Water-sediment System Research Articles

Influence of chemical charge on the fate of organic chemicals in sediment particle size fractions

In order to investigate the influence of differently sized particle fractions on the fate of ionic chemicals in water-sediment systems, we performed simulation studies following OECD guideline 308. We used 14C-labelled anionic (4-n-dodecylbenzenesulfonic acid sodium salt, ‘14C-DS-’), cationic (4-n-dodecylbenzyltrimethyl ammonium chloride, ‘14C-DA+‘) and non-ionic (4-n-dodecylphenol, ‘14C-DP’) organic chemicals. The sediment was subjected to particle size fractionation. For each particle fraction and test compound, water-sediment systems were prepared and incubated for 14 days. Across all particle fractions, higher amounts of applied radioactivity (AR) of 14C-DS- (in sand 60.1%, in silt 45.1%, in clay 57.0%) and of 14C-DP (sand: 31.8%, silt: 24.4%, clay: 29.2%) were mineralised compared to 14C-DA+ (sand: 5.1% AR, silt: 3.5% AR, clay: 2.4% AR). The highest bioavailability was observed for 14C-DS- followed by 14C-DP and 14C-DA+ across all particle fractions. Formation of non-extractable residues (NER) of 14C-DS- did not substantially differ between the particle fractions, whereas NER formation of 14C-DA+ was higher in the clay fraction (24.3% AR) than in silt (15.9% AR) and sand (8.4% AR). The same trend was observed for 14C-DP. We showed that differently sized particle fractions have an influence on the fate of ionic chemicals in water-sediment systems and conclude that this should be considered when simulation studies in soils and sediments with different textural compositions are performed. Since a positive charge of organic chemicals tends to form higher portions of NER in the clay fraction of sediments, these NER should be further investigated in terms of their nature and types of binding.

Radiocesium distribution and mid-term dynamics in the ponds of the Fukushima Dai-ichi nuclear power plant exclusion zone in 2015–2019

This study analyzes the 137Cs behavior in the ponds of Okuma Town from 2015 to 2019 in the Fukushima Dai-ichi nuclear power plant (FDNPP) exclusion zone. A decline in both particulate and dissolved 137Cs activity concentrations was revealed. The decline rate constants for the particulate 137Cs activity concentration were found to be higher than for the dissolved 137Cs activity concentration. In terms of seasonality the dissolved 137Cs concentrations were higher from June to October, depending on the specific pond and year, most likely due to temperature dependence of 137Cs desorption from frayed edge sites of micaceous clay minerals. The apparent Kd(137Cs) in the studied ponds, in absolute value, appeared to be much higher than that for closed and semi-closed lakes of the Chernobyl contaminated area; however, these were comparable to the values characteristic of the rivers and reservoirs of the FDNPP contaminated area. The apparent Kd(137Cs) in the suspended sediment–water system was observed to decrease over time. It was hypothesized that this trend was associated with the decomposition of glassy hot particles. Relying on the theory of selective sorption and fixation, the exchangeable radiocesium interception potential, RIPex(K) was estimated using data on 137Cs speciation in the surface bottom-sediment layer and its distribution in the sediment–water system. For the studied ponds, RIPex(K) was on the average 2050 mEq/kg, which is within the range of values measured in laboratory studies reported in the literature.

Microbial activity and metamitron degrading microbial communities differ between soil and water-sediment systems

