[Denitrification Rates and nirS-type Denitrifying Bacteria Community Structure Characteristics of Bulk and Rhizosphere Soil in Spring and Summer in the Alpine Wetlands of the Qinghai-Tibet Plateau].

Denitrification is a key process in the nitrogen cycle of ecosystems. Most existing studies of nitrogen emissions and denitrifying bacterial communities are carried out in ecosystems with significant human interference, yet few focus in natural ecosystems with low human disturbance. Here, the denitrification rates and characteristics of nirS-type denitrifying bacterial communities in rhizosphere and bulk soils from alpine wetland plants at different altitudes(Tangke, Jiuzhi, Maduo, and Dari) and seasons(spring and summer) in the Yellow River source region of the Qinghai-Tibet Plateau were investigated. The 15N isotope tracer technique was used to estimate the denitrification rates, and high-throughput sequencing technology was used to determine the composition and relative abundance of nirS-type denitrifying bacterial communities. We also investigated the environmental factors(temperature and altitude) and soil physical and chemical properties(pH, soil organic carbon, ammonia, nitrate, and nitrite) controlling the denitrification and related microorganisms. The results show that the denitrification rates of alpine wetland soils ranged from 0.80 to 14.98 nmol·(g·h)-1, and the contribution to the total N2 production ranged from 11.23% to 71.16%. The soil samples from Tangke, Jiuzhi, and Dari showed higher denitrification rates in rhizosphere soils than the corresponding bulk soils(P<0.05). Proteobacteria was the most dominate denitrifying bacteria phylum. At the genus level, unclassified Proteobacteria(2.86%-29.41%) showed the highest relative abundance, indicating that unique unidentified bacteria may dominate denitrification in these wetland soils. The genera with the next highest relative abundances were Pseudomonas(2.45%-26.52%) and Cupriavidus(0%-34.14%). Distance-based redundancy analysis showed that the community structure of the nirS-type denitrifying bacteria was mainly affected by altitude, pH, and nitrite concentrations; Pearson correlation analysis showed that denitrification rates and the Shannon index are significantly negatively correlated with soil pH(P<0.05), and the relative abundance of the main denitrifying bacterial genera were influenced by temperature and soil pH(P<0.05). This study provides valuable insights for understanding the nitrogen cycle in the unique alpine wetlands of the Qinghai-Tibet Plateau.

[Irreversible sorption of phthalate acid esters to river sediments].

Irreversible sorption behavior of two phthalate acid esters (PAEs), Dimethyl phthalate (DMP) and Di-(2-ethyl-hexyl) phthalate (DEHP), on four natural sediment samples from the Yangtze River and the Yellow River has been studied by equilibrium sorption and multiple cycles of adsorption/desorption experiments. The equilibrium sorption experiment results showed that the organic carbon-normalized partition coefficients (lgKoc) of DMP and DEHP were higher than those reported in references. This means that the sorption of DMP and DEHP on natural sediments include other sorption mechanisms besides the linear partition on organic carbon. The multiple cycles of adsorption/desorption experiment results showed that the sorption of PAEs included linear reversible sorption and irreversible sorption. For the four sediment samples, the maximum of irreversible sorption capacities were 125.19-337.37 microg/g and 515.89-591.41 microg/g for DMP and DEHP, respectively, which were positive correlated to the surface areas, cation exchange capacity and black carbon content of the sediments. The OC-normalized partition constants for the reversible compartment (lgk(oc)(rev)) were 3.69-4.98 L/kg for DMP; they were higher than those (lgKoc) reported in references, suggesting other reversible sorption mechanisms exist besides the linear partition on organic carbon. The lgk(oc)(rev) were 4.12-5.31 L/kg for DEHP; they were close to those (lgKoc) reported in references, suggesting the linear partition on organic carbon is the main reversible sorption mechanism. Although the physiochemical properties of DMP and DEHP are different, the OC-normalized partition constant for the irreversible compartment on the four sediments is essentially constant with lgk(oc)(rev) = (6.46 +/- 0.38) L/kg. As irreversible sorption exists for PAEs, the maximum of irreversible sorption capacity should be considered when studying the sediment quality criteria.

[Distribution characteristics of phthalic acid esters in the Wuhan section of the Yangtze River].

