simulated overlying water by high-throughput sequencing and qPCR. Moreover, 15N-labeling techniques were used to investigate variation in nitrogen removal rates (N2 and N2O) as well as nitrification rates between dark and light conditions. We found apparent differences in the bacterial community between light and dark microcosms. The abundance of Cyanobacteria was greatly elevated in light microcosms, with the diazotroph nifH gene abundance being 7.4-fold higher in the light microcosm (P < 0.01). However, due to the vulnerability of some specifies to UV damage, the diazotroph species richness was reduced. The abundances of ammonia-oxidizing archaeal amoA, ammonia-oxidizing bacterial amoA, and denitrifying nirS genes were 80.1%, 46.3%, and 50.7% lower in the light microcosm, respectively, owing to the differential inhibition of sunlight exposure on these microbes. Both 15N-N2 and 15N-N2O were significantly produced regardless of conditions with or without light. Due to the combined effects of reduced nitrification and denitrification, as well as potentially enhanced nitrogen fixation, the accumulated amounts of 15N-N2 and 15N-N2O were 6.2% and 44.8% lower, respectively, in the light microcosm. This study quantifies the inhibitory effect of sunlight exposure on nitrogen removal in riverine overlying water and reveals the underlying mechanisms, providing insights into our understanding of nitrogen transformations in river systems.

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The water quality in the sewer systems can be significantly influenced by the interaction between sediment and overlying water, which are still many doubts about the impact of pollutants transformation, degradation sequence, and reaction time. In this study, the exchanging processes between sewer sediment and four different overlying waters were evaluated in simulated urban sewer systems (dark and anaerobic environments). Dissolved organic matter (DOM) was used as an indicator to reflect the mitigation and exchange processes of pollutants. Excitation-emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) as an effective method for deciphering DOM properties was applied. There are three findings: (1) Three main processes (biological degradation, desorption, and adsorption) happened in the simulated sewer systems, in which the predominant pathway in the interaction process is biological degradation though consuming amino acid components. (2) The characteristics of overlying water could induce significant changes in sediment signatures; the amino acid-like components are more susceptible to degradation, and the humic-like compositions are more readily absorbed by sediments. (3) The reaction time is another significant factor (14 days was the turning point of the processes). This study unravels the transformation processes in sediment and different overlying waters, which provides the theoretical foundation for urban sewer efficient management and operation.

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Heavy metal pollution in lake systems has arisen plenty of threats for public health because of its high toxicity, persistence, and bioaccumulation. Whereas heavy metals are inextricably linked with bioavailability in pore water and overlying water. Lake Jiaogang is classified as an important water-carrying lake situated in the northern part of the Anhui Province China. In recent years, water quality in this lake declined due to increasing fishery aquaculture, livestock, and tourism. This study aims to bring insight into the interactions of heavy metal elements across sediment-water interface in Lake Jiaogang. Four representative regions were selected, more than ten heavy metals were chosen to quantify by the Community Bureau of Reference, diffusive gradient in thin-film (DGT), and high-resolution pore water equilibrators. The results showed that most heavy metals corresponded with the reducible fraction, acid-soluble fraction, and oxidizable fraction in the Eastern area (sample 3#) and aquaculture area (sample 4#) were higher than that of emergent plant area (sample 1#), and floating plant area (sample 2#). The average fluxes of heavy metals (except Ni and Zn in sample 3#, F value > 0 pg/cm2/d) in the four sampling sites were observed in the lower reaches (F value < 0 pg/cm2/d). The vertical distribution of heavy metals was extracted by DGT, such as As (exclude 2#), Co, Fe, Mn, and Zn (contain 4#) showed an increased content with increasing depth in the four sampling sites. In the pore and overlying water, concentrations of heavy metals from the sample 3# and 4# were higher than those of sample 1# and 2#. Heavy metal pollution in anthropogenic activity areas was higher than those in areas with ecological vegetation, and risk control in this area should be strengthened.

