Controllable Regioselective [3+2] Cyclizations of N-CF3 Imidoyl Chlorides and Ph3PNNC: Divergent Synthesis of N-CF3 Triazoles.

Presented herein are two distinct regiodivergent [3+2] cyclization reactions between N-CF3 imidoyl chlorides and N-isocyaniminotriphenylphosphorane (NIITP) that include flexible modulation of the electronic properties of NIITP. The regioselectivity of reactions was different in the absence and presence of the Mo catalyst. The approach provides alternative efficient and scalable routes for N-CF3 triazole synthesis, demonstrating a broad substrate scope, excellent functional group tolerance, and practical advantages.

N-CF3 Imidoyl Chlorides: Scalable N-CF3 Nitrilium Precursors for the Construction of N-CF3 Compounds.

A wide range of N-CF3 imidoyl chlorides were synthesized for the first time via the N-trifluoromethylation of nitriles in DCM by using AlCl3-activated PhICF3Cl as the CF3 source. The reactions of them with N-/O-/S-nucleophiles, as well as with 1,3-dipoles, were carried out to efficiently deliver N-CF3 amidines/imidates/thioimidates and N-CF3 azoles, demonstrating that they are a class of scalable NCF3-containing synthons in the synthesis of N-CF3 compounds.

[Contamination Characteristics and Source Apportionment of Soil Heavy Metals in an Abandoned Pyrite Mining Area of Tongling City, China].

To investigate the impact of pyrite mining on the heavy metal pollution in the surrounding soil in Tongling City, 50 surface soil and sediment samples were collected from mining fields, farmland, forests, villages, and the river. The contents of Zn, Cr, Cu, Pb, Ni, Cd, and As in soils and sediments were analyzed. Then, the spatial distribution characteristics of heavy metals in soil were analyzed, and the degree of heavy metal pollution and potential ecological risk level were assessed. Finally, the sources of soil heavy metal pollution were identified. In general, the soil in the study area was weakly acidic (average pH=6.32), and the contents of other heavy metals except Ni exceeded the background values of the soil in Tongling City. Moreover, Ni and Cd were enriched in the river sediments. According to the Nemerow pollution index, Pb and As reached heavy pollution levels, Cu and Cd reached moderate pollution levels, and other elements belonged to light or non-pollution levels. The comprehensive pollution index of different land types was ranked in the order of mining field > river > forest > farmland > village. Mining fields and the river were heavily polluted, forest land was moderately polluted, and farmland and villages were mainly mildly polluted. Pb, As, and Cd belonged to the medium ecological risk category. The contribution rates of the potential ecological risk index were 33.27%, 27.39%, and 20.22%, which were much higher than the other four elements. The ranking results of the potential ecological risk index of different land types was the same as that of the comprehensive pollution index. Mining fields and the river were at a high-risk level, forest land reached moderate risk, and the rest were at a slight risk level. The consistent results of correlation analysis, principal component analysis (PCA), and positive definite matrix factor analysis (PMF) indicated that Zn, Cu, Pb, Cd, and As were mainly derived from pyrite mining activities, Cr mainly came from the parent material and agricultural production, and Ni was mainly affected by soil-forming parent material and pyrite mining activities.

[Contamination Assessment and Source Apportionment of Soil Heavy Metals in Typical Villages and Towns in a Nonferrous Metal Mining City].