Samples of water and sediment were collected at 30 sites in Wuhan section of the Yangtze River in high and low water period. Phthalic acid esters (PAEs) concentrations in each sample were determined by Gas Chromatography. The results were shown as follows: (1) PAEs concentrations in water phase of lakes and tributaries ranged from 0.114-1.259 microg/L in high water period and 0.25-132.12 microg/L in low water period, while slight increasing trends could be discovered in the main stream (0.034-0.456 microg/L and 35.73-91.22 microg/L in high and low water period, respectively). (2) PAEs concentrations in sediment phase of tributaries and lakes in low water period were from 6.3 to 478.9 microg/g. Di-n-butyl phthalate (DBP) and di-(2-ethylhexyl) phthalate (DEHP) both had strong trends from water to sediment phase, and the PAEs concentration ranges of the sediment phase in the main stream were 151.7-450.0 microg/g in high water period and 76.3-275.9 microg/g in low water period; DBP could transfer from sediment to water in high water period, while DEHP still had a potential for adsorption in low water period. (3) Among five studied PAEs compounds, DBP and DEHP were the main pollutants. According to the Surface Water Quality Criteria of China (GB 3838-2002), the limit values of DBP and DEHP for drinking water sources were 0.001 and 0.004 mg/L. All water samples in high water period were up to standard while the standard-exceeding sections accounted for 82.4% in low water period. (4) The PAEs pollution of the Wuhan section was similar to the Velino lake in Italy or the middle and lower stream of the Yellow River in China. However, PAEs concentrations in water phase of the Wuhan section in high water period were lower than most water bodies at home and abroad.

[Effect of suspended sediment on the transformation of organic nitrogen].

Microcosm experiments have been carried out to study the effects of suspended sediment on the transformation of organic nitrogen contaminants under different conditions, including with and without spiking bacteria to the water-sediment system. When with the natural water and sediment as cultivation media and without spiking bacteria to the water system, the presence of sediment could stimulate the transformation of organic nitrogen, and the transformation rates were correlated well with the sediment concentration. When the initial concentration of organic nitrogen in the water system was 5 mg/L, and the suspended sediment content were 0, 5 and 10 g/L, the first-order transformation rate constants of organic nitrogen were 0.286,0.333 and 0.538 d(-1), respectively; the nitrification rate constants (K4) were 0.001 8, 0.003 8 and 0.0050 L x (d x micromol)(-1), respectively, when fitting the nitrification process with the Logistic kinetics. When spiking the water systems with the same initial bacteria density, the first-order transformation rate constants of organic nitrogen and nitrification rate constants (K4) increased with the sediment content. With the natural water and sediment as cultivation media, the mechanism regarding the effects of suspended sediment on organic nitrogen transformation includes the following aspects: (1) The initial amount of bacteria increased with the sediment content in the water system. (2) The growth of bacteria was promoted by the sediments, and bacteria tended to attach to the sediment. In addition, most of organic nitrogen was attached to the sediment phase and the transformation of organic nitrogen in the water system mainly occurred at the sediment/water interface. (3) The presence of sediment increased the contact chances between bacteria and organic nitrogen, thus stimulated the transformation of organic nitrogen contaminants.

[Reasons of high concentration ammonium in Yellow River, China].

Ammonium nitrogen contamination is one of the major problems of the Yellow River in China. The speciation, concentration and sources of nitrogen compounds as well as the water environment conditions of the Yellow River had been analyzed to study the reasons for the fact that the ammonium nitrogen concentration was above the water quality standard. In addition, laboratory experiments had been carried out to investigate the effects of suspended sediment (SS) on nitrification rate. The results indicated that the presence of SS could accelerate the nitrification process, therefore, the effects of SS on nitrification rate was not the reason for the high level of ammonium nitrogen in the river. The excessive and continuous input of nitrogen contaminants to the river was the fundamental reason for the high concentration of ammonium nitrogen. Organic and ammonium nitrogen with high concentration inhibitted the nitrification processes. When the initial NH4+ -N concentrations were 10.1, 18.4 and 28.2 mg/L, nitrification efficiencies were 17.4%, 13.0% and 2.5%, respectively. When the initial organic nitrogen concentrations were 5.5 and 8.6 mg/L, the maximum concentrations of ammonium nitrogen produced by the oxidation of organic nitrogen would reach 0.47 and 1.69 mg/L and they would last for 2 days and 6 days, respectively. The oxygen-consuming organics and toxic substance existing in the river water could inhibit the activity of nitrifying bacteria, and thus lead to the accumulation of ammonium nitrogen. In addition, the high pH value of river water resulted in the high concentration of nonionic ammonium nitrogen which would reduce the activity of nitrifying bacteria and decrease the nitrification rates. Besides, low river runoff, low SS content and low activity of nitrifying bacteria resulted in the high level of ammonium nitrogen of the river in the low water season.

[Pollution of polycyclic aromatic hydrocarbons (PAHS) in middle and lower reaches of the Yellow River].