The herbicide metamitron is frequently detected in the environment, and its degradation in soil differs from that in aquatic sediments. In this study, we applied 13C6-metamitron to investigate the differences in microbial activity, metamitron mineralization and metamitron degrading microbial communities between soil and water-sediment systems. Metamitron increased soil respiration, whereas it suppressed respiration in the water-sediment system as compared to controls. Metamitron was mineralized two-fold faster in soil than in the water-sediment. Incorporation of 13C from 13C6-metamitron into Phospholipid fatty acids (PLFAs) was higher in soil than in sediment, suggesting higher activity of metamitron-degrading microorganisms in soil. During the accelerated mineralization of metamitron, biomarkers for Gram-negative, Gram-positive bacteria and actinobacteria dominated within the 13C-PLFAs in soil. Gram-negative bacteria dominated among the metamitron degraders in sediment throughout the incubation period. Actinobacteria, and actinobacteria and fungi were the main consumers of necromass of primary degraders in soil and water-sediment, respectively. This study clearly showed that microbial groups involved in metamitron degradation depend on the system (soil vs. water-sediment) and on time. It also indicated that the turnover of organic chemicals in complex environments is driven by different groups of synthropic degraders (primary degraders and necromass degraders) rather than by a single degrader.

Improved Short-Term Microbial Degradation in Circulating Water Reducing High Stagnant Atrazine Concentrations in Subsurface Sediments

The triazine herbicide atrazine easily leaches with water through soil layers into groundwater, where it is persistent. Its behavior during short-term transport is poorly understood, and there is no in situ remediation method for it. The aim of this study was to investigate whether water circulation, or circulation combined with bioaugmentation (Pseudomonas sp. ADP, or four isolates from atrazine-contaminated sediments) alone or with biostimulation (Na-citrate), could enhance atrazine dissipation in subsurface sediment–water systems. Atrazine concentrations (100 mg L−1) in the liquid phase of sediment slurries and in the circulating water of sediment columns were followed for 10 days. Atrazine was rapidly degraded to 53–64 mg L−1 in the slurries, and further to 10–18 mg L−1 in the circulating water, by the inherent microbes of sediments collected from 13.6 m in an atrazine-contaminated aquifer. Bioaugmentation without or with biostimulation had minor effects on atrazine degradation. The microbial number simultaneously increased in the slurries from 1.0 × 103 to 0.8–1.0 × 108 cfu mL−1, and in the circulating water from 0.1–1.0 × 102 to 0.24–8.8 × 104 cfu mL−1. In sediments without added atrazine, the cultivable microbial numbers remained low at 0.82–8.0 × 104 cfu mL−1 in the slurries, and at 0.1–2.8 × 103 cfu mL−1 in the circulating water. The cultivated microorganisms belonged to the nine genera Acinetobacter, Burkholderia, Methylobacterium, Pseudomonas, Rhodococcus, Sphingomonas, Streptomyces, Variovorax and Williamsia; i.e., biodiversity was low. Water flow through the sediments released adsorbed and complex-bound atrazine for microbial degradation, though the residual concentration of 10–64 mg L−1 was high and could contaminate large groundwater volumes from a point source, e.g., during heavy rain or flooding.

Spatial distribution of polycyclic aromatic hydrocarbons in the water–sediment system near chemical industry parks in the Yangtze River Delta, China

The Yangtze River Delta (YRD) is one of the most populated and economically prosperous regions in China and contains numerous chemical industry parks. To understand the distribution and sources of polycyclic aromatic hydrocarbons (PAHs), surface water and sediment samples were collected from areas around the industrial parks. The total concentrations of 19 PAHs in water and sediment were 32.98–286 ng L−1 and 15.14–5355 ng g−1, respectively. The highest PAH concentrations in water and sediment were found in samples from Wuxi city, which were dominated by high molecular weight (HMW) PAHs, and strongly influenced by fine chemical parks. HMW compounds dominated in the sediment with PAHs containing four and five rings accounting for 61% of the sedimentary ΣPAHs, PAHs in water were dominated by low molecular weight (LMW) compounds (PAHs with two and three rings represented >68% of ΣPAHs). The results of isomeric ratio analysis and principal component analysis with multiple linear regression indicated that the PAH concentrations in water and sediment near the YRD chemical parks are strongly influenced by industrial emissions. The fugacity fraction approach was applied to explain the trend for water–sediment exchange of 16 priority PAHs, which showed that net fluxes for most were from the sediment into water. The results indicated that the LMW PAHs were in a non-steady state in the sediment–water system. An ecological risk assessment showed that most sites were low to medium risk, but one site was high risk.

