Degradation of rizazole in water–sediment systems

This study investigated the degradation of rizazole in water-sediment systems (West Lake system, WL; Beijing–Hangzhou Grand Canal system, BG) with two different types of sediments under aerobic and anaerobic conditions. The half-lives of rizazole in the WL water phase (14.59–15.13 d) were similar to those in the BG water phase (15.90–16.46 d). Within 3–7 d, the rizazole concentration in the sediments reached the maximum values, i.e., equilibrium. Rizazole dissipation was faster in the WL sediment phase with higher organic matter content (T_1/2 = 18.99–19.09 d) compared with the BG sediment phase (T_1/2 = 31.08–33.32 d). Rizazole degradation was slightly faster in the West Lake water-sediment system (WL system) (T_1/2 = 17.11–18.05 d) than in the Beijing–Hangzhou Grand Canal water—sediment system (BG system) (T_1/2 = 20.51–25.02 d). The aerobic degradation of rizazole was similar to its anaerobic degradation in the water-sediment system. The findings are useful to understand the behavior of pesticide in environment.     

Interaction between nitrogen and phosphorus cycles in mining-affected aquatic systems—experiences from field and laboratory measurements

The main objectives of this study were to (a) study the interaction between N and P cycles in mining-affected aquatic systems and (b) to quantify release rates of sedimentary soluble reactive phosphorus (SRP) that may be related to this interaction. Sediment cores and water from Lake Bruträsket (Boliden, northern Sweden) were collected and a time series of water sampling and flow measurements was conducted in the Brubäcken stream connected to the lake. Factors affecting SRP release were studied in a sediment incubation experiment and water column experiments. Field and laboratory measurements indicated that pH and dissolved oxygen are two important factors for SRP release. At the end of the low-oxygen incubation, an SRP concentration of 56 μg?L^?1 resulted in a sedimentary flux of 1.1 mg SRP?m^?2?day^?1. This is ～10 times higher than the flux of 0.12 mg SRP?m^?2?day^?1 obtained from depth integration of vertical SRP profiles measured in the lake, and ～100 times higher than the external flux of 0.014 mg SRP?m^?2?d^?1 into the lake (based on catchment area). Field measurements indicated that oxidation of organic matter and mining-related chemicals (ammonium and thiosulphates) may result in increased internal SRP flux from the sediment. Increased P loading in the lake as a result of low-oxygen conditions could change water column total nitrogen/total phosphorus ratios from 27 to 17, consequently changing the lake from being P-limited to be co-limited by N and P. The obtained findings point to possible interaction between the cycles of nitrogen (oxygen consumption) and P (flux from sediment) that may be important for nutrient regulation in mine water recipients.     

An experimental ecotoxicological study and its application to the behavioural study of organic mercury (CH3HgCl) in the environment: influence of temperature and pH

Laboratory experiments were carried out to study the influence of temperature (24, 28 and 30 °C) and pH (1–10) on organic mercury (CH₃HgCl) transfer and accumulation in an experimental ecotoxicological model. We followed the evolution of CH₃HgCl in a basic model (water+air) by varying temperature and pH. In a second step, we completed the model by adding sediment and fish. We added CH₃HgCl to water at the beginning of each experiment which was repeated at least three times. Results demonstrated that mercury was released from methylmercury into the air regardless of water pH and its concentration in the air increased with increasing pH. By contrast, in presence of sediment, almost all the mercury was fixed onto the sediment and no mercury was traced in air or in water. Interestingly, in the presence of sediment, the life span of fish under methylmercury exposure lasted longer despite their higher mercury body level content at their death. These results indicate that water is a bad exposure indicator for aquatic pollution. In case of chronic pollution, sediments, fish and aquatic plants are more appropriate indicators.     