Samples of water, suspended particulate matter (SPM) and sediment in the Yellow River was analyzed. The total concentration of PAHs in the main river varies from 179 ng/L to 369 ng/L (sigma 15PAHs) in water, from 54 microg/kg to 155 microg/kg (sigma 13PAHs) in SPM dry weight, and from 31 microg/kg to 133 microg/kg (sigma 13PAHs) dry weight in sediment. The levels of PAHs in water of tributaries are higher than those in the corresponding sites in the main river, and concentrations of benzo(a)pyrene in most of the stations sampled are above drinking water standard. In SPM, PAHs of 3 to 6 benzene rings are mainly correlated to the content of total organic carbon (TOC) in different sites of the main river, while only 4 to 6 rings PAHs in sediment of main river are correlated to TOC for the influence of Mengzhou Canal, whose concentration of 3-ring PAHs are quite high. The distribution of PAHs in all media sampled in the main river indicates that PAHs are mainly transported from water into SPM between Mengzhou and Jiaogong Bridge, while in the reach between Jiaogong bridge and Huayuankou a great reduce of PAHs in SPM is mainly due to the diluting effect in the interchanging process between sediment and SPM. Source analysis also reveals that PAHs are mainly originating from coal burning, although in some tributaries PAH inputs could come from combustion of petroleum.

[Effect of particulate size and composition on the biodegradation of PAHS in nature waters].

Effect of particulate size and composition on the biodegradation of polycyclic aromatic hydrocarbons(PAHs) in nature waters was examined. Experimental study was carried out for the Yellow River. The results showed that the biodegradation of benzo[a] pyrene and chrysene in water system could be fitted with one-order kinetics and the existence of particulates promoted the biodegradation. When the particulate content was 4 g/L, the sequence of increasing trend in the PAH biodegradation rates was: water system with middle size particulates (7-25 microm) > water system with small size particulates (<7 microm) > water system with large size particulates (>25 microm). The biodegradation rate constants for benzo[a]pyrene in water systems with middle, small and large size particulates were 0.0248 d(-1), 0.0212 d(-1), 0.0192 d(-1), respectively, and that for chrysene were 0.0288 d(-1), 0.0261 d(-1), 0.0218 d(-1), respectively. The mechanisms regarding the effects of particulate size on the biodegradation of PAHs include several aspects. First, the particulate size and composition affected the PAHs degraders level in water system as well as the distribution of PAHs degraders in water and particulate phases. The population of PAHs-degraders in water systems with middle and small size particulates was higher than that with large size particulates. Second, PAHs tended to be sorbed on the particulate phase, and the desorption of PAHs from the particulate phase would lead to a higher concentration of PAHs in the interface between water and particulate phases. Since the PAHs-degraders also tended to grow in the interface between water and particulate phases, this would result in a higher contact chances for PAHs and PAHs-degraders. Therefore, the existence of particulates stimulated the biodegradation of PAHs in water system. Third, the sorption capacity of PAHs and PAHs-degraders on the middle and small size particulates was higher than that on the large size particulates. Consequently, the biodegradation rates of PAHs in water systems with middle and small size particulates were higher than that with large size particulates. However, the desorption capacity of PAHs from middle size particulates was higher than that from small size particulates, leading to that PAHs concentration in the water/particulate interface of the former system was higher than that of the latter system. Therefore, the biodegradation rates of PAHs in water system with middle size particulates were higher than that with small size particulates.

[Adsorption and partition of PAHS on particles of the Yellow River].

Experiments were carried out to study the sorption of PAHs Benzo(a)pyrene, chrysene and Benzo(g, h, i)perylene on particles of the Yellow River. The contributions of adsorption and partition to the sorption of PAHs were investigated. Several significant results were obtained from the study: (1) The total sorption capacity increases with the particle content while the sorption capacity of unit weight particle decreases; the isotherms of Benzo(a)pyrene depend on the particle content. (2) Isotherms of Benzo(a) pyrene can be fitted with the Dual Adsorption-Partition model under different particle content; the measured value of the adsorption and partition are in accord with the theoretical value of the Dual Adsorption-Partition model. (3) The adsorption is predominant in the sorption of Benzo(a)pyrene. When the particle contents are 3, 8 and 15 g/L and the liquid equilibrium concentrations are 2.84, 2.35 and 3.4 microg/L, respectively, the contributions of adsorption are 67.8%, 65.6% and 62.69%, respectively. In addition, the contributions of adsorption have a decreasing trend with the increase of the particle content. (4) The sorption capacity of Benzo (a) pyrene being alone are bigger than that with other PAHs chrysene and Benzo(g, h, i)perylene coexisting in the water system, this also proves that the adsorption is predominant in the sorption of PAHs.

