[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.

[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.

[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.

[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.

[Transient Storage Characteristics of Artificial Pool Geomorphic Structure in an Agricultural Headwater Stream].

From November 2015 to February 2016, five short-term tracer injections were performed with a conservative tracer (NaCl) in an agricultural headwater stream, Lake Chaohu basin. Thus the data sets of tracer experiments were finally employed for calculating the physical characteristics and transient storage metrics. Through the comparisons between the artificial pool reach and straight reach, characteristics of transient storage for the artificial pool geomorphic structure were interpreted and explored. Study results showed that: ① The ratio of As/A in artificial pool was larger than that in straight reach, whereas its value of exchange coefficient α was lower by an order of magnitude than that of straight reach. ② Artificial pool geomorphic structure had greater influence of transient storage on solute retention than that in straight reach, but its solute retention capacity of flowing water was weaker than that of straight reach. ③ It had a large ratio of As/A for the pool geomorphic structure, whereas its impact on the migration and transformation of solutes was less than that of straight reach. ④ Based on the Fmed200 metric, the transient storage accounted for 18.86% to 26.05% of travel time in artificial pool. For the straight reach, the Fmed200 metric had a range of 5.28% to 33.87%. In most cases, the values of Fmed200 metric in straight reach were higher than those in artificial pool. ⑤ Significant differences existed between artificial pool geomorphic structure and straight reach in the values of φw, φA and Ts, however, the differences were not significant in other indicators.

[Fractions and Release Risk of Phosphorus in Surface Sediments of Three Headwater Streams with Different Styles of Water Supply].

From May to September 2015, seasonal sediment samples were collected from three headwater streams and ditches which were discharged from sewage plant tail water, food processing wastewater and agricultural drainage-groundwater seepage, respectively, in Hefei, Chaohu Lake basin. The stream-bed sediments were analyzed for phosphorus fractions. The risk assessment on phosphorus release from sediments was conducted using the phosphorus sorption index (PSI), degree of phosphorus saturation (DPS) and the phosphorus release risk index (ERI). Moreover, nonparametric tests method was used to explore the difference among the three studied streams and ditches. Study results showed that:1 Guanzhenhe Distributary and Taochong Stream were seriously damaged by phosphorus pollution both in waters and stream-bed sediment, and the phosphorus pollution levels could be arranged in the order of Guanzhenhe Distributary >Taochong Stream >Modian Stream. The mean content of total phosphorus (TP) in sediments in Guanzhenhe Distributary was 1376.95 mg·kg-1, which was 2.94 and 1.91 times as high as those of Modian Stream and Taochong Stream, respectively. 2 Significant differences and different sort orders in contents of phosphorus fractions were found for each of the three streams. 3 Obvious seasonal variations existed in PSI for the three streams, and all the sampling points in the same stream had similar changing law, namely, the maximum content emerged in autumn, followed by winter, and the minimum occurred in spring or summer. 4 The same conclusions were drawn in phosphorus release risk according to the PSI, DPS and ERI, and the risk ranked as follows:Guanzhenhe Distributary >Taochong Stream >Modian Stream. 5 According to the difference analysis, significant differences existed in almost all of the indexes among the three streams.

[Influence of transient storage on solute transport and the parameter sensitivity analysis in a suburban drainage ditch].

From September to October 2013, five in-stream tracer experiments involving slug additions of chloride were performed in Guanzhenhe Branch, a headwater stream in suburban Hefei. From the perspective of different transport mechanisms such as transient storage, lateral inflow and advection-dispersion, four scenarios were set to analyze the effects of transient storage on solute transport in the drainage ditch. And sensitivity analysis of parameters in OTIS model was conducted. The results showed that transient storage exerted a significant influence on the peak values of simulated chloride concentration breakthrough curves (BTCs) in the main channel, and the REs (relative errors) of peak values in the BTCs ranged from 24.23% to 117.26%, which were much higher than those of the peak times. Meanwhile, the effects on simulated BTCs of transient storage markedly exceeded those of lateral inflow. Correlation analysis results showed that A(s)/A were significantly correlated with the peak value REs and the peak time RE's, respectively. Moreover, the ranking of parameter sensitivity in OTIS model was A > A(s) > α > D.

[Characteristics of nitrogen and phosphorus retention in two different channel forms in a typical headwater stream in the suburb of Hefei City, China ].