Sediment-water distribution of perfluorooctane sulfonate (PFOS) in Yangtze River Estuary

Analysis of Perfluorooctane sulfonate (PFOS) distribution in water and sediment in Yangtze River Estuary showed that the estuary was a sink for PFOS. Salinity was an important parameter in controlling the sediment-water interactions and the fate or transport of PFOS in the aquatic environment. As the salinity (S‰) increased from 0.18 to 3.31, the distribution coefficient (K_d) between sediment and water linearly increased from 0.76 to 4.70 L g⁻¹. The study suggests that PFOS may be carried with the river water and transported for long distances before it reaches to the sea and largely scavenged to the sediment in the estuaries due to the dramatic change in salinity.     

Comparative distribution, sourcing, and chemical behavior of PCDD/Fs and PCBs in an estuary environment

PCDD/F and PCB field data (1041 samples) in five media (dissolved, suspended sediment, bed sediment, catfish, and blue crab) were studied to explore dual contaminant patterns in the Houston Ship Channel, Texas, USA. PCDD/Fs showed greater concentration than PCBs in suspended sediments while PCBs were higher in apparent dissolved (truly dissolved + DOC-associated), fish, and crab. PCDD/Fs at nearly all locations contributed more strongly to dioxin-like toxicity. The fraction of PCB TEQ was, however, enriched in biotic over abiotic media due in large part to the presence of PCB 126, which was mostly undetected in water and sediment and yet exhibited a BAF three times greater than 2,3,7,8-TCDD. Dissolved-suspended sediment and suspended-bed sediment relationships showed that (1) observed apparent dissolved concentration differences (as fraction of total water were mean 10% PCDD/Fs and 63% PCBs) can reasonably be explained by a four-phase partition model (truly dissolved, DOC-associated, suspended OC, and suspended BC) for PCBs but not for PCDD/Fs and (2) the contaminants behaved similarly in bed to suspended sediment concentration ratios (C_bed/C_susp) upstream of a major confluence but not downstream. PCA-cluster analysis pointed to the possibility that suspended sediment PCB contamination originates from resuspended bed sediment while PCDD/Fs in suspended sediment originates more probably from other sediment sources such as upstream wash load or air deposition. Finally, examinations of a congener marker ratio (PCB 209/206) seemed to indicate that a source of pure PCB 209 may exist in bed sediment near Patrick Bayou though the source was not completely localized.     

Influence of algal bloom degradation on nutrient release at the sediment–water interface in Lake Taihu, China

Algal bloom could drastically influence the nutrient cycling in lakes. To understand how the internal nutrient release responds to algal bloom decay, water and sediment columns were sampled at 22 sites from four distinct regions of China’s eutrophic Lake Taihu and incubated in the laboratory to examine the influence of massive algal bloom decay on nutrient release from sediment. The column experiment involved three treatments: (1) water and sediment (WS); (2) water and algal bloom (WA); and (3) water, sediment, and algal bloom (WSA). Concentrations of dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), ammonium (NH ₄ ⁺ -N), and orthophosphate (PO ₄ ^3? -P) were recorded during incubation. The decay of algal material caused a more rapid decrease in DO than in the algae-free controls and led to significant increases in NH ₄ ⁺ -N and PO ₄ ^3? -P in the water. The presence of algae during the incubation had a regionally variable effect on sediment nutrient profiles. In the absence of decaying algae (treatment WS), sediment nutrient concentrations decreased during the incubation. In the presence of blooms (WSA), sediments from the river mouth released P to the overlying water, while sediments from other regions absorbed surplus P from the water. This experiment showed that large-scale algal decay will dramatically affect nutrient cycling at the sediment–water interface and would potentially transfer the function of sediment as “container” or “supplier” in Taihu, although oxygen exchange with atmosphere in lake water was stronger than in columns. The magnitude of the effect depends on the physical–chemical character of the sediments.     