To investigate the soil contamination degree and potential ecological risk level of heavy metals in villages and towns in Tongling City, we collected 67 surface soil samples (including surface dusts and river sediments) from the typical districts, namely Shun'an Town, Zhongming Town, and Yi'an Economic Development Zone, and measured the contents of heavy metals including Cu, Zn, Pb, Cr, Cd, As, and Ni. Then, spatial distribution characteristics of heavy metals were analyzed, and their contamination degree and potential ecological risk were assessed. Finally, source apportionment of soil heavy metals was conducted using factor analysis. The results showed that the soil pH was weakly acidic in the study area, and the average contents of Cu, Zn, Cr, Cd, As, and Ni were 4.94, 2.89, 2.07, 0.94, 7.97, 4.03, and 2.02 times their soil background values in Tongling City, respectively. In general, the contents of soil heavy metals in the western part were higher than those in the eastern part across the studied area. According to the Nemerow pollution index, Cu, Cd, As, and Pb reached pollution levels; Zn, and Ni approached moderate pollution levels; and Cr belonged to the no pollution degree category. The Nemerow comprehensive pollution index of different land types was arranged in the order of river bed>town district>industrial land>vegetable land>agricultural land>mountain forest>village. On the whole, the contamination degree of soil heavy metals in the study area reached severe pollution levels. The order of potential ecological risk coefficients of soil heavy metals was Cd>As>Cu>Pb>Ni>Zn>Cr, in which Cd belonged to the extremely high risk level, Cu and As belonged to the medium risk level, and the others were all low risk levels. The potential ecological risk levels corresponding to different land types were as follows:river bed>town distribution>industrial land>vegetable land>agricultural land>village>mountain forest. The industrial land, vegetable land, and town district generally reached a very high risk level, and the agricultural land reached a high risk, whereas both village and mountain forest land showed a medium risk. Principal component analysis showed that Cu, Zn, Pb, Cd, and As in the study area were derived from local metal mining pollution; Cr was from both the geological background and metal mining pollution; and Ni mainly came from fossil fuel combustion.

Synthesis of N-CF3 Amidines/Imidates/Thioimidates via N-CF3 Nitrilium Ions.

An efficient methodology for the synthesis of a wide range of N-CF3 imidic acid derivatives is presented. In this reaction, N-CF3 nitrilium ions were generated via N-trifluoromethylation of nitriles using PhICF3Cl under catalysis with DMAP, followed by the capture of N-, O-, or S-centered nucleophiles to give diverse N-CF3 amidines, imidates, and thioimidates. The method provides a platform for preparing N-CF3 compounds with potential applications.

An N-Trifluoromethylation/Cyclization Strategy for Accessing Diverse N-Trifluoromethyl Azoles from Nitriles and 1,3-Dipoles.

N-Trifluoromethyl azoles are valuable targets in medicinal chemistry, but their synthesis is challenging. Classical preparation of N-CF3 azoles relies on the functional group interconversions but suffers from tedious N-pre-functionalization and unfriendly agents. Introduction of the CF3 onto the nitrogen of heterocycles provides a direct route to such motifs, but the N-trifluoromethylation remains underdeveloped. Reported here is an alternative and scalable cyclization strategy based on NCF3 -containing synthons for constructing N-CF3 azoles. The approach involves the N-trifluoromethylation of nitriles followed by a [3+2] cyclization between resulting N-CF3 nitrilium derivatives and 1,3-dipoles. PhICF3 Cl was an effective CF3 source for the transformation. As a result, a generic platform is established to divergently synthesize N-trifluoromethylated tetrazoles, imidazoles, and 1,2,3-triazoles by using sodium azide, activated methylene isocyanides, and diazo compounds as dipoles.

[Release Risk of Phosphorus by Sediments and Its Influencing Factors in Ponds and Ditches of a New Urban District Park].

This study examined five ponds and three ditches in the Shufengwan Sports Park in a new urban district of Hefei City, from which surface-layer sediments and overlying water samples were collected during autumn, winter, and summer. The equilibrium phosphate concentrations (EPC0) of the sediments and its response to exogenous carbon or nitrogen were then measured. The resulting EPC0values were used to assess the risk of phosphorus release by the sediments. Finally, major factors influencing phosphorous release were identified using the Partial Least Squares Regression (PLSR) method. The sediments in the urban park exhibited a light-to-moderate level of phosphorous pollution, with the total phosphorus content (TP) ranging from 209.28 to 713.51 mg·kg-1 and biologically available phosphorus accounting for 18.51%-36.21% of the total phosphorus content. Under ambient background, the EPC0 values in pond sediments were 0.012-0.142 mg·L-1, with a mean value of 0.057 mg·L-1, while in ditches the values ranged from 0.036 to 0.156 mg·L-1 with an average value of 0.078 mg·L-1. The addition of exogenous carbon increased the EPC0 values (by approximately 47.5% in pond 3), and thus increased the risk of phosphorus release from sediments, in pond 1, 3, and ditch 1. However, EPC0 values of the other ponds and ditches decreased (in particular, by approximately 58.6% in pond 5), indicating that the risk of phosphorus release decreased. After the addition of exogenous nitrogen, the EPC0 values of almost all ponds and ditches declined to varying degrees (except in ditches 1 and 2 during the summer). In particular, in the EPC0 value of pond 2 declined by approximately 51.6%. The declining values imply that nitrogen was a limiting factor in phosphorus uptake by sediments in ponds and ditches. According to the results of PLSR, nitrogen and phosphorus had different effects on the EPC0 values of sediments in ponds and ditches.