To investigate the characteristics of ammonium and phosphorus retention in two typical channel forms, deep pool and winding ditch in headwater stream, four field tracer experiments were conducted in a first-order stream of Ershibu River in Hefei suburban, in which a solution of biologically active (NH4Cl and KH2PO4) and conservative (NaCl) tracers was released to the head of each reach at a constant rate. According to the data sets of tracer experiments, mechanisms of ammonium and phosphorus retention were interpreted by using OTIS model code, transient storage metrics and nutrient spiraling theory. Study results showed that: (1) The value of As in deep pool was larger than that in winding ditch, whereas its value of hydrological parameter α was lower by an order of magnitude than that of winding ditch; (2) The value of NH(4)+ -λ in main channel was higher by two to three orders of magnitude than that of NH(4)+ -λs,in transient storage zone in deep pool, but in winding ditch the two parameters were closer in terms of numerical size; (3) In deep pool, the value of NH+(4) -Vf was higher by an order of magnitude than that of SRP-Vf, in winding ditch, however, not only the two values of NH(4)+ -Vf and SRP-Vf were close to each other, but NH(4)+ -Sw was nearly equal to SRP-Sw in numerical size as well; (4) The value of NH(4)+ -U was larger by two to three orders of magnitude than that of SRP-U in deep pool, whereas in winding ditch NH(4)+ -U was just larger by one to two orders of magnitude than SRP-U in size; (5) In general, significant difference existed between deep pool and winding ditch in the effect on ammonium and phosphorus retention, and marked retention efficiency was observed for ammonium rather than SRP in deep pool.

[Nitrogen and phosphate pollution characteristics and eutrophication evaluation for typical urban landscape waters in Hefei City].

To understand the water environment regimes of the city-circling water system in Hefei City, six typical landscape waters were chosen to investigate pollution characteristics of nitrogen and phosphate and evaluate water eutrophication level according to the monitoring data of water physicochemical characteristics and chlorophyll content from September 2012 to July 2013. Study results showed that (1) the six waters mentioned above have been seriously polluted by nitrogen and phosphorus loadings, with the monthly mean values of total nitrogen (TN) and total phosphorus (TP) concentrations far exceeding the universally accepted threshold values of water eutrophication; (2) the nitrogen contents in the waters of Nanfeihe River, Heichiba and Yuhuatang scenic spots exhibited a markedly monthly variation, and both TP and PO(3-)(4)-P in Nanfeihe River showed a fluctuated characteristic with high concentrations while presenting a significant upward trend in Yuhuatang scenic spot; (3) the average values of TN/TP ratios for Yuhuatang and Heichiba scenic spots were 104.7 and 158.3, respectively, and the ratios for Baohe Park, Yinhe Park, Xiaoyaojin Park, and city segment of Nanfeihe River were 16.8, 18.7, 6.4 and 16.8, respectively, indicating that the scenic waters of Yuhuatang and Heichiba were phosphate-limited whereas Xiaoyaojin Park was nitrogen-limited; (4) all the six scenic waters were, in general, subsumed under just two broad categories, namely Hechiba scenic spot and Nanfeihe River, which were seriously polluted, and clustered together, and the others fall into the second class; and (5) water eutrophication appraisal result indicated that the six waters were all in the state of eutrophication, and could be arranged in the order of eutrophication level, Yinhe Park > Heichiba scenic spot > city segment of Nanfeihe River > Xiaoyaojin Park > Yuhuatang scenic spot > Baohe Park.

[Distribution characteristics and erosion risk of nitrogen and phosphorus in soils of Zhuangmu town in Lake Wabuhu basin].

To understand the loss risk of soil erosion in the Zhuangmu town in Lake Wabuhu watershed, concentration and spatial distribution of nitrogen and phosphorus in 162 surface soil samples collected from the farmlands in ten administrative villages of the town were investigated. The risk assessment was conducted by using the nitrogen and phosphorus index method after speciation analysis of soil nitrogen and phosphorus. Based on ArcGIS technology, the spatial interpolation of total nitrogen (TN), total phosphorus (TP), and bioavailable nitrogen and phosphorus contents as well as nitrogen and phosphorus index values were performed by means of Kriging interpolation. The results show that, generally, average contents of TN and TP were obtained at 1.67 g x kg(-1) and 0.71 g x kg(-1), respectively. And the mean concentration of bioavailable nitrogen and phosphorus were estimated at 0.26 g x kg(-1) and 0.33 g x kg(-1), accounting for 14.93% and 47.30% of TN and TP contents, respectively. Spatially, the samples with high concentration of TN were mostly from Houji, Yangwan and Liuqian villages, whereas the samples sites with higher contents of TP located in Houji, Yangwan and Zaolin villages. The mean values of nitrogen index (NI) and phosphorus index (PI) for the whole town are 2.11 and 2.13, respectively. According to the numeric size of NI and PI, ten villages ranged in the order of Yangwan > Zhuangmu > Xueqiao > Liuqian > Lizhuang > Jinqiao > Zaolin > Zhangwei > Houji > Xugang village. In general, the soil nitrogen loss is dominated by low and medium risks in the Zhuangmu town, and high risk sporadically appears in local area of the Yangwan village. Like the nitrogen, soil phosphorus loss risk also gives priority to low, and above medium risk concentrates in the Yangwan village as well.