Dissipation of Herbicide Methiozolin and Its Metabolites in Aerobic Sediment–Water Systems

Methiozolin is a novel herbicide for controlling annual bluegrass. After applying 14C labelled methiozolin in two sediment (clay loam and sand)-water systems under aerobic conditions, its distribution, half-life, and metabolites within 300days were investigated. The mass balance ranged within 92.0%-104.4% of applied radioactivity (AR). Radioactivity in the water declined sharply from 94.4% to 0.5% AR, while in the sediment it increased to 83.9% AR at 14days before declining to 9.1% AR. The volatiles were minimal (< 0.5% AR), and the evolved labelled CO2 accounted for up to ~ 33.4% AR. From Radio-HPLC analysis, labelled methiozolin in water decreased from 108.9% to 0% AR, while a maximum of 15.1% AR remained in the sediment at the end. Eight metabolites were detected, all at minor levels and accounting for < 5.5% AR. The half-life of labelled methiozolin in the total sediment-water systems were 50.7 and 38.7days for clay loam and sand, respectively.

Using sediment resuspension to immobilize sedimentary phosphorus.

The response of the transformation of internal phosphorus (P) to resuspended sediment was investigated in the sediment-water system under different disturbance intensity. The sediments and overlying water were collected from Taihu Lake, a typical shallow lake. The concentrations of particulate P (PP) and dissolved inorganic P (DIP) in the water phase and algal available P (AAP) and P fractions in the sediments and suspended particle characteristics were evaluated in laboratory-simulated experiments. The results show that dissolved oxygen (DO) in the overlying water increased continuously and pH decreased slightly under sediment resuspension. The concentration of ammonia nitrogen (NH4+-N) showed a distinct decline, indicating that sediment resuspension promotes the penetration of DO into the sediments. It was also favor of the formation of metal oxides and hydroxides, inducing soluble amorphous metal compounds oxidized to insoluble crystalline metal compounds under disturbance condition. This resulted in the increase of refractory P in sediment compared with the static conditions. Sediment resuspension is beneficial to long-term P retention. This can be confirmed by the increase of maximum P adsorption amount (Qmax) and the decrease of the degree of P saturation (DPS) and equilibrium P concentration (EPC0). This is the main explanation of DIP decrease in the overlying water. It is indicating that sediment resuspension not only improves the redox environment in the sediment-water system but also enhances P retention capacity.

Legacy and emerging per- and polyfluoroalkyl substances (PFASs) in multi-media around a landfill in China: Implications for the usage of PFASs alternatives

To date, per- and polyfluoroalkyl substances (PFASs) in environmental media surrounding landfills have not attracted much attention. In this study, six legacy PFASs, six short-chain analogues and five emerging alternatives were investigated in groundwater, surface water and sediment samples taken in the vicinity of a valley-type landfill, which had been in operation for over 20 years. Total PFAS concentrations of 110–236 ng/L, 17.3–163 ng/L and 7.91–164 ng/g dw were detected in the surface water, groundwater and sediment samples, respectively. Overall, perfluorooctanoic acid (PFOA) was the dominant PFAS in surface water, but elevated concentrations of perfluorobutanoic acid (PFBA) and perfluoropentanoic acid (PFPeA) were detected in the surface water samples taken adjacent to the landfill, suggesting that the landfill contributed to these compounds. PFBA was the dominant PFAS in the groundwater and sediments. The concentrations of long-chain perfluoroalkyl carboxylic acids (PFCAs) (C8–C12) in the sediment samples correlated significantly with the TOC, Al2O3 and Fe2O3 contents. The partitioning behaviors of PFCAs in the water-sediment system varied depending on the CF2 moiety units. For the long-chain PFCAs, positive correlations between the average LogKd and the number of CF2 moieties were found to be statistically significant, whereas negative correlations were observed for the short-chain PFCAs (C4–C7). The ratios of short-chain analogues and emerging alternatives versus their respective legacy PFOA and perfluorooctane sulfonate (PFOS) in surface water suggested an increasing trend of short-chain analogues, such as PFBA. The potential health risks of PFOS and PFOA, determined by calculating the estimated daily intake (EDI), were found to be negligible via the drinking groundwater exposure pathway, but more comprehensive studies on the human health risks of PFASs from landfills are essential.