[Sediment Denitrification Rate and Its Response to Exogenous Carbon and Nitrogen in the Ponds and Bottomland of the Chaohu Lakeshore Zone].

From October 2018 to August 2019, three typical ponds and bottomland were selected in the Chaohu lakeshore zone, where surface sediments and overlying water samples were collected simultaneously. A set of incubation experiments, along with exogenous carbon and nitrogen concentration gradients, were conducted to analyze sediment denitrification rates and its response to carbon and nitrogen limitation. Moreover, the main influencing factors for the sediment denitrification process were identified using correlation analysis method. The results showed that ① the denitrification rates of three plant plexus sediments were 2.15-10.87, 2.08-10.65, and 2.06-10.88 mg·(kg·h)-1, with averages of 6.47, 6.97, and 6.76 mg·(kg·h)-1, respectively. Overall, there was no significant difference between them. ② In general, exogenous nitrogen addition could significantly increase denitrification rates of the three plant sediments, indicating that nitrate was the limiting factor for the sediment denitrification process. ③ Exogenous carbon addition resulted in a significant decrease in the denitrification rates of three plant plexus sediments, indicating that organic carbon inhibited the denitrification process. ④ Exogenous carbon and nitrogen added simultaneously displayed a dramatic effect on the increase of sediment denitrification rates. Except for the bottomland Pucao in October and pond Pucao in June, all other cases showed higher denitrification rates for high carbon and nitrogen concentration.

[Phosphorus Forms and Release Risk of Sediments in Urban Sewage Treatment Plant Effluent and Receiving Stream Reach].

From October 2018 to April 2019, the surface sediment and overlying water samples were collected every two months from the upstream and downstream of the effluent outlet of the Caitianpu sewage treatment plant in the Banqiao River, Hefei City. The effects of the sewage treatment plant effluent on both phosphorus forms and the equilibrium phosphate concentration (EPC0) in sediments were analyzed. The response of equilibrium phosphate concentration to external carbon (sodium acetate) and the release risk of phosphorus in sediments were investigated. Result show that the phosphorus pollution in Banqiao River was more severe. The average values of total phosphorus in the sediments at the upper and lower effluent outlet were 789.39 mg·kg-1 and 854.41 mg·kg-1, respectively, and the average bio-available phosphorus amounts were 157.19 mg·kg-1 and 173.37 mg·kg-1, respectively. The EPC0 values of the four sampling points decreased in the order SP1 > SP2 > SP3 > CP, indicating that the sewage treatment plant effluent increased the EPC0 level and phosphorus release risk of the stream sediments. Moreover, the addition of exogenous carbon significantly decreased the EPC0 value of the sediment, especially in SP1, suggesting that the addition of exogenous carbon decreased the risk of phosphorus release from sediments.

Epidemiology of myopia and unaided visual impairment of primary and secondary school students of Han and minorities in Mangshi City in Yunnan / 中国学校卫生

Objective@#To investigate the prevalence and associated factors of unaided visual impairment and myopia among primary and secondary school students in Yunnan Province, and to provide scientific basis for myopia prevention.@*Methods@#The study was conducted among primary and secondary school students in Mangshi, Yunnan Province from March to August, 2014. All the 7 681 subjects underwent detailed eye examinations and a questionnaire survey. Myopia was defined as spherical equivalent value of less than -0.5 diopters. Unaided visual impairment was analyzed on the basis of the better and the worse-seeing eye, respectively.@*Results@#The prevalence of myopia and high myopia were 39.1% and 0.6%. The prevalence of unaided visual impairment was 11.4% based on the worse-seeing eye. Refractive errors accounted for 87.3% of the participants with unaided visual impairment. Prevalence of myopia was higher in girls than in boys (χ2=29.74, P<0.01), but there was no gender difference in high myopia (P=0.19). The prevalence of myopia and high myopia increased significantly with increasing age (χ2=351.23, 22.56, P<0.01). Besides, prevalence of myopia was 63.7% in Dai nationality students and 36.6% in Yi nationality students (χ2=78.14, P<0.01), which was higher than other ethnic minorities. After adjusting for the effects of sex, age and ethnicity, the presence of myopia was associated with increasing height (OR=1.02, 95%CI=1.01-1.03), computer use (OR=1.17, 95%CI=1.03-1.32), having a myopic father (OR=1.56, 95%CI=1.24-1.94), having a myopic mother (OR=1.33, 95%CI=1.08-1.63) and more time reading(OR=1.18, 95%CI=1.09-1.28). High myopia was found to be more prevalent in children who had a myopic father (OR=3.98, 95%CI=1.72-9.22) and using computers (OR=2.31, 95%CI=1.17-4.57).@*Conclusion@#Myopia and unaided visual impairment is prevalent in school students in rural China (Yunnan), though the prevalence is relatively lower compared with other areas in China. Attention should be paid to the formulation and input of primary eye care policies.