[Effect of particles on the photodegradation of PAHs in natural waters of the Yellow River].

Photodegradation of chrysene, benzo(a)pyrene and benzo(ghi)perylene in natural water of the Yellow River was studied using simulation sunlight. The effects of particulates on the photodegradation were explored. Several results arose from this study: (1) The photodegradation of PAHs can be fitted with first-order kinetics when no particulates exist in water system, and the first-order constant increase with the decrease of initial concentration of PAHs. The photodegradation rates of the three PAHs are related to their molecule absorption spectrum. (2) The presence of loess exerts two kinds of effects on the photodegradation of PAHs, which include the inner filter effects and the photosensitizing effects of humic substance in Loess. These two opposite effects lead to the difference of net effects among different contents of loess. When the loess contents are 0.1 g/L and 5.0 g/L, the presence of loess stimulates the photodegradation of chrysene, benzo(a)pyrene. When the loess content is 5.0 g/L, the presence of loess stimulates the photodegradation of benzo(ghi)perylene. In addition, the photodegradation of PAHs can be fitted with the second-order kinetics when there is loess in the water system. (3) The dissolvable humic substances in loess can accelerate the photodegradation of PAHs while the indissoluble part cannot. (4) Since the dissolvable humic substances in the suspended solids of the river have been dissolved in water, the addition of suspended solids to the water system can only cause the decrease of photodegradation rate of PAHs due to its inner filter effects, and the photodegradation rate decreases with the suspended solid content as a power exponent function.

[Simulation of biodegradation of petroleum contaminants in natural waters of the Yellow River].

Petroleum contaminants is one of the major pollutants in the Yellow River. Laboratory simulation experiments were carried out to study the natural biodegradation of the petroleum contaminants. When adding 10 mg/L petroleum contaminants to the Yellow River water samples containing 0 or 0.5 g/L sediment, the petroleum contaminants-degrading bacteria increased gradually after about one week of acclimatization. With the sediment content of 0.5 g/L, about 85% petroleum contaminants with the initial concentration of 11.64 mg/L in river water could be degraded within 63 days at 20 degrees C. The biodegradation rate was greatly influenced by the sediment content and the initial concentration of petroleum contaminants, and such effect was different from one degradation stage to another. In addition, the existence of sediment affected the biodegradation kinetics of petroleum contaminants.

[Influence of humic substance in solids on CODMn of the Yellow River].

Experiments were carried out to study the influence of humic substance in solids (Loess soil) on CODMn in the Yellow River. Several significant results were abtained from the study: (1) The total CODMn of water sample including liquid and solid phases increased significantly with the increase of solid content; The CODMn of liquid phase of water sample under pre-treatment with acid (LPWSPC) also increased significantly with the increase of solid content while that without pre-treatment did not increased significantly. (2) With the increasing of solid content, the total BOD5 of water sample increased much slower than the total CODMn and the CODMn of LPWSPC. (3) The humic substances with the content of 0.76% in solids (Loess soil) contributed greatly to the total CODMn of water sample. When the solid contents were 7.5 g/L and 15.0 g/L, the humic substances in solids accounted for 15.9% and 21.7% of the total CODMn of water sample, respectively. (4) When solid contents were 7.5 g/L and 15.0 g/L, fulvic acid,one of the main compositions of humic substance contributed to 23.6% and 50.6% of the CODMn of LPWSPC, respectively. Since the fulvic acid can hardly be biologically oxidized under natural conditions, the CODMn of LPWSPC in water quality monitoring exaggerates the oxygen-consuming organic contamination of the Yellow River.

Effects of common inorganic anions on the rates of photocatalytic degradation of sodium dodecylbenzenesulfonate over illuminated titanium dioxide.

Experiments were carried out to study the effects of several anions on the photocatalytic degradation rates of sodium dodecylbenzene sulphonate (DBS) with TiO2 as catalyst. The anions were added as Na2SO4, NaNO3, NaCl, NaHCO3, NaH2PO4 and Na3PO4, and two levels of anion content, i.e. 12 mmol/L and 36 mmol/L in terms of Na+, were studied. The results revealed that: Cl-, SO4(2-), NO3- and HCO3- retarded the rates of DBS degradation to different degrees; PO4(3-) increased the DBS degradation rate at low concentration and decreased the rate at high concentration; H2PO4- accelerated the rate of DBS degradation. The mechanism of the effects of anions on DBS degradation was concluded as the following three aspects: anions compete for the radicals; anions are absorbed on the surface of catalyst and block the active site of catalyst; anions added to the solution change the pH value and influence the formation of .OH radicals and the adsorption of DBS on catalyst.