Kinetic study on the sorption and degradation of antibiotics in the estuarine water: an evaluation based on single and multiple reactions.

It is important to study the fate and transport of antibiotics in aquatic environments to reveal their pollution status. The premise behind fate and transport studies is to evaluate the reaction processes of the target antibiotics. However, available research on the environmental behaviors of antibiotics in certain natural waters, such as estuarine water, is scarce. In this study, single reactions such as sorption, biodegradation, and photolysis and multiple degradation reactions of sulfamethoxazole (SMX), trimethoprim (TMP), and ciprofloxacin (CIP) in the estuarine water were studied. The sorption rates of the target antibiotics in the estuarine water-sediment system were very fast, and the sorption amounts varied among sediments and antibiotics. Hydrolysis did not contribute to the degradation of the target antibiotics. Biodegradation had a low contribution to the degradation of the target antibiotics in the estuarine water. In comparison, photolysis was the dominant degradation process for SMX, TMP, and CIP. The rates of photolysis of the tested antibiotics in the estuarine water were greater than those in pure water; thereby, indicating photolysis of these antibiotics was more prone to occur in the estuarine water. In the multiple degradation experiments, it was found that there may be synergistic effects between the single degradation processes. Thus, the aqueous concentrations of antibiotics decreased rapidly by sorption after entering the estuarine water and then decreased relatively slowly by photolysis and biodegradation. This study provides information for evaluating the environmental behaviors of antibiotics in estuarine environments.

Priming effect of autochthonous organic matter on enhanced degradation of 17α-ethynylestradiol in water-sediment system of one eutrophic lake

Climate change and increasing eutrophication are expected to increase the release of autochthonous organic matter (OM) to sediments, where most contaminants are transformed or mineralized in freshwater lakes. This study sought to evaluate how cyanobacteria- and macrophyte-derived OM (COM and MOM) affected the microbial attenuation of 17α-ethinylestradiol (EE2) in the sediment from eutrophic Lake Taihu in China. In two months of water-sediment microcosm experiments, the input of COM and MOM both promoted EE2 degradation more strongly than humic acids, and the degradation efficiency was significantly and positively correlated with the cometabolism of increasing organic carbon in sediments (P < 0.001). The enhanced degradation was explained by responses of indigenous bacterial community to OM amendment as a priming effect. The immediate breakdown of biodegradable components such as proteinaceous substances in COM and MOM remarkably augmented the metabolic activity of bacteria in terms of the stimulated activity of extracellular enzymes including fluorescein diacetate and dehydrogenase, as well as the elevated production of proteins and polysaccharides in extracellular polymeric substances. In the meantime, the bacterial community composition was reshaped toward a more eutrophic state, leading to the clear upregulation of metabolic function genes of organic carbon and xenobiotics. Correlation-based network analysis further determined the strong facilitative coordination between the community members and the compositional variability of OM in the cometabolism. These results suggest that cyanobacterial blooms-dominated zones are potential hotspot areas for steroid estrogen attenuation, a finding of significance for the control and management of complex pollution in freshwater lakes.

Long-term changes in water mineral concentrations and their influence on sediment water content in a shallow lake

During the last four decades, substantial changes have been observed not only in tripton concentrations but also in other limnological parameters in Lake Kasumigaura, a shallow eutrophic lake. A previous study reported that tripton concentration showed a positive correlation with sediment water content (WC) and a negative one with sediment ignition loss. To explain the changes in sediment WC, we conducted an analysis of the changes in mineral concentrations and sediment WC during 1979–2016 to determine their relationship. High mineral concentrations in water throughout the lake were observed in the latter half of the 1990s and higher WC in sediments followed with a time lag of a few years, resulting in significant correlations. The relationship between them was confirmed in laboratory experiments that indicated swelling of sediments (slowdown of sediment compaction) by the addition of NaCl into the water-sediment system. In contrast, significantly lower SS concentrations in overlying waters observed in higher mineral conditions were similar to previous studies. The significantly low annual precipitation during 1994–1997 probably caused high Na+ and Cl- concentrations in the lake waters in the latter half of the 1990s. The combined influence of sea-spray aerosol and evaporation was suspected to be the cause of high salt concentrations. The intrusion of salty water through the downstream gate and/or surrounding construction structures was another possibility.

Influence of Nutrient Pulse Input on Nitrogen and Phosphorus Concentrations and Algal Growth in the Sediment-Water System of Lake Taihu

Lake sediments not only act as a reservoir of nutrients, but are also a source of secondary pollution of nutrients for overlying water, which can buffer the variations in nutrients in overlying water and affect nutrient bioavailability and algal growth. In the current study, a simulation experiment was conducted using sediment cores collected in Meiliang Bay. Our aim was to elucidate the effect of nitrogen (N) and phosphorus (P) pulse input on variations in the water nutrient level and algal growth. We also clarified the migration and redistribution process of N and P between the sediment overlying water and algae. The results showed that the concentration of N in overlying water of the treatment group (with sediment) was much lower than that in controls (no sediment) when N was input at a pulse rate of 0.30 mg·(L·d)-1. The loss rate of N in the overlying water of the treatment group ranged from 0.144 mg·(L·d)-1 to 0.156 mg·(L·d)-1 and that in the control ranged from 0.021 mg·(L·d)-1to 0.039 mg·(L·d)-1. On the contrary, the denitrification rate of overlying water in the treatment group ranged from 40.793 mg·(m2·d)-1 to 44.193 mg·(m2·d)-1, accounting to 48%-52% of the external N loading. In contrast, the denitrification rate of overlying water in controls was from 0.021 mg·(L·d)-1to 0.039 mg·(L·d)-1, only accounting for 7%-13% of the external N loading. These results indicated that the sediment-water interface is the main site of denitrification in shallow lakes and plays an essential role in reducing N pollution in lakes. With respect to the pulse input of P at a rate of 0.015 mg·(L·d)-1, the majority of P (about 52%-58%) was imported into the sediment at a rate from 2.210 mg·(m2·d)-1to 2.422 mg·(m2·d)-1, and only a small proportion, approximately 23%-26%, was utilized by algae. The remaining P existed in overlying water in a dissolved state. These results implied that the sediment can buffer the external P input as an obvious "sink" effect of nutrients. Our results also showed that the sediment acts as a "source" of P when no external P was added. The release rate of P from the sediment to overlying water was from 0.310 mg·(m2·d)-1 to 0.468 mg·(m2·d)-1. In situ high-resolution analysis of ZrO-Chelex DGT showed that the DGT-P concentration in the interstitial water was much higher than that in the overlying water, and the concentration of DGT-P was significantly correlated with the concentration of DGT-Fe in interstitial water. These results indicate that changes in the redox potential may cause considerable release of internal phosphorus. In summary, our study showed that internal P in sediments can be released into the overlying water and support the growth of algae when the external nutrients are controlled. As a result, a delayed response was observed in the nutrient concentration in overlying water to external P reduction. Therefore, the dual control of N and P may have a better practical application to mitigate cyanobacteria blooms in shallow lakes.