[Potential for Phosphorus Uptake by Bed Sediments and Its Response to Carbon Additions in the Shiwuli River, Chaohu Lake Basin].

Surficial sediments were collected from five sampling sites in the mainstream of the Shiwuli River along an urban-rural gradient in the Chaohu Lake basin during July 2017 (summer) and January 2018 (winter). The total uptake (SPUlive), abiotic uptake (SPUkill), and biotic uptake (SPUbiotic) of phosphorus by sediments were measured, and uptake responses to different carbon sources (i. e., sodium acetate, glucose, and a mixture of both) were explored quantitatively through incubation experiments. The results showed that SPUlive had obviously spatiotemporal variations across the five sites, and SPUkill was higher than that of SPUbiotic. Under no carbon added, the mean values of SPUkill were 3.016 µg·(g·h)-1 and 3.368 µg·(g·h)-1, and the average values of SPUbiotic were 0.784 µg·(g·h)-1 and 0.323 µg·(g·h)-1 in summer and winter, respectively. Moreover, significant differences were found in abiotic phosphorus uptake between the two months. In the presence of carbon addition, both the value of SPUbiotic and the contribution rate of biotic phosphorus uptake showed a distinct increase. In general, the magnitude and rate of biotic uptake of phosphorus by sediments was highest when sodium acetate was added, followed by glucose, while the effect of mixed carbon was the worst. The responses of biotic phosphorus uptake to carbon addition suggested that the uptake potential of phosphorus by sediments in Shiwuli River was restricted by the carbon availability to some degree.

[Effects of Exogenous Carbon Addition on Equilibrium Phosphate Concentration and Risk of Phosphorus Release from Sediments in the Shiwuli River, Chaohu Lake Basin].

Five surface sediment samples were collected every two months from the Shiwuli River along an urban-rural gradient, Chaohu Lake Basin, from July 2017 to May 2018. Sediment phosphorus fractions were investigated, and equilibrium phosphate concentration (EPC0) and its response to exogenous carbon (sodium acetate) addition were explored. Moreover, the risk of phosphorus release from sediment into water column was also evaluated. Results show that the Shiwuli River was seriously polluted by phosphorus. The average values of total phosphorus content in sediments ranged from 915.04 to 1205.31 mg·kg-1, and it decreased slowly along the urban-rural gradient, while the bio-available phosphorus content remained stable. Exogenous carbon addition not only reduced the EPC0 values of sediments (about 29%), but changed the order of EPC0 values among the five sampling sites as well. In general, the ratio of overlying water SRP (soluble reactive phosphorus) concentration to EPC0 value was 66.7%, and phosphorus adsorption-desorption equilibrium saturation EPCsat<-20% accounted for about 60.0%, indicating that the surface sediments in the Shiwuli River were dominated by phosphorus adsorption, namely, keeping the phosphorus "sink" state. The inputs of exogenous carbon addition increased the proportion of EPCsat<-20% from 60.0% to 73.3%, which lowered the risk of phosphorus release from sediments.

[Nitrification Rates and Pollution Characteristics of Sediments with Different Geomorphic Features in the Shiwuli Stream, Chaohu Lake Basin].