Effects of sediment burial disturbance on macro and microelement dynamics in decomposing litter of <Emphasis Type="Italic">Phragmites australis</Emphasis> in the coastal marsh of the Yellow River estuary,China

From April 2008 to November 2009, a field decomposition experiment was conducted to investigate the effects of sediment burial on macro (C, N) and microelement (Pb, Cr, Cu, Zn, Ni, and Mn) variations in decomposing litter of Phragmites australis in the coastal marsh of the Yellow River estuary. Three one-off sediment burial treatments [no sediment burial (0 mm year^?1, S₀), current sediment burial (100 mm year^?1, S₁₀), and strong sediment burial (200 mm year^?1, S₂₀)] were laid in different decomposition sites. Results showed that sediment burials showed significant influence on the decomposition rate of P. australis, in the order of S₁₀ (0.001990 day^?1)?≈?S₂₀ (0.001710 day^?1)?>?S₀ (0.000768 day^?1) (p?<?0.05). The macro and microelement in decomposing litters of the three burial depths exhibited different temporal variations except for Cu, Zn, and Ni. No significant differences in C, N, Pb, Cr, Zn, and Mn concentrations were observed among the three burial treatments except for Cu and Ni (p?>?0.05). With increasing burial depth, N, Cr, Cu, Ni, and Mn concentrations generally increased, while C, Pb, and Zn concentrations varied insignificantly. Sediment burial was favorable for C and N release from P. australis, and, with increasing burial depth, the C release from litter significantly increased, and the N in litter shifted from accumulation to release. With a few exceptions, Pb, Cr, Zn, and Mn stocks in P. australis in the three treatments evidenced the export of metals from litter to environment, and, with increasing burial depth, the export amounts increased greatly. Stocks of Cu and Ni in P. australis in the S₁₀ and S₂₀ treatments were generally positive, evidencing incorporation of the two metals in most sampling times. Except for Ni, the variations of C, N, Pb, Cr, Cu, Zn, and Mn stocks in P. australis in the S₁₀ and S₂₀ treatments were approximated, indicating that the strong burial episodes (S₂₀) occurred in P. australis marsh in the future would have little influence on the stocks of these elements. With increasing burial depths, the P. australis was particularly efficient in binding Cu and Ni and releasing C, N, Pb, Cr, Zn, and Mn, implying that the potential eco-toxic risk of Pb, Cr, Zn, and Mn exposure might be very serious. This study emphasized the effects of different burials on nutrient and metal cycling and mass balance in the P. australis marsh of the Yellow River estuary.     

Leaching of zinc from tire wear particles under simulated estuarine conditions

Tire wear particles (TWP) abraded from end-of-life passenger car tires have been added at a concentration of 1 g L⁻¹ to river water, sea water and mixtures thereof in order to examine the chemical controls on the leaching of Zn from the rubber matrix. Results of time-dependent experiments conducted over a period of 5 days were consistent with a diffusion controlled leaching mechanism with rate constants of about 0.04 mg L⁻¹ h^−1/2 in river water and between about 0.02 and 0.03 mg L⁻¹ h^−1/2 in sea water. Additional experiments revealed a reduction in Zn dissolution with both increasing salinity and pH and enhancement of leaching in the presence of fluorescent light compared with dark conditions. In corresponding experiments conducted in the presence of a fixed quantity (0.8 g L⁻¹) of clean, fractionated estuarine sediment, aqueous Zn concentrations were reduced by at least an order of magnitude. Increasing the quantity of sediment resulted in a progressive reduction in Zn concentration until an apparent equilibrium was achieved, with partition coefficients defining the sediment-water distribution of Zn of about 550 mL g⁻¹ and 270 mL g⁻¹ in river water and sea water, respectively. Results are interpreted in terms of the dissolution of ZnO and other residual complexes from the matrix and the subsequent, rapid adsorption of Zn²⁺ ions to coexistent estuarine sediment. The findings of the study are discussed in terms of their implications for the transport, fate and effects of TWP Zn in aquatic environments that are likely to receive urban runoff.     

