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This study provides nanoscale and molecular-scale evidence that the formation, stability, and transport of NOM–Cr(iii) colloids depend on the C/Cr ratio and NOM source.

The transport and retention of microorganisms are typically described using attachment/detachment and straining/liberation models. However, the parameters in the models varied significantly, posing a significant challenge to describe microbial transport under different environmental conditions. A neural network (ANN) model was developed in this study to link the parameters in the model with the factors influencing microbial transport including the properties of microorganisms such as size and surface potentials, and the properties of porous media such as grain size and porosity, and flow conditions. Exhaustive search of literature renders 420 sets of experimental data of microbial transport, which were fitted using the microbial transport model to obtain model parameters. The model parameters, together with the factors influencing microbial transport, were then used to train an ANN model to search for their relationship. An ANN-based parameter relationship was derived and was then used to simulate microbial transport. The simulated results using the relationship roughly matched with the experimental data under different environmental conditions, indicating that a unified relationship was established between the parameters of the microbial transport model and the factors influencing microbial transport, and that microbial transport can be described using the microbial transport model with the ANN-based unified relationship for model parameters.

Leakage of metal oxide nanoparticles (MNPs) into marine environments is inevitable with the increasing use of MNPs. However, little is known about the effects of these lately emerged MNPs on the bioaccumulation and toxicity of pre-existing contaminants in marine biota. The current study therefore investigated the effects of two common MNPs, CuO nanoparticles (nCuO) and Fe3O4 nanoparticles (nFe3O4), on bioaccumulation and toxicity of arsenic (As) in green mussel Perna viridis. Newly introduced MNPs remarkably promoted the accumulation of As and disrupted the As distribution in mussels because of the strong adsorption of As onto MNPs. Moreover, MNPs enhanced the toxicity of As by disturbing osmoregulation in mussels, which could be supported by decreased activity of Na+-K+-ATPase and average weight loss of mussels after MNPs exposure. In addition, the enhanced toxicity of As in mussels might be due to that MNPs reduced the biotransformation efficiency of more toxic inorganic As to less toxic organic As, showing an inhibitory effect on As detoxifying process of mussels. This could be further demonstrated by the overproduction of reactive oxygen species (ROS), as implied by the rise in quantities of superoxide dismutase (SOD) and lipid peroxidation (LPO), and subsequently restraining the glutathione-S-transferases (GST) activity and glutathione (GSH) content in mussels. Taken together, this study elucidated that MNPs may elevate As bioaccumulation and limit As biotransformation in mussels, which would result in an enhanced ecotoxicity of As towards marine organisms.

Bacterium Shewanella oneidensis strain (MR1), a facultative microorganism that plays critical role in contaminant transformation and degradation, was used as an example to decipher the transport and retention of microorganisms in water-saturated porous media with different grain-surface properties and under different ionic compositions (i.e. Na+, Ca2+, and Mg2+). Dolomite and quartz sands, which contained different surface charge properties, were used as the representative minerals. Dolomite was selected because its surface charges are significantly affected by solution composition. The mobility of MR1 in the dolomite column was lower than that in the quartz column, because the lower energy barrier between MR1 and dolomite than that between MR1 and quartz, resulting in the larger retention of MR1 in the dolomite column. The breakthrough curves were well simulated by the two sites kinetic model with HYDRUS-1D. The maximum concentration of attached bacteria (Smax) were positively correlated to the ionic strength regardless of mineral types. The values of Smax were about 1.1–4.0 times larger in the MR1-dolomite system than that in the MR1-quartz system under different ionic strength conditions. The retention of the MR1 on dolomite surfaces in the presence of divalent cations Ca2+ is significantly higher than that on quartz surfaces primarily due to the larger electrostatic attraction energy between the MR1 and dolomite grains. The findings demonstrate that the porous media with the lower negative charge has the higher capacity for the retention and deposition of MR1, potentially affecting the transport of MR1 and other bacteria in the subsurface.