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In order to reveal the interaction of overlying water-interstitial water nitrogen and phosphorus nutrient salt in summer at the entrance region of Baiyangdian Lake, this study sampled six main rivers in the region during July 2019. An analysis of the overlying water and interstitial water quality characteristics and the diffusion flux of applied nutrients at the sediment-water interface revealed the effects of nutrient diffusion on sediments and overlying water. The overlying water analysis showed that the water quality was slightly alkaline in the Baiyangdian Lake. The content of dissolved oxygen (DO) was lower, which provided an anaerobic environment for the release of endogenous pollutants from sediments. The ammonia nitrogen (NH4+-N) ranged from 0.35 to 1.76 mg·L-1, and the content of ammonia nitrogen was the highest in the Zhulong River, which was the main source of water supply. The nitrate nitrogen (NO3--N) content ranged from 0.75 to 1.97 mg·L-1. The total dissolved nitrogen (TDN) ranged from 0.99 to 2.70 mg·L-1, and the content of TDN was the highest in Puhe River. The content of total dissolved phosphorus (TDP) was 0.03 to 0.15 mg·L-1, and the content of TDP was the highest was Baigouyin River, which is near the residential area. The results indicated that the content of ammonia nitrogen in the interstitial water was between 5.24 and 10.64 mg·L-1, which was 10 times that of the overlying water, and endogenous pollution in the former was severe. The nitrate nitrogen content ranged from 0.36 to 0.79 mg·L-1. The total dissolved nitrogen content was between 5.36 and 12.02 mg·L-1, which was 5 times higher than that of the overlying water. The total dissolved phosphorus was between 0.03 and 0.3 mg·L-1. According to integrated pollution index, the degree of interstitial water pollution was much higher than that of overlying water, and the sampling points are seriously polluted. The exchange flux analysis of NH4+-N, TDN, and TDP demonstrated that the diffusion flux of NH4+-N was between 1.71 and 7.43 mg·(m2·d)-1, and the diffusion rate of endogenous ammonia nitrogen to the overlying water was fastest in Fu River, the absorbing river in Baoding. The diffusion flux of total dissolved nitrogen was lower in the Baigouyin River, and the other five sample points averaged 9.11 mg·(m2·d)-1. In summer, the dissolved oxygen was lower and the water-sediment had a larger concentration difference, which led to massive nitrogen nutrient of sediment in anaerobic conditions released to the overlying water in great quantities that caused the serious pollution. The diffusion flux of dissolved total phosphorus showed that the sediment of Pinghe River acted as a "sink" of phosphorus nutrients, and the other sampling points ranged from 0.03 to 0.16 mg·(m2·d)-1, showing the state of phosphorus nutrient released upward to the overlying water. Finally, diffusion flux indicated that endogenous pollutants are crucial sources of overlying water pollutants. In order to effectively control the water quality in the entrance area, desilting the nitrogen and phosphorus nutrient salt of sediment is urgently required.

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In this study, indoor simulation experiments were performed to elucidate the effects of migration and transformation of dissolving organic matter (DOM) during the decay of algal blooms. Based on ultraviolet-visible spectra (UV-vis) and excitation-emission matrix spectroscopy (EEMs), spectral characterizations of dissolved organic matter (DOM) in overlying water were evaluated with analyses of the physical and chemical indexes, variation in dissolved organic carbon (DOC), and variation in dissolved inorganic carbon (DIC). Results showed that at the early stage of decay, a large amount of organic matter was released, and dissolved oxygen (DO) decreased sharply. With the extension of reaction time, DOC gradually changed into DIC, which further changed the oxidation-reduction and acid-base characteristics of the water. UV-vis spectra showed that a large amount of DOM was released with high aromaticity and a high degree of humification, and the released DOM was gradually degraded. With the application of parallel factor analysis in excitation-emission matrix spectroscopy (EEM-PARAFAC), three fluorescence components were analyzed:refractory humic-like substances (C1), protein-like tryptophan substances (C2) produced by algae, and fulvic-like substances (C3) related to microbial activities. Most protein-like tryptophan substances were degraded into fulvic-like substances by microorganisms during the decaying process. Heterotrophic microorganisms promoted the release of algae-derived DOM and accelerated the degradation of DOM. The DOM born during algae blooms decaying process was eventually converted into humic-like substance, which was difficult to be degraded. We analyzed correlations of water quality, UV-vis spectrum, and EEMs parameters. Results showed that ORP was positively correlated (P<0.05) with DO. There was a significant negative correlation (P<0.05) between pH and DOC, which was consistent with the trend of the transformation to from DOC to DIC; C1 was positively correlated (P<0.05) with Fn355; and C2 was significantly positively correlated (P<0.05) with DOC and Fn280; C3 was positively correlated (P<0.05) with FI, BIX and ß:α. The variation trend of these spectral parameters was consistent with that of DOM components. In summary, with the analyses of water quality characteristics and spectral characteristics of DOM in overlying water during algae blooms decaying process, it was expected that our results could contribute to the further exploration of the dynamic migration and transformation of lake DOM and the changes of carbon cycling.