Oxidation rates of SO2 in sea-water and sea-salt aerosols

The oxidation rates of sodium sulphite in bulk sea water solutions have been measured and found to be second order in [S(IV) ]. The reaction is much faster than in pure water due to chloride ion catalysis. The rate of absorption of SO₂ into sea-salt aerosols at various relative humidities has also been studied using a radioactive tracing technique. The reaction was found to be zero order in gas phase SO₂ concentration over the range 0.1–2 ppm. The reaction rate in the aerosols is several orders of magnitude faster than in sea water presumably due to the higher concentrations of Cl⁻ and other ions. The reaction rates both in the bulk solutions and in the aerosols were found to be faster for artificially prepared ‘sea water’ than for natural sea water, probably due to the absence of organic inhibitors.The conversion rates of SO₂ in marine or coastal atmospheres due to this reaction are estimated for various salt concentrations and relative humidities. In favourable circumstances it could be competitive with other mechanisms. A possible effect of this reaction on the deposition rate of SO₂ to the sea is noted.     

Degradation kinetics of tebufenozide in model aquatic systems under controlled laboratory conditions

Abstract

The hydrolysis of the insecticide tebufenozide was studied in the dark at 20 to 40°C in buffered (pH 4 to 10) distilled water, and at 20°C in unbuffered, sterilized and unsterilized stream water. Tebufenozide was very stable in acidic and neutral buffers at 20°C and the corresponding pseudo‐first‐order rate constants (k_obsd) and half‐lives (T_1/2) were 5.946 × 10^‐4 and 13.10 × 10^‐4 d^‐1, and 1166 and 529 d, respectively. The hydrolytic degradation was dependent on pH and temperature. At pH 10 and at 20,30 and 40°C, the k_obsd (10^‐4 d^‐1) and T_1/2 (d) values were 34.22, 66.72 and 130.0; and 203, 104 and 53.3, respectively. The energy of activation (E_a) values for the hydrolysis of tebufenozide at pH 4, 7 and 10, calculated from the Arrhenius plots, were 83.50, 66.71 and 50.87 kJ/mol, respectively. Tebufenozide was stable in sterilized stream water in the dark (T_1/2 = 734 d) but it degraded fairly rapidly in unsterilized stream water (T_1/2 = 181 d). Sunlight photodegradation of the chemical was slower (T_1/2 = 83.0 h) than the photolysis by ultraviolet radiations (T_1/2 values at 254 and 365 nm were 9.92 and 27.6 h, respectively); nevertheless, it was still appreciable during the summer months at 46°31’ N latitude. The differences in degradation rates between the unsterilized and sterilized stream water and the degradation of the chemical in the sterile, distilled water in sunlight, suggests that microbial processes and photolysis are the two main degradative routes for tebufenozide in natural aquatic systems.     

Sorption of Isoxaflutole Diketonitrile Degradate (DKN) and Dicamba in Unsaturated Soil

When analyzing the sorption characteristics of weakly sorbing or labile pesticides, batch methods tend to yield a high margin of error attributable to errors in concentration measurement and to degradation, respectively. This study employs a recently developed unsaturated transient flow method to determine the sorption of isoxaflutole's herbicidally active diketonitrile degradate (DKN) and dicamba. A 20-cm acrylic column was packed with soils with varied texture that had been uniformly treated with ¹⁴C-labeled chemical.

The antecedent solution herbicide in equilibrium with sorbed phase herbicide was displaced by herbicide-free water, which was infiltrated into the column. Sorption coefficients, K_d, were obtained from a plot of total herbicide concentration in the soil versus water content in the region where the antecedent solution accumulated. DKN K_d values were ～2–3 times (average K_d = 0.71 L kg^?1) greater using the unsaturated transient flow method as compared to the batch equilibration method in clay loam (K_d = 0.33 L kg^?1), but similar for the two methods in sand (0.12 vs 0.09 L kg^?1) soils. Dicamba K_d values were 3 times greater using the unsaturated transient flow method as compared to the batch equilibration method in the clay loam soil (0.38 vs 0.13 L kg^?1), however, the K_d values were the same for the two methods in the sand (～0.06 L kg^?1). This demonstrates that to determine sorption coefficients for labile hydrophilic pesticides, an unsaturated transient flow method may be a suitable alternative to the batch method. In fact, it may be better in cases where transport models have overpredicted herbicide leaching when batch sorption coefficients have been used.     