In lotic ecosystems highly susceptible to anthropogenic activities, the influences of environmental variables on microbial communities and their functions remain poorly understood, despite our rapidly increasing sequencing ability. In this study, we profiled the microbial communities in the hyporheic sediments of a watershed undergoing intensive anthropogenic activities via next-generation sequencing of 16S rRNA V4–V5 hypervariable regions on Illumina MiSeq platform. Tidal impacts on microbial communities were investigated via co-occurrence networks. In addition, the influences of physicochemical variables including salinity, and the concentrations of nutrients, organic matter and heavy metals on the microbial communities were explored via canonical correspondence analyses. The sediment samples were collected from 19 sites covering the whole main river stem of the target watershed (n = 19; Maozhou river watershed, Shenzhen, China). The samples were sub-divided in the field for microbiological analyses and measurements of physicochemical variables. The results indicated that core microbiome was associated with archaea methanogens and bacteria members from Proteobacteria, Chloroflexi, Bacteroidetes, Acidobacteria, Synergistetes and Firmicutes, among which, gram-negative and anaerobic bacteria genera contributing to the cycling of carbon, nitrogen and sulfur were predominant. Site-specific microbiomes were revealed that may serve as indicators of local environmental conditions (e.g., members affiliated to Oceanospirillales were abundant at sites with salt intrusion). Distinct microbial co-occurrence networks were identified for non-tidal, inter-tidal and tidal sites. Major environmental factors influencing microbial community composition included the concentrations of nitrate and bicarbonate in river water, pore water concentrations of sulfate, dissolved organic carbon and electrical conductivity, as well as manganese concentrations associated with the solid sediment. Collectively, the results of this study provide fundamental insights into the influence of environmental perturbations on microbial community composition in a lotic system, which may aid in the design of effective remediation and/or restoration strategies in the target watershed and beyond.

Wastewater reclamation now represents an effective measure for sustainable water resource management in arid regions, however wastewater components (organic micropollutants) may potentially impact local ecological and/or human health. Previous studies have shown that sodium bentonite/natural clay (BC) mixes may be used to effectively reduce riverbed infiltration in regions characterised by excessively high hydraulic conductivity. Accordingly, the current study sought to investigate the contaminant removal efficiency (Re) of several BC mass ratios in simulated dry riverbeds. Results indicate that the measured Re of NH4 +-N, CODcr and BOD5 increased in concurrence with an increasing sodium bentonite ratio, up to a maximum Re of 97.4% (NH4 +-N), 55.2% (CODcr), and 51.5% (BOD5). The primary contaminant removal site was shown to be the infiltration-reducing (BC) layer, accounting for approximately 40%, 60%, and 70% of NH4 +-N, CODcr and BOD5 removal, respectively. Conversely, the removal efficiency of NO3-N was found to be low (

Natural organic matter (NOM) can influence the toxicity and speciation of chromium (Cr) in subsurface through redox reactions and complexation. Under anoxic conditions, NOM can be reduced by microorganisms or geochemical reductants, and the reduced NOM (NOMred) represents a large reservoir of organic matter observed in anoxic sediments and water. While the current body of work has established the kinetic of Cr(VI) reduction by oxidized NOM (NOMox) under oxic conditions, much less is known about the rates and mechanisms of Cr(VI) reduction triggered by NOMred under anoxic conditions and the colloidal properties of the reaction products. This study provided new information regarding the NOMred-mediated Cr(VI) reduction and colloidal stability of reduced Cr(III) particles over a wide range of environmentally relevant anoxic conditions. We show that under dark anoxic conditions reduced humic acid (HAred) moieties (e.g., quinone) can quickly reduce Cr(VI) to Cr(III), and the reduced Cr(III) can subsequently complex with carboxyl groups of HA leading to the formation of stable HA-Cr(III) colloids. Rates of Cr(VI) reduction by HAred are 3–4 orders of magnitude higher than those by oxidized HA (HAox) due primarily to the higher reducing capacity of HAred. The stable HA-Cr(III) colloids are formed across a range of HA concentrations (8–150 mg C/L) and pH conditions (6–10) with hydrodynamic diameter in the range of 210–240 nm. Aberration-corrected scanning transmission electron microscopy (Cs-STEM) and X-ray photoelectron spectroscopy (XPS) confirmed that the particles are composed of HA-Cr(III). The high colloidal stability of HA-Cr(III) particles could be attributed to the enhanced electrosteric stabilization effect from free and adsorbed HA, which decreased particle aggregation. However, the presence of divalent cations (Ca2+ and Mg2+) promoted particle aggregation at pH 6. These new findings are valuable for our fundamental understanding of the fate and transport of Cr in organic-rich anoxic environments, which also have substantial implications for the development and optimization of subsurface Cr sequestration technology.