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The composition and structure of dissolved organic matter (DOM) play vital roles in the material cycle of river ecosystems. Based on ultraviolet-visible absorption spectroscopy, excitation-emission matrix fluorescence spectroscopy, and ultrahigh-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry technology, this study comprehensively characterized the composition and structure of DOM in the overlying water of the Chaobai River in order to determine the potential environmental impact of DOM on the water quality. The results showed that the DOM content of the overlying water in the Chaobai River was between 10.94 and 28.13 mg/L. The main DOM component of the overlying water was humus (70.94%). The relative abundance of CHOS compounds in the Chaobai River was lower than Maozhou River (urbanized river) and significantly higher than Xiangxi Bay (suburban river). In addition, the DOM composition and structure of the overlying water were closely related to anthropogenic input, microbial activity, and phytoplankton. In particular, chlorophyll a can indirectly reflect fresh autochthonous DOM content and composition in the overlying water. The results of this study further reveal the characteristics of suburban rivers and provide theoretical basis and guidance for the water quality evaluation and pollution control of the Chaobai River and other suburban rivers worldwide.

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Migration and release of sediment pollutants has become one of the important causes of water pollution, but the contribution of different forms of nitrogen in different water layers to the water quality of the overlying water is unclear. In this study, the main stream of Liaohe River with heavy nitrogen pollution was taken as an example. The static simulation method and related analysis techniques were used to explore the release characteristics of different forms of inorganic nitrogen and its effect on TN and Chla in overlying water from the different water layers. The results showed that the release rates of TN, NH4+-N and NO3--N from upstream, midstream and downstream sections were different, but the release characteristics of them in different water layers were the same basically. Generally, the inorganic nitrogen in the pore water of the sediment was released to the water body rapidly in the early 0-8 days. The contribution rate of NH4+-N and NO3--N to the change of TNo was 76.85% for the upstream section, and the contribution rate of NO3--N to the change of TNo was 65.02% for the midstream section. NH4+-N and NO3--N in the different water layers from downstream did not showed a significant correlation with TN of overlying water. NO3--N in sediments was the main contributor of TN and Chla changes in the overlying water and its content can reflect the nitrogen pollution trend of the water body to a certain extent. When the water retention time was 4-16 days, the TLI in the water body was relatively high. After effective control of exogenous pollution, the release of endogenous nutrients in Liaohe River should be paid more attention.

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Release of contaminants from sediments has been one of the main pollution sources causing eutrophication and malodorous black of ponds. In this study, an iron-rich substrate (IRS) was developed based on iron­carbon micro-electrolysis and applied for simultaneous sediments and overlying water remediation. IRS obtained high ammonia and phosphate adsorption capacities (Langmuir isotherm) of 13.02 and 18.12 mg·kg-1, respectively. In the 90-day long-term remediation, IRS reduced NH4+-N, PO43--P, organic-N, organic-P, TN and TP in overlying water by 48.6%, 97.9%, 34.2%, 67.1%, 53.2% and 90.4%, respectively. In sediments, IRS reduced NO3--N, NH4+-N and organic-N by 98.5%, 26.5% and 6.3%, respectively. The unstable P-compounds (i.e., organic-P, Ca-bounded-P and labile-P) were effectively transferred (20.1%, 54.3% and 98.2%, respectively) into inert P-compounds (i.e., Fe-bounded-P and residual-P). Meanwhile, flux rates of nitrogen and phosphorus from sediments to overlying water were reduced from 7.02 to 4.92 mg·m-2·d-1 (by 29.9%) and from 7.42 to 2.21 mg·m-2·d-1 (by 70.2%), respectively. Due to micro-electrolysis, Fe2+/Fe3+/[H] were in-situ generated from IRS and NO3--N was effectively reduced. Additionally, the generation of O2· was promoted by Fe2+/[H] and strengthened the NH4+-N, organic-N/P oxidation. Fe3+ enhanced the immobilization of PO43- (e.g., as FePO4·H2O and FenPO4(OH)3n-3). The released Fe2+/Fe3+ from IRS were finally stabilized as poorly reactive sheet silicate (PRS)-Fe and magnetite-Fe in the sediments and hardly showed side effect to sediments and water body. The developed IRS obtained advantages of high efficiency, ecologically safe and cost-effective in contaminated sediments and overlying water remediation.