Analysis of a Summertime PM2.5 and Haze Episode in the Mid-Atlantic Region

Abstract

Observations of the mass and chemical composition of particles less than 2.5 μm in aerodynamic diameter (PM_2.5), light extinction, and meteorology in the urban Baltimore-Washington corridor during July 1999 and July 2000 are presented and analyzed to study summertime haze formation in the mid-Atlantic region. The mass fraction of ammoniated sulfate (SO₄ ^2-) and carbonaceous material in PM_2.5 were each ～50% for cleaner air (PM_2.5 < 10 μg/m³) but changed to ～60% and ～20%, respectively, for more polluted air (PM_2.5 > 30 μg/m³). This signifies the role of SO₄ ^2- in haze formation. Comparisons of data from this study with the Interagency Monitoring of Protected Visual Environments network suggest that SO₄ ^2? is more regional than carbonaceous material and originates in part from upwind source regions. The light extinction coefficient is well correlated to PM_2.5 mass plus water associated with inorganic salt, leading to a mass extinction efficiency of 7.6 ± 1.7 m²/g for hydrated aerosol. The most serious haze episode occurring between July 15 and 19, 1999, was characterized by westerly transport and recirculation slowing removal of pollutants. At the peak of this episode, 1-hr PM_2.5 concentration reached ～45 μg/m³, visual range dropped to ～5 km, and aerosol water likely contributed to ～40% of the light extinction coefficient.     

Mass balance modeling to elucidate historical and continuing sources of dioxin into an urban estuary

Polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins) are typically found in sediment, water and tissue as in the case of the Houston Ship Channel and Upper Galveston Bay (HSC–UGB) in Texas studied in this research. While hydrodynamic and fate and transport models are important to understand dioxin distribution in the various media, it is difficult to assimilate modeling results into a decision framework without appropriate tools that can aid in the interpretation of the simulated data. This paper presents the development of a mass-balance modeling tool linked to RMA2 and WASP models of the HSC–UGB system for 2002–2005. The mass-balance tool was used to aggregate modeling results spatially and temporally and estimate the relative contribution of sediments to dioxin loading into the Channel in comparison to runoff, deposition, and permitted effluent discharges. The total sediment associated-dioxin load into the system calculated using the mass balance model was 2.34 × 10⁷ ng d⁻¹ (almost 86% of the toxic equivalent load), and the re-deposited load to the sediment from the water column was 1.48 × 10⁷ ng-TEQ d⁻¹, such that 8.6 × 10⁶ ng-TEQ d⁻¹ or approximately 69% of the average daily dioxin flux is transported between model segments as sediment. The external loads to the system contribute approximately 3.83 × 10⁶ ng-TEQ d⁻¹, a value that is an order of magnitude smaller when compared to the contribution from sediment. These findings point to the need for sediment remediation strategies that take into account the spatial locations within the system that serve as sediment sources to dioxin in the water column.     

Non-linear regression model for spatial variation in precipitation chemistry for South India

Chemical composition of rainwater changes from sea to inland under the influence of several major factors – topographic location of area, its distance from sea, annual rainfall. A model is developed here to quantify the variation in precipitation chemistry under the influence of inland distance and rainfall amount. Various sites in India categorized as ‘urban’, ‘suburban’ and ‘rural’ have been considered for model development. pH, HCO₃, NO₃ and Mg do not change much from coast to inland while, SO₄ and Ca change is subjected to local emissions. Cl and Na originate solely from sea salinity and are the chemistry parameters in the model.Non-linear multiple regressions performed for the various categories revealed that both rainfall amount and precipitation chemistry obeyed a power law reduction with distance from sea. Cl and Na decrease rapidly for the first 100 km distance from sea, then decrease marginally for the next 100 km, and later stabilize. Regression parameters estimated for different cases were found to be consistent (R² ～ 0.8). Variation in one of the parameters accounted for urbanization. Model was validated using data points from the southern peninsular region of the country. Estimates are found to be within 99.9% confidence interval.Finally, this relationship between the three parameters – rainfall amount, coastline distance, and concentration (in terms of Cl and Na) was validated with experiments conducted in a small experimental watershed in the south-west India. Chemistry estimated using the model was in good correlation with observed values with a relative error of ～5%. Monthly variation in the chemistry is predicted from a downscaling model and then compared with the observed data. Hence, the model developed for rain chemistry is useful in estimating the concentrations at different spatio-temporal scales and is especially applicable for south-west region of India.     