Attachment is an important strategy for microorganisms to survive, grow, and perform biogeochemical functions in soil and groundwater systems. This study investigated the effect of flow-interruption (FI) that is common in subsurface environments on bacterial attachment/detachment using a metal-reducing bacterium Shewanella oneidensis strain (MR1) as an example. Column experiments and one dimensional bacterial transport models were performed by varying flow interruption duration, fluid ionic strength, and solid grain surface electrostatic properties with a goal to understand the effect of FI on bacterial attachment/detachment. The results indicated that MR1 generally behaved as colloidal particles in transport and attachment/detachment under continuous flow conditions. However, the FI events induced a significant release of MR1 in both injection and elution phases, showing a peak MR1 concentration, which was higher than that in the injecting solution, immediately after the FI events. The peak MR1 concentrations were higher in systems with lower adhesive forces between bacteria and solid grains, a lower attachment site capacity in porous media, and a longer FI duration. The diffusive release of the previously attached bacteria during the FI events and the momentum force when flow re-started immediately after the FI events were likely the mechanisms leading to bursting release of bacteria with the release concentrations higher than that in the influent solutions. The results have important implication for understanding bacterial migration and attachment, and their subsequent functions, especially in dynamic hydraulic environments such as in hyporheic zones or in soils subject to dynamic changes in infiltration rates under for example extreme precipitation and drought conditions.

This is an Accepted Manuscript of an article published by Taylor & Francis in Soil Science and Plant Nutrition on 02 Feb 2017, available online: http://www.tandfonline.com/10.1080/00380768.2016.1277435., Behavior of radioactive strontium (Sr2+) in contaminated soils is an important issue in relation to nuclear power plant accidents. The Sr2+adsorption on kaolinite and its migration in a kaolinite soil were investigated because toxic effects of radioactive Sr2+have been found to be very severe for living organisms at low Sr2+concentrations. Adsorption isotherms of Sr2+on kaolinite at different salt (NaCl) concentration and pH were obtained by the batch method. The calculated distribution coefficients (KD) ranged between 600 and 40,000 L kg−1, which showed a strong preference for the adsorbed phase. The results were used to evaluate the ratio (r) of penetration length of Sr2+relative to that of water in a model kaolinite soil. When the Sr2+solution was percolated constantly into the kaolinite soil, the penetration ofSr2+was delayed strongly at low Sr2+concentration due to adsorption. The Sr2+penetration length was only 0.001–0.056 of the water penetration length at pH 6.5 (0.1–10 mmol L−1NaCl). At pH 4.1 (1 mmol L−1NaCl) the effect was about 17 times less than at pH 6.5 (1 mmol L−1NaCl). Under all conditions, the Sr2+penetration increased when the Sr2+concentration increased due to the KD decrease. The Sr2+isothermscould be fitted well to the Langmuir adsorption equation, which indicates that only one site type is involved in the Sr2+adsorption.

Potassium (K) is an important nutrient for agricultural crop growth. Adsorption of K in soil involves fertilizer optima for enhancing crop productivity and efficient nutrient management. Adsorption is often necessary to predict K transport and losses, such as solid/liquid distribution in soil, plant uptake, and transportation with water and suspended sediments. Based on the Soil and Water Assessment Tool (SWAT), the SWAT-K model has been developed to quantify daily K losses and budget at watershed scale. In this study, Langmuir and Freundlich adsorption equations were both applied and compared in the SWAT-K model to predict K adsorption in the soil and K losses in the volcanic Shibetsu River Watershed (672 km2, Hokkaido, Japan). Both the Langmuir and Freundlich adsorption equations well fitted the solid/liquid distribution of K in soil. The Freundlich and Langmuir equations showed similar performances to fit the measured data of K sorbed to soil (R2 = 0.91 for both cases) and Freundlich equation showed slightly better performances of dissolved K load in stream than Langmuir equation (Nash-Sutcliffe efficiency coefficient (ENS) = 0.66 and 0.60, respectively). Overall, Langmuir and Freundlich equations predicted similar K budgets, including soil K surplus with a difference of 1.2%. The uncertainty related to the choice of the adsorption equation is negligible. Hence, both Langmuir and Freundlich adsorption equations are recommended to predict the K adsorption in soil and in-stream K load when using the SWAT-K model in watershed similar to the study case. Their applicability deserve to be tested in other agricultural watersheds characterized by different soils.

Using reclaimed water has become one of the most effective ways to solve the problem of urban water shortage. Using mixtures of sodium bentonite and clay to reduce infiltration is an important safeguard measure to meet the need of groundwater recharge and water quality safety. The microscopic structure of sodium bentonite was studied with environmental scanning electron microscopy. The effect of different mix ratios of sodium bentonite and clay on the performance of reducing infiltration was studied with constant head infiltration experiments and adsorption of ammonium and phosphate with the batch method. The results showed that the dry particles of sodium bentonite had lamellar and compact structure, after absorbing water, and both the number and size of pores gradually reduced to become uniform distributions. With the increase of bentonite mix ratio (10–20 % of the total dry weight), the infiltration coefficient of the mixed materials decreased exponentially (R2 = 0.95). Linear, Freundlich, and Langmuir equations could be used to describe adsorption of N/P on the mixed materials. There were significant correlations between adsorption parameters (Sm and MBC) and bentonite mix ratio. The effect of removing ammonium with mixtures was better than that of phosphate. Considering synthetically the capability of reducing infiltration and decontamination, a mixture of 19 % bentonite and 81 % clay was a suitable model in the Yongding River in Beijing plain segment.