Pollution characteristics, spatial variation, and potential risks of phthalate esters in the water–sediment system of the Yangtze River estuary and its adjacent East China Sea

Spatiotemporal variability in seawater, spatial variation in sediment, pollution characteristics, and risks related to 16 phthalate esters (PAEs) were investigated in the Yangtze River estuary and its adjacent East China Sea. The total concentrations of ΣPAEs in surface water were 0.588–17.7 μg L−1 in summer, 2.63–22.9 μg L−1 in winter, and 1.93–20.7 μg L−1 in spring, with average values of 2.05, 10.2, and 4.89 μg L−1, respectively. PAE concentrations exhibited notable seasonal variations with the highest value in winter and the lowest value in summer. The seasonal variation in PAE concentrations may be influenced by runoff and diluted water from the Yangtze River. The chemical composition of PAEs showed that di-n-butyl phthalate (DnBP), diisobutyl phthalate (DiBP), and di(2-ethylhexyl) phthalate (DEHP) had significantly higher (p < 0.05) concentrations than the other congeners and were the most abundant PAE species in sediment and seawater in all three seasons. In addition, DnBP and DiBP were the two main congeners in seawater, and DEHP concentrations were higher in sediment than in seawater. DEHP had higher potential risks to sensitive organisms in water environment than DnBP and DiBP, and DiBP and DnBP which presented high levels of risk in sedimentary environment. DMP and DEP in watery and sedimentary environments and DEHP in sedimentary environment showed no or low risks to sensitive organisms.

Developmental/reproductive effects and gene expression variations in Chironomus riparius after exposure to reclaimed water and its fortification with carbamazepine and triclosan

The potential benefits of reclaimed water (RW) uses for environmental enhancement and restoration could become adverse impacts if RW does not meet the quality criteria that ensure wildlife preservation. RW can contain complex mixtures of micropollutants that may accumulate in sediment after environmental uses and affect benthic fauna. Therefore, we designed this study to assess the effects of RW on a sediment insect species used mainly in ecotoxicology (Chironomus riparius). Whole organism effects and gene expression were measured in a water sediment system after spiking RW as overlying water, which was renewed 3 times during the test. Development rate, emergence rate and fecundity were monitored after the 21-day exposure. Endocrine-related genes (EcR, ERR, E75, Vtg), cellular stress genes (hsp70, hsc70, hsp24, hsp10) and biotransformation genes (gp93, GSTd3, GPx, cyp4g) were assessed in larvae after the 10-day exposure. The experimental design also included single or binary fortifications of both test medium and RW, obtained by adding two emerging pollutants: carbamazepine (100 μg/L CBZ) and triclosan (20 μg/L TCS). The chemical characterisation of RW showed that 20 of the 23 screened emerging pollutants fell within the detection limit, 10 exceeded 0.01 μg/L (including CBZ) and three exceeded 0.1 μg/L (hydrochlorothiazide, atenolol, ibuprofen). The analytical measures of sediment (day 21) and overlying water (days 7, 14 and 21) were taken to know the water-sediment distribution of CBZ and TCS added to fortifications. CBZ distributed mainly in overlying water (110–164 μg/L and 73–100 μg/kg), while TCS showed a higher affinity to sediment (2.8–5.1 μg/L and 36–55 μg/kg). RW had significant effects in molecular terms (Vtg, hsp70, hsc70), but had no significant effects on the whole organism. Nevertheless, the single RW fortifications impaired both the development rate and fecundity, while the binary RW fortification impaired only fecundity. The most marked increase in EcR expression was observed for the binary RW fortification. Hsps, GSTd3 and cyp4g showed a similar tendency to that observed for EcR and Vtg in the binary and single RW fortifications. The binary mixture (CBZ and TCS together) in RW was toxic, but not in the medium tests. Therefore, the major concern of RW uses is apparently related to the interactivity between this complex matrix and any other pollutants possibly present in the environment where RW is applied. Our results underscore the need for raising awareness about RW effects, which can be achieved by ecotoxicological testing.

Phosphorus transformation under the influence of aluminum, organic carbon, and dissolved oxygen at the water-sediment interface: A simulative study

The effects of sediment aluminum (Al), organic carbon (OC), and dissolved oxygen (DO) on phosphorus (P) transformation, at the water-sediment interface of a eutrophic constructed lake, were investigated via a series of simulative experiments. The above three factors had various influences on dissolved P concentration, water pH, water and surface sediment appearance, and P fractions. Additions of Al had the greatest effect on suppressing P release, and the water pH remained alkaline in the water-sediment system under various OC and DO conditions. No dissolution of the added Al was detected. 31P-NMR characterization suggested that OC addition did not promote biological P uptake to polyphosphates under oxic conditions. The simulation result on the added phytate indicated the absence of phytate in the original lake sediment. As compared to the reported natural lakes and wetland, the water-sediment system of the constructed lake responded differently to some simulative conditions. Since Al, OC, and DO can be controlled with engineering methods, the results of this study provide insights for the practical site restorations.

The influence of polyethylene microplastics on pesticide residue and degradation in the aquatic environment

Microplastics pollution has become a global concern in recent years. In this work, the potential influences of polyethylene (PE) microplastics on the residue, degradation and distribution behaviors of eight pesticides (epoxiconazole, tebuconazole, myclobutanil, azoxystrobin, simazine, terbuthylazine, atrazine and metolachlor) in the aquatic environment were investigated. The results showed that the presence of 2−50 g L−1 microplastics could decrease the pesticide residues in water. The adsorption isotherms were linear, indicating the process was dominated by partitioning into the bulk polymer. The desorption kinetics data implied the desorption process obeyed a pseudo-second-order kinetic model, with R2 above 0.99 in most cases. Aging treatment of microplastics had no significant effects on the interaction with the pesticides. The presence of PE microplastics could significantly prolong the degradation half-lives of pesticides in water, especially for those with moderate degradation half-lives and high log Kow values. Take terbuthylazine as an example, its half-life significantly increased from 31.8 days to 45.2 days in the presence of 10 g L–1 microplastics. Besides, PE microplastics had little impact on the behavior of the pesticides in the water-sediment system. The findings of this study indicated that PE could adsorb pesticides through partitioning, thus influencing the persistence of the pesticides in water.

The Connection between a Suspended Sediments and Reservoir Siltation: Empirical Analysis in the Maziarnia Reservoir, Poland

This paper presents research on the influence of suspended sediments on selected aspects of a reservoir’s functioning. As the amount of sediment suspended in water (SS) there was found to correlate significantly with sedimentation rate (Us), it was possible to develop a function allowing the rate of accumulation of sediments to be predicted by reference to known amounts of suspended sediment. The latter factor was also shown to correlate significantly with the content of organic matter in suspension (OMSS), in sediment captured in a sediment trap (OMS), and of bottom sediment (OMSB). Analysis of amounts of suspended sediment can provide for estimates of total loads of organic pollutants deposited in the sediments of a reservoir. A further significant correlation with SS was noted for the concentration of total phosphorus in water (TPW), confirming the importance of internal production where the circulation of this biogenic substance in a reservoir ecosystem is concerned. Analysis of stable carbon isotopes in turn showed that entrapped sediments were depleted of—or enriched in—13C, in line with whether concentrations of total P in those sediments (TPS) were at their highest or lowest levels. This dependent relationship may thus be of key importance in assessing sources of phosphorus, as well as in forecasting concentrations present in reservoir sediments. The results obtained make it clear that sediments suspended in the water of a reservoir unify phenomena and processes ongoing there, between elements of the water-sediment system.

Temporal dynamics of antibiotic resistant genes and their association with the bacterial community in a water-sediment mesocosm under selection by 14 antibiotics

Antibiotics in aquatic environments at high concentrations and sub-inhibitory concentrations potentially select for the evolution of antibiotic resistant genes (ARGs), posing a potential risk to aquatic ecological safety. Our knowledge of the temporal and successive dynamics of ARGs and bacterial community under the selective pressure of antibiotics in natural water-sediment system was limited. This study used a 120-d operating hydrodynamic mesocosm to explore the temporal dynamics of ARGs in water-sediment systems, and the main selective mechanisms following the attenuation and transport of 14 commonly used antibiotics. Under the selective pressures by antibiotics, ARGs propagated transiently, and persisted after antibiotic removal; the bacterial community structures likewise changed. Mantel test and network analysis indicated that ARGs significantly correlated with the bacterial community in the water and surface sediments. Structural equation model (SEM) further revealed that the evolution of ARGs was mainly due to the direct effect of the change in bacterial community and horizontal gene transfer (HGT) via the class 1 integron-integrase gene (intI1), but antibiotics indirectly influenced ARG profiles. The migration of ARGs in deep layer sediments was not related to the bacterial community and intI1, but may be explained by antibiotic selective effects and ARG transformation.

Impact of sediment characteristics on adsorption behavior of typical antibiotics in Lake Taihu, China

Sediment adsorption is one of the main fates of antibiotics in aquatic environments. However, few studies have compared the physicochemical properties of sediments from the same aquatic ecosystem but at different locations and correlated them with antibiotic adsorption efficiency. To predict the adsorption of antibiotics in water–sediment systems more accurately, this study conducted experiments with tetracycline (TC) and oxytetracycline (OTC) in tetracyclines, ciprofloxacin (CIP) in fluoroquinolones, and roxithromycin (ROX) in macrolides. Sediments from different locations in Lake Taihu, China, were collected to determine the adsorption properties of CIP, TC, OTC, and ROX. Moreover, the physicochemical properties of the sediments were measured and the correlation between these properties and antibiotic adsorption were discussed to establish a model for predicting adsorption parameter Kd. The antibiotic adsorption performance of sediments was high in heavily polluted and grassy areas but poor in estuarine areas of the lake, suggesting that adsorption effectiveness was affected by the physicochemical properties of sediments. Based on the established model, the specific surface area, organic carbon, and cation exchange capacity played the most significant roles. The study further determined that the predicted and actual values showed a good linear fitting relationship. Therefore, the model effectively predicted the antibiotic adsorption performance of different sediments and provided recommendations for the environmental trend and risk assessment of antibiotics.

A Remediation Study of Contaminated Marine Sediment through Application of Naturally Developed Oxygen Releasing Compound

Blocking the influx of nutrients from contaminated sediment and reducing terrigenous loads are essential to control eutrophication in coastal water areas. In this study, the use of an oyster-shell-based ORC (oxygen-releasing compound) was investigated with respect to nutrients such as nitrogen, phosphorous, and sulfur compounds in the sediment environment. The ORC, which was produced by pyrolyzing oyster shell powder, was found to be overoxidized and consisted of calcium peroxide. A series of experiments simulating a typical overlying water-sediment system were carried out in open-lid cylindrical columns over the fifteen-day experimental period. The elution and distribution of crucial contaminating species within that system are discussed. T-N, NH4 +-N, T-P, and Pi propagated with time toward the overlying water from the sediment through diffusive migration, showing a constrained increase over distance at the sediment-water interface. The nitrate levels decreased with time, possibly due to local denitrification. Partial oxidation in a homogenized mixture of sediment and oxidized oyster shell powder resulted in an increased DO level within the experimental time frame, which in turn caused T-N, NH4 +-N, T-P, and Pi to propagate at a lower rate than sediment without any ORC. Analyses for sulfates and sulfides in the sediment mixed with ORC confirmed that the chemical environment changed into a more oxidized state in fifteen days. Diffusive migration, along with chemical reactions and/or adsorption, successfully explained the propagation and distribution of the concerned nutrient species resulting from the use of oyster shell powders.