Distribution,source, and environmental risk assessment of phthalate esters (PAEs) in water,suspended particulate matter,and sediment of a typical Yangtze River Delta City,China

Phthalates (PAEs) in drinking water sources such as the Yangtze River in developing countries had aroused widespread concern. Here, the water, suspended particulate matter (SPM), and sediment samples were collected from 15 sites in wet and dry seasons in Zhenjiang, for the determination of six PAEs (DMP, DEP, DIBP, DBP, DEHP, and DOP) using the solid-phase extraction (SPE) or ultrasonic extraction coupled with gas chromatography-mass spectrometry (GC-MS). The total concentrations of six PAEs (Σ₆PAEs) spanned a range of 2.65–39.31 μg L^?1 in water, 1.97–34.10 μg g^?1 in SPM, and 0.93–34.70 μg g^?1 in sediment. The partition coefficients (K_d1) of PAEs in water and SPM phase ranged from 0.004 to 3.36 L g^?1 in the wet season and from 0.12 to 2.84 L g^?1 in the dry season. K_d2 of PAEs in water and sediment phase was 0.001–9.75 L g^?1 in the wet season and 0.006–8.05 L g^?1 in the dry season. The dominant PAEs were DIBP, DBP, and DEHP in water and SPM, DIBP, DEHP, and DOP in sediment. The concentration of DBP in water exceeded the China Surface Water Standard. The discharge of domestic sewage and industrial wastewater might be the main potential sources of PAEs. The risk quotient (RQ) method used for the risk assessment revealed that DBP (0.01 < RQ < 1) posed a medium risk, while DIBP and DEHP (RQ > 1) posed a high environmental risk in water, DIBP (RQ > 1) also showed a high risk in sediment.

     

Sorption of atrazine and phenanthrene by organic matter fractions in soil and sediment

Atrazine and phenanthrene (Phen) sorption by nonhydrolyzable carbon (NHC), black carbon (BC), humic acid (HA) and whole sediment and soil samples was examined. Atrazine sorption isotherms were nearly linear. The single-point organic carbon (OC)-normalized distribution coefficients (K_OC) of atrazine for the isolated HA1, NHC1 and BC1 from sediment 1 (ST1) were 36, 550, and 1470 times greater than that of ST1, respectively, indicating the importance of sediment organic matter, particularly the condensed fractions (NHC and BC). Similar sorption capacity of atrazine and Phen by NHC but different isotherm nonlinearity indicated different sorption domains due to their different structure and hydrophobicity. The positive relationship between (O + N)/C ratios of NHC and atrazine log K_OC at low concentration suggests H-bonding interactions. This study shows that sediment is probably a less effective sorbent for atrazine than Phen, implying that atrazine applied in sediments or soils may be likely to leach into groundwater.     

Influence of competing inorganic cations on the ion exchange equilibrium of the monovalent organic cation metoprolol on natural sediment

The aim of this study was to systematically investigate the influence of the mono- and divalent inorganic ions Na⁺ and Ca²⁺ on the sorption behavior of the monovalent organic cation metoprolol on a natural sandy sediment at pH = 7. Isotherms for the beta-blocker metoprolol were obtained by sediment–water batch tests over a wide concentration range (1–100 000 μg L^?1). Concentrations of the competing inorganic ions were varied within freshwater relevant ranges. Data fitted well with the Freundlich sorption model and resulted in very similar Freundlich exponents (n = 0.9), indicating slightly non-linear behavior. Results show that the influence of Ca²⁺ compared to Na⁺ is more pronounced. A logarithmic correlation between the Freundlich coefficient K_Fr and the concentration or activity of the competing inorganic ions was found allowing the prediction of metoprolol sorption on the investigated sediment at different electrolyte concentrations. Additionally, the organic carbon of the sediment was completely removed for investigating the influence of organic matter on the sorption of metoprolol. The comparison between the experiments with and without organic carbon removal revealed no significant contribution of the organic carbon fraction (0.1%) to the sorption of metoprolol on the in this study investigated sediment. Results of this study will contribute to the development of predictive models for the transport of organic cations in the subsurface.     