Sediment and overlying water samples were collected seasonally from five different geomorphic structures (i.e., pools, riffles, gravel bars, point bars, and runs) from two urban reaches of the Shiwulihe River in the Chaohu Lake Basin dominated by high ammonia concentration between July 2017 and March 2018. Both the sediment potential and areal nitrification rates were measured and their seasonal and geomorphological variability were evaluated. The specific differences between every two geomorphic structures were determined using the Mann-Whitney U test and the relationship between the overlying water environment or benthic sediments and sediment nitrification was explored based on regression analysis. The results show that:① The studied reaches are seriously polluted by nitrogen and phosphorus and most of the oxidation-reduction potential (ORP) values in the overlying water were are below 0 mV, suggesting strong reducing conditions of the water column. ② The potential nitrification rates (PNRs) across the five geomorphic structures range from 0.002 to 0.079 µmol·(g·h)-1, with a mean value of 0.023 µmol·(g·h)-1. The ranking order of PNRs is pools > point bars > riffles > gravel bars > runs, with a seasonal change pattern of summer > spring > autumn > winter. ③ The areal nitrification rates (ANRs) across the five geomorphic structures range between 0.140 and 13.543 µmol·(m2·h)-1, with an average of 3.658 µmol·(m2·h)-1. In general, the highest mean value was observed in riffles, followed by runs, and gravel bars and point bars; the smallest value was observed in pools. In addition, ANRs appear to have seasonal change patterns similar to that of the PNRs. ④ According to the difference analysis, there are significant differences between pools or riffles and other features of the PNRs. Extremely significant ANR differences were observed between more than half of the geomorphic structures. ⑤ Regression analysis shows a stronger correlation between sediment nitrification and the overlying water environment, compared with the surface sediment properties.

[Nitrate Uptake Kinetics and Correlation Analysis in an Agricultural Drainage Ditch].

To investigate the whole-reach nitrate (NO3--N) uptake dynamics in a headwater agricultural stream, we performed five pulse tracer additions of a reactive solute (as KNO3) and a conservative solute (as NaBr) in an agricultural drainage ditch in Hefei district, Chaohu Lake basin, from October 2016 to April 2017. The TASCC (tracer additions for spiraling curve characterization) approach and Michaelis-Menten (M-M) method were applied for the simulation of NO3--N uptake dynamics. Results showed that the ambient areal rate of total NO3--N uptake Uamb varied from 11.40 to 69.13 µg ·(m2 ·s)-1 with an average of 34.45 µg ·(m2 ·s)-1, and the ambient uptake velocity Vf-amb averaged 0.24 mm ·s-1 and varied from 0.07 to 0.43 mm ·s-1 across three well-mixed sub-reaches in the study. The ambient uptake length Sw-amb averaged 199.06 m with a range from 92.51 to 405.74 m, which was much smaller than the length of the drainage ditch (about 2.5 km), suggesting that the agricultural drainage ditch had a high potential for NO3--N retention. Generally, the M-M model fit the NO3--N uptake dynamics well, and the maximum uptake Umax ranged from 158 to 1280 µg ·(m2 ·s)-1 with a mean of 631.13 µg ·(m2 ·s)-1. The half saturation constant Km ranged from 0.16 to 5.52 mg ·L-1 with a mean of 1.46 mg ·L-1. According to correlation analysis, Sw-amb was negatively correlated with NO3--Namb, and Uambwas significantly positively correlated with NO3--Namb, while other nutrient spiraling metrics were not correlated with the NO3--N ambient concentration. Hydrological conditions had no distinct effect on the NO3--N retention, but both the width variability Фw and variability in cross-sectional area ФA were significantly correlated with most of the nutrient spiraling metrics, indicating that geomorphic features in the drainage ditch evidently impacted NO3--N uptake.

T cells presenting viral antigens or autoantigens induce cytotoxic T cell anergy.

In the course of modeling the naturally occurring tumor immunity seen in patients with paraneoplastic cerebellar degeneration (PCD), we discovered an unexpectedly high threshold for breaking CD8+ cytotoxic T cell (CTL) tolerance to the PCD autoantigen, CDR2. While CDR2 expression was previously found to be strictly restricted to immune-privileged cells (cerebellum, testes, and tumors), unexpectedly we have found that T cells also express CDR2. This expression underlies inhibition of CTL activation; CTLs that respond to epithelial cells expressing CDR2 fail to respond to T cells expressing CDR2. This was a general phenomenon, as T cells presenting influenza (flu) antigen also fail to activate otherwise potent flu-specific CTLs either in vitro or in vivo. Moreover, transfer of flu peptide-pulsed T cells into flu-infected mice inhibits endogenous flu-specific CTLs. Our finding that T cells serve as a site of immune privilege, inhibiting effector CTL function, uncovers an autorepressive loop with general biologic and clinical relevance.

[Biotic and Abiotic Uptake of Phosphorus in Benthic Sediments of Suburban Streams Under Intense Human Disturbance Scenario].

To reveal the impact of land use change on the phosphorus uptake in benthic sediments of suburban streams, a headwater stream in the urban fringe of Hefei City was selected and a set of benthic sediments was collected monthly from the chosen stream reach from June to November 2016. An incubation method was applied to explore the biotic and abiotic uptake of phosphorus in benthic sediments under intense human disturbance scenario. Results showed that the uptake potentials in summer were higher than those in autumn, both for total (including biotic and abiotic) and abiotic uptake of phosphorus. Furthermore, both of these uptakes were distinctly higher for the third sampling site, which is adjacent to the sewage outlet, than those for the other sites. For all six sampling sites, the contribution rate of biotic uptake of phosphorus was significantly greater than that of abiotic uptake, both in summer and autumn. The monthly variations in potentials and contribution rates of phosphorus uptake indicated that intense human disturbance via land use change had a great impact on the biotic uptake of phosphorus in benthic sediments of the suburban stream.

[Nitrification and Denitrification Potential of Benthic Sediments in a Suburban Stream under Intense Human Disturbance Scenarios].

Water and benthic sediment samples were collected monthly from six sites over a 2-km reach in a first-order stream located in the northeastern rural-urban fringe of Hefei City, from May 2016 to January 2017. These sites were scattered in three stream reach types as natural pattern sections (Scenario 1), point source pollution sections (Scenario 2), and severe soil erosion sections (Scenario 3). The potential rates of nitrification and denitrification in the sediments were measured and variable characteristics were evaluated quarterly. Moreover, a difference analysis of each of the three scenarios and an influencing factor analysis for nitrification and denitrification potentials were subsequently conducted. Our results show that:① the mean value of the nitration ratios for total sediment samples is 0.381%, of which the maximum nitration ratio emerged in Scenario 2. As for Scenario 1, the nitration ratio in summer is the larger than in winter. The nitration ratios for Scenarios 2 and 3 rank from largest to smallest as spring > summer > autumn > winter. ② The mean value of the nitrification rate of the total sediment samples is 0.364 mg·(kg·d)-1, of which the maximum nitrification rate is associated with in Scenario 2. The nitrification rate is highest in winter, while similar for all other seasons in Scenarios 2 and 3. There is not much difference all year round for Scenario 1. ③ Average values for the denitrification ratio and denitrification rate for all sediment samples are 37.25% and 57.68 mg·(kg·d)-1, respectively. Both of these are higher for Scenario 2 than the other two scenarios for the same season. The ranking for denitrification for Scenarios 1 and 2 is summer > spring > autumn > winter, and spring > summer > autumn > winter in Scenario 3. ④ According to the difference analysis, significant differences not only exist between the nitrification rates between Scenarios 1 and 2 but also for the denitrification ratios and denitrification rates between Scenarios 1 and 3. In addition, there is an obvious difference in the nitration ratio between Scenarios 2 and 3. ⑤ Partial least-squares regressive analysis indicates that there is significant difference between the important influencing factors related to the nitration ratio and nitrification rate for each of the three scenarios.

[Pollution Characteristics and Nitrification and Denitrification Potential of Superficial Sediments from Streams in an Urban-Rural Fringe].

From May 2015 to June 2016, seasonal sediment samples were collected from three headwater streams in the urban-rural fringe of Hefei, Chaohu Lake basin, China. The nitrogen pollution characteristics of sediments were preliminarily investigated for the three streams. Three metrics, that is, potential nitrification rate (PNR), areal nitrification rate (ANR) and rate of denitrification were quantitatively determined, and their spatial and temporal variations were discussed subsequently. Moreover, the relationship between PNR, ANR or denitrification rate and a list of environmental factors was discriminated by using partial least-squares regression analysis. Results showed that:① Guanzhenhe Distributary was the most polluted stream with a mean content of 4516.39 mg·kg-1 for TN, which was 2.56 and 1.36 times higher than those of Modian Stream and Taochong Stream, respectively. Similarly, the highest values for NH4+-N and NO3--N emerged in Guanzhenhe Distributary while the lowest existed in Modian Stream. ② There were distinct seasonal variations in PNR and ANR, namely, the maximum values emerged in summer, minimum in winter, and almost equivalent in spring and autumn. And the arrangement in order for PNR and ANR was Taochong Stream > Modian Stream > Guanzhenhe Distributary. ③ The mean rate of denitrification in Guanzhenhe Distributary was 10.59 mg·(kg·h)-1, which was 3.16 and 1.75 times higher than those in Modian Stream and Taochong Stream, respectively. In addition, both denitrification rate and denitrification activity in summer were higher than those in spring for the three streams. ④ According to the variable importance plot (FVIP), ANR, PNR and rate of denitrification were almost all significantly correlated with such physical and chemical factors as pH, OM, NH4+-N, NO3--N, TN and TP in sediments for the three streams.

[Phosphorus Fractions and Release Risk in Surface Sediments of an Agricultural Headwater Stream System in Hefei Suburban, China].

A typical water system of agricultural headwater stream in Chaohu Lake basin was selected as the study area, and 17, 16, 14 and 13 surface sediments were collected from the four styles of stream, respectively, including ponds, branches, main channel and mainstream deep pools, in October 2014 (in autumn) and April 2015 (in spring). The forms and space-time variations of phosphorus in the sediments were analyzed. Clustering and variance analysis were conducted on the phosphorus forms data from the four styles of stream by means of multivariate statistical analyses. We quantified the phosphorus release risk (PSI) and identified the main impact factors of PSI via calculating the phosphorus sorption index (PSI) and the correlation analysis. The results showed that: (1) The contents of TP in the surface sediments ranged from 137.517 to 1709.229 mg x kg(-1) with an average value of 532. 245 mg x kg(-1), and the order of the average contents of phosphorus forms was IP (350.347 mg x kg(-1)) > OP (167.333 mg x kg(-1)) > Fe/Al-P ( 78. 869 mg x kg(-1)) > Ca-P (56.343 mg x kg(-1)) > Ex-P (6.609 mg x kg(-1)); (2) The contents of phosphorus forms had the same trend in all the four stream styles, which was deep pool > main channel > branch > pond; (3) In autumn, the deep pool and main channel were clustered into one class, while the pond and branch were clustered into the other class. In spring, branch, main channel and deep pool were clustered into the same class; (4) Variance analysis showed that the differences among the four stream styles were larger in autumn than in spring; (5) The PSI of the surface sediments ranged between 24.49 and 69.94 (mg x L(-1) x (100 g x micromol)(-1). The PSI in spring was lower than that in spring, indicating that phosphorus release risk of surface sediment was higher in spring than in autumn. (6) PSI had a significant negative correlation with Ex-P, IP and pH.

[Soil Phosphorus Forms and Leaching Risk in a Typically Agricultural Catchment of Hefei Suburban].

To investigate the soil phosphorus forms and leaching risk in a typically agricultural catchment of Ershibu River in Hefei Suburban, Chaohu Lake basin, 132 surface soil samples were collected from the catchment area. The spatial distribution of total phosphorus (TP) and bio-available phosphorus (Bio-P), and the spatial variability of soil available phosphorus (Olsen-P) and easy desorption phosphorus (CaCl2-P) were analyzed using the Kriging technology of AreGIS after speciation analysis of soil phosphorus. Moreover, the enrichment level of soil phosphorus was studied, and the phosphorus leaching risk was evaluated through determining the leaching threshold value of soil phosphorus. The results showed that the samples with high contents of TP and Bio-P mainly located in the upstream of the left tributary and on the right side of local area where two tributaries converged. The enrichment rates of soil phosphorus forms were arranged as follows: Ca-P (15.01) > OP (4.16) > TP (3. 42) > IP (2.94) > Ex-P (2.76) > Fe/Al-P (2.43) > Olsen-P (2.34). The critical value of Olsen-P leaching was 18.388 mg x kg(-1), and the leaching samples with values higher than the threshold value accounted for 16.6% of total samples. Generally, the high-risk areas mainly occurred in the upstream of the left tributary, the middle of the right tributary and the local area of the downstream of the area where two tributaries converged.