Adsorption and retardation of Sr2+ by four clays were investigated, which were evaluated by using the distribution coefficient (K D ) and average penetration length ratio of Sr2+ to water (r). K D values for Sr2+ among the four clay minerals were in the order: kaolinite

Biofilms, abundantly attached on the surfaces of multiple media (such as pebbles and aquatic plants) in rivers or lakes reusing reclaimed water (RW), are of great significance to contaminants’ self-purification of water bodies. In this paper, the nitrogen and phosphate adsorption characteristics of such biofilms were studied by the batch method, using biofilms cultivated under an outdoor simulative process. Two types of RW treated by anaerobic-anoxic-oxic process (A2/O) and cyclic activated sludge technology (CASS), and surface water (NW) were chosen as the experimental water bodies. And the glasses of surface roughness of 0.1, 1.0, and 10 μm, respectively, were used as the substrates, where the biofilms adhere to them. The results indicated that the isothermal adsorption of biofilms for ammonia nitrogen and phosphates was proved to conform to the Langmuir and the Freundlich equation, whereas the adsorption capacity was significantly lower than that of soils and sediments limited by the pore structure and surface area. There were also significant differences between the adsorption behaviors. The distribution coefficients were ranked as K dCASS > K dNW > K dA 2 /O, and the maximum adsorption capacities (S m), under these conditions were ranked as S mA 2 /O > S mNW > S mCASS, while other parameters did not change regularly. Extracellular polymers ( $$R^{ 2}_{\text{N}}$$ = 0.95**, $$R^{ 2}_{\text{p}}$$ = 0.84**), iron oxides ( $$R^{ 2}_{\text{N}}$$ = 0.86**, $$R^{ 2}_{\text{p}}$$ = 0.68*), and aluminum oxides ( $$R^{ 2}_{\text{N}}$$ = 0.95**, $$R^{ 2}_{\text{p}}$$ = 0.81**) in the biofilms had a significant impact on the S m for ammonia and phosphates. The roughness of media surfaces also had a considerable influence on the S m, which was in the order of S m10μm > S m0.1μm > S m1.0μm, whereas other parameters did not change regularly. The research aimed to provide theory reference for in situ decontamination of RW in rivers or lakes.

Adsorptions of Dimethyl Phthalate (DMP) on three sediments in both reclaimed and ultrapure water were studied using the batch technique and the effects of reclaimed water on it were clarified. The data were interpreted by using Freundlich and Dubinin-Radushkviech models. The values of 1/n were among 0.207 to 0.766, showing the presence of multiple adsorption sites on sediments. Compared with the ultrapure water as the background solution, the adsorption capacities of sediments for DMP were reduced in case of reclaimed water due to the competition of substances in reclaimed water. The mean adsorption energy, E, is smaller in the reclaimed water than that in ultrapure water.

Hyporheic zone (HZ) sediments in river systems are often contaminated with heavy metals as a legacy of natural processes and anthropogenic activities. The geochemical behaviors of heavy metals in the HZ sediments at the laboratory scale have been extensively studied. However, the watershed-scale distributions of heavy metals in the HZ sediments and the processes controlling their distributions have not been well studied. Here, we report a watershed-scale study of heavy metals (i.e., Cr, Ni, Cu, Zn, Cd, and Pb) distributions in the HZ of the Maozhou River watershed, a heavily polluted area within the Pearl River Delta, southern China. Statistical analysis revealed that the spatial distribution of studied heavy metal concentrations was highly correlated with that of the sediment-associated sulfide at the watershed-scale. Metal extraction analysis and double-spherical aberration-corrected scanning transmission electron microscope imaging (Cs-STEM) further confirmed the strong association of heavy metals with sulfur. These observations demonstrated that the formation of metals-sulfide precipitates was the key process controlling the watershed-scale distributions of heavy metals (especially for Cr, Ni and Zn) in the HZ sediments. Additionally, high permeability of the HZ sediments may prevent Ni, Zn, Cd and Pb accumulation in sediments. Specially, Cu distribution was mainly affected by organic-Cu complexation. In the estuary area, salinity input likely affected the distributions of Ni, Zn and Cd through cation exchange processes. The findings improved our understanding of the distributions of heavy metals and the processes controlling their distributions at the watershed-scale, and have implications for remediating and managing contaminated HZ sediments.

Reusing reclaimed water for the ecological water has become one of the effective ways to alleviate the water crisis in the rivers and lakes, while its impact on the river and lake ecosystems has become the focus of public attention. The microorganism is one of the most direct and effective monitoring objects, which is generally present in the form of biofilm. Therefore, three kinds of water with different water quality were chosen, which included reclaimed water treated with anaerobic–anoxic–oxic (A2/O) and cyclic activated sludge system process, and surface water, respectively. Glass plates with different roughness (0.1, 1.0 and 10 μm) were used as attaching matrix. Biofilms were cultured with the help of outdoor simulation environment; and the dynamic variation of the biofilm dry weight as well as inorganic and organic components were analyzed. The results showed that the content for dry weight, iron oxide, extracellular polymeric substances (EPS) and chlorophyll a of biofilms attached on multi-media surface in three kinds of water body increased sequentially during the rapid growth period, while the activity of phosphatase fluctuated. Biofilm dry weight and chlorophyll a variation can be described double-constant rate equation (R 2 is over 0.90 and 0.91, respectively), while the iron oxide and EPS content could make use of the parabolic diffusion equation (R 2 is over 0.88 and 0.87, respectively). For the surface of the medium with different roughness, dry weight of the different biofilms with roughness 1.0 μm has the largest content, up to 1.39 mg cm−2. With regard to iron oxide, the content differences are little with different roughness and the maximum content is up to 0.36 μg cm−2, while no significant difference existed between the different water bodies. The contents of EPS, chlorophyll a and phosphatase activity in reclaimed water are higher than that in the surface water, and both of them have the highest content with the roughness 1.0 μm medium surface. Testing phospholipid fatty acids showed that the dominant bacteria are i15: 0, bacteria under two processes of reclaimed water in biofilms were, respectively, higher by 3.7 and 3.5 % than the surface water. Biofilm EPS and chlorophyll a concentration was positively correlated with pH, total phosphorus, COD and Mg2+ concentration in the reclaimed water, and was negatively correlated with NH4+, while the phosphatase activity showed no correlation with water quality indicators. This research aimed to provide a theoretical basis and technical support for health assessment of reclaimed water as the ecological water ecosystem for urban rivers and lakes.

The nitrogen and phosphate were regarded as the target pollutants in this paper to study the balance of adsorption / desorption to nitrogen and phosphate, the adsorption dynamic characteristics under the action of four kinds of urban rivers and lakes sediments in Beijing as well as the impact of DOM in reclaimed water to absorb nitrogen and phosphate. Results show that: the processes of sorption of nitrogen and phosphate in the four sediments could be described by the Linear and Freundlich models, while the adsorption-desorption goes with hysteresis effect. The adsorption of nitrogen and phosphate were inhibited by DOM in reclaimed water, with an adsorption coefficient Kddecreasing by 0.04% -56.88%, reaching a significant level (confidence level α = 0.05);And DOM increased the nonlinear parameter 1/n, up to 2.20 times at most, resulting in a lower adsorption stable.

There are many reports of NO3− violating safety standards in the neighboring areas of concentrated animal feeding operations (CAFOs), which have become the bottleneck of the CAFOs development. The high concentration of ammonium nitrogen (NH4+-N), which transforms into nitrate nitrogen (NO3−-N) through nitrification, and then leaches into the groundwater, is a potential threat to the environment. Adsorption and desorption characteristics of ammonium can reduce the amount of NH4+-N in soils, which effectively prevents or slows down the nitrate leaching. Researches on the adsorption and desorption of ammonium mainly focus on the simple NH4+ solution. Researches on the adsorption and desorption from hogpen wastewater are few, which is a complex system coexisting with many ions. In this paper, ammonium was selected as the object of pollutant, a batch of equilibration experiments was conducted to evaluate the adsorption–desorption and its kinetics in eight loams, typically found in Northern China, irrigated with original wastewater (OW) and reclaimed wastewater (RW) from intensive hogpen and a simple one consisting of clean water (CW). This study showed that the Freundlich and Langmuir model described the ammonium adsorption properties very well in multi-ion coexistensive system of hogpen wastewater; the ammonium adsorbed amount in the corresponding matrices followed by OW < RW < CW tendency, although the adsorption model parameters had great diversity. The adsorbed amount increased as the adsorption time went on and then approached to a stable state. CW had the shortest reaction time to reach equilibrium, whereas OW had the longest. The normal adsorption kinetics equation could not depict the adsorption behavior of loams but characterized by the ExpAssoc equation well. The study could provide references for the wastewater treatment and recycling, and rural water pollution controlling.