Effect of salinity and sediment characteristics on the sorption and desorption of perfluorooctane sulfonate at sediment-water interface

This study investigated the influence of solution salinity, pH and the sediment characteristics on the sorption and desorption of perfluorooctane sulfonate (PFOS). The results showed that the sorption of PFOS onto sediment increased by a factor of 3 as the CaCl₂ concentration increased from 0.005 to 0.5 mol L⁻¹ at pH 7.0, and nearly 6 at pH 8.0. Desorption hysteresis occurred over all salinity. The thermodynamic index of irreversibility (TII) values increased with increasing concentration of CaCl₂. Maximum irreversibility was found in the sorption systems with CaCl₂ in the concentration of 0.5 mol L⁻¹. The results suggested that PFOS can be largely removed from the water with increasing salinity, and get trapped onto sediments irreversibly. These phenomena could be explained by salting-out effect and Ca-bridging effect. Studies also suggested that the content of total organic carbon is the dominant psychochemical properties of sediment controlling the sorption of PFOS.     

黄河兰州段悬移质泥沙对氨氮的吸附特性

实验研究了黄河兰州段不同粒径的悬浮泥沙对氨氮的吸附行为,拟阐释黄河兰州段水质自净的机制。通过分析探讨了含沙量、氨氮初始浓度、泥沙粒径和化学成分对氨氮吸附过程的影响。结果表明,准二级动力学方程和Langmuir模型能够较好地描述黄河兰州段不同粒径泥沙的吸附动力学和等温吸附过程(R20.9);含沙量对泥沙吸附氨氮作用具有显著影响,且氨氮吸附量和平衡时间与含沙量呈明显负相关性;氨氮初始浓度与氨氮吸附量及平衡时间呈正相关性;同时,泥沙颗粒越细,吸附氨氮的能力越强,吸附容量越大,反应的自发程度越高。此外,泥沙有机质、Fe2O3、Al2O3和MgO的含量随粒径减小而增大,它们对单位质量泥沙最大吸附量(Sm)具有正效应。泥沙的吸附在黄河兰州段水质自净过程中起着一定的促进作用。     

Phosphorus partitioning between sediment and water in the riparian wetland in response to the hydrological regimes

Water quality in watersheds is severely impacted by nutrient enrichment as a result of agricultural activities. Understanding hydrological effects on P dynamics can optimize the ecological function of riparian wetlands to reduce nonpoint source pollution. The XiaZhuHu wetlands were selected for field P investigation, and two typical hydrological batch studies of 35 d each (a static column observation simulating the dry season, and a steady-flow flume observation simulating the rainy season) were conducted to understand sediment P dynamics and evaluate capacity of P immobilization. The average equilibrium P concentration of 0.02 mg L^?1 among the 31 sampled sediments was generally lower than the average dissolved reactive P concentrations in the overlying water, indicating an ecological role as a P sink. In static simulation observation, there was a fast-pace sorption process during the first 3 d followed by a slower paced process, and the mass of P adsorbed per unit sediment surface (MPAS) reached 0.16 mg cm^?2. The temporal curves of P equilibrium between flowthrough water and top sediment (5 cm) were characterized as a quasi “V”-pattern, and the MPAS ranged from ?0.04 to 0.46 mg cm^?2 during the steady-flow observation. The newly-trapped P was mainly found in Al-bound P and subsequently as Fe-bound P, which would be helpful for sediment P immobilization. Based on our findings, the sediment of the tested wetlands could retain external P from agricultural land by as much as 10–30 times the area of itself, which accounts for approximately 3.3–10% of